of Woody Ornamental Nursery
Plants in Florida
R. D. Dickey, E. W. McElwee, C. A. Conover, and J. N. Joiner
Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
F. A. Wood, Dean for Research
Container Growing of
Nursery Plants in Florida
R. D. Dickey, E. W. McElwee, C. A. Conover, and
J. N. Joiner
This public document was promulgated at an annual cost of
$9,265 or a cost of 92.6( per copy to provide information on
growing woody ornamentals in containers.
Mr. Dickey and Dr. McElwee are Professors Emeritus of Orna-
mental Horticulture with the Florida Agricultural Experiment
Stations and the Florida Cooperative Extension Service, respec-
tively. Dr. Conover is Director, Agricultural Research Center,
Apopka, and Dr. Joiner is a Professor, Ornamental Horticulture
Department, Institute of Food and Agricultural Sciences, Gaines-
First printing: December 1978
Second printing: June 1980
Cover photo.-A view of a Florida nursery producing container-
grown woody ornamentals.
I. IN TR O D U CTIO N ...................................... ................. 1
II. GENERAL INFORMATION ............................................... 2
Weight. Volume, and Area Measurements ..................... 2
Plant Materials ................................ ............. 2
III. PR O D U CT IO N .................................................. .............. 3
Information Center ..................................................... 3
Propagation ................................ ... ... . ................ 4
Sexual or Seed Propagation ................................... 4
Vegetative Propagation .............................................. 7
Cuttings ..................................... ................. 7
Propagation Structures .............................. 11
Bottom H eat .................... .. ................. 13
A ir Layering ..................................... .... ................ 14
D division ................. .. ........................................ 15
Grafting ........... ...................... .............. 16
G row ing M edia ...................................... .................. 18
M edia M ixtures .......... ........................ .. ................. 18
Characteristics of Media Mixtures ......................... 19
F unction .................. ..................... ............ 19
M edia A eration ................................ ... ...... ..... 19
Cation Exchange Capacity ..................... .......... 20
W ater Holding Capacity .................................. 21
Soil or Media Reaction-pH ............................... 21
Soluble Salts ................. ............ ................. 22
Carbon-Nitrogen Ratio .................. .................. 23
Shrinkage ......................................... ....... ........... 23
Freedom from Pests .................... ............. 25
M edia Com ponents ............................. .. ........ ......... 25
Sand ................................................... ................... 25
Perlite ........................................ 25
Calcined Clay ............................... ................... 26
Verm iculite .................................................... 26
Peat Moss ...................................... 26
Bark ................... .. ....... ...................... 27
Sawdust ................................... ............... 27
Shavings and Wood Chips ................................... 28
B agasse .............................................. ................ 28
R ice H ulls ................... ........................................ 28
M uck and Sandy M uck ........................................ 28
M edia M ixing M ethods ....................... ..... ............. 29
M ixers ----.......... .. ...................... ........2 29
Shredder-Mixers ........ .......... ...... 30
Front-End Loaders ................... ....... ...... 30
Suggested Media Mixtures .................... ........... 30
C ontainers ................................................... ........................ 31
Sales Appeal --.................................. ............ 32
G row th .......................................................................... 32
Container Durability ........................... -- ---.........- 33
Stacking and Shipping ............... .................. 33
Container Types ........................... -------.. ................. 33
Metal Containers ....................................... 33
Plastic Containers ............................................ 34
Clay Containers ..................................................... 34
P eat Containers .................... ............................... 34
Other Types of Containers .................................. 34
F ertilization ............................................ ........................... 35
Soil or Media Reaction-pH ........................................ 35
Fertilizers and Fertilization ......................................... 35
Nutrient Elements ................--............ ----...........-. 36
Macronutrients .............................................. 37
N itrogen -............ ........... .. ..... ............... 37
Phosphorus ...................................................... 39
Potassium ..................................... .............. 42
C alcium ........................................................... 44
M agnesium ................................. ........ ........ 45
Sulfur .......................... ................ .. 46
Micronutrients ................................ ...-- .............. 48
C opper .................................... .................... 48
Zinc .............................. ......... .......... 49
M anganese .......................... .......................... 50
Iron .......................... ................................... 52
B oron ........................ ................ ............... 54
M olybdenum ................... .......................... 55
Method of Application ......................................... 55
Fertilizer Materials .......................................... 56
Slow Release Fertilizers ---...............----....----........... 57
Fertilization Frequency -... --....-... -.......-............... 57
Fertilization R ates ..................................... ...... 58
Effect of Fertilization Rate on Growth
of Container Grown Plants ................ 59
Fertilizer Ratios ................. ---....... -................ 59
Fertilization Programs ....................................... 60
Soluble Salts .................................... .................. 69
Irrigation and Soil or Media Moisture .............................. 73
Crop Factors .. ............................ ...................... 74
Water Factors .................. ........... ----------.........-- 74
Soil or Media Factors .........--......----.... ............ -- 74
Water Requirements .......-.........-..- ----. .....-....-- ...... 76
Irrigation Systems ....-..--... -----------.........- .....----... -- 77
Overhead Irrigation .............-..............-....-........ 77
Individual Container Irrigation ........................ 78
Sub-irrigation ........................................................ 78
Other Irrigation System Uses ............................ 78
W eed Control ...... ...... ........ ........... ............ 79
Weed Control in the Container Nursery Area ........ 79
H erbicides ...................... ........ ..... ........ 79
Black Plastic .............. ....... ............ 81
M ulches ........ ..... ..... ... ........ .... .. 81
Weed Control in Containers ............................... .... 81
M edia Sterilization .............. ... .... .......... 82
M ulches ................. ........................... 82
Herbicides ..-.......................... .....- 82
Light and Temperature Relationships .... ......................... 84
Effects of Light .... ........... --..- .....-....... 84
Effects of Temperature ........--........ .......... 85
High Temperature Problems .........................-... .... 85
Low Temperature Injury .....- ......... .............. 86
Protection from Cold Injury .................... ..... 89
M echanization ............ .......... .... ... --.. .... ... -- 91
Irrigation System s ............... ..........--. ... 91
Media Pasteurization and Pasteurization-
Mixing Equipment ............................... .. 92
Media Mixing and Plant Potting Equipment ...... 92
Fertilizer Application Equipment ........... ..... 93
Pest Control Equipment ......................... ........ 94
Hauling W within Nursery .............. .................. 94
Pruning. Training, and Spacing Nursery Plants ..... 94
Pruning and Training .... ................. ... 94
Spacing ..... ..... .. .... ......... ................... .......... 97
Grades and Standards .................................... .. ..... .. 99
IV. INVENTORY CONTROL ............... ..................101
V. COST OF PRODUCTION ............................... ...... ..... .. 105
Types of Records ................................. ........... 105
Labor Efficiency ............. ... ............................ 107
Production Rate ............ .... ....... .. ...............109
Space Use Efficiency ................ ............................. 109
Level of Costs ................. .... .. ......................... 110
Price Level ................ .................. .................... 111
VI. BUSINESS ANALYSIS ................. ..................... 112
VII. REFERENCES ......... ........ ....... ...................... 116
The writers wish to thank Dr. E. W. Cake, formerly of the
Food and Resource Economics Department, for use of his data
on Business Analyses studies and for reading the sections which
deal with this subject.
Growing woody ornamental plants in containers has been
practiced for many years in Florida, going back to Glenn Saint
Mary Nurseries of Glenn Saint Mary, and Royal Palm Nurseries
of Oneco, which began operation in 1881 and 1882, respectively.
These firms were pioneers in the ornamental nursery business in
Florida. Most of their nursery stock was grown in the field, but
a limited amount was produced in containers, mostly clay pots.
This situation remained largely unchanged until World II when
metal No. 10 food cans became widely used in the food industry.
This provided nurserymen with a low cost container of adequate
size, and the cans soon came into widespread use. Today it is
estimated that 80% to 90% of the woody ornamental plants
produced in Florida are grown in containers, and this is increas-
The value of container grown woody ornamental nursery
plants in Florida has increased from this small beginning to a
yearly value in 1972 of approximately $38 million. This pro-
duction should continue sharply upward in the years ahead as
Florida's population continues to increase, along with increased
demand for plants in other sections of the United States.
Advantages of container growing over field growing include:
(a) extension of sales and planting seasons; (b) development of
more attractive sales packages; (c) easier transportability; (d)
greater control of environmental and cultural production factors;
and (e) more efficient use of production and sales areas.
The great increase in container growing of woody ornamental
plants has increased the need for information on production
practices that affect growth, quality, and cost of production and
thus the profitability of a nursery. Information from research
and experience dealing with production problems of Florida
nurserymen are brought together in this bulletin.
1 R. D. Dickey, former Ornamental Horticulturist Florida Agricultural Ex-
periment Stations, E. W. McElwee, former Ornamental Horticulturist,
Florida Cooperative Extension Service, C. A. Conover, Director, Agricul-
tural Research Center, Apopka, and J. N. Joiner, Professor, Ornamental
Horticulture Department, Institute of Food and Agricultural Sciences.
Abbreviations of several frequently used terms dealing with
measurements such as area, weight, and volume are used in this
bulletin for the sake of brevity. For this reason symbols for
names of certain often used chemicals and scientific and common
names of plants mentioned are given. The common names of
plants are used hereafter.
WEIGHT, VOLUME, AND AREA MEASUREMENTS
Abbreviations for weight, volume, and area measurements
used herein are:
1. Pound or pounds per acre-lb/A
2. Pound or pounds per acre per year-lb/A/yr
3. Pound or pounds per cubic yard-lb/cu yd
4. Pound or pounds per gallon-lb/gal
5. Volume in cubic inches-cu in
6. Parts per million-ppm
7. Area in square inches-sq in
8. Area in square feet-sq ft
9. Herbicides; Pounds of active ingredient per acre-
Scientific and common names of woody ornamental plants
mentioned are given below. Hereafter plants are referred to by
their common names.
Buxus microphylla japonica
Ilex opaca 'East Palatka'
Lantana sp. 'Cream Carpet'
Podocarpus macrophylla maki
'East Palatka' holly
Southern Indian azalea
An often overlooked area in planning and operation of a
nursery is development of an "Information Center." This area
should contain a library of standard reference books and other
publications on nursery management, plant materials, fertilizers,
equipment, landscaping, and other subjects related to ornamental
plants and nursery operations. A file should be developed of bul-
letins issued by the Florida Agricultural Experiment Stations1,
Florida Cooperative Extension Service', Florida Department of
Agriculture and Consumer Services,' and U. S. Department of
Agriculture3 that give information concerning nursery manage-
ment. Other sources of information are the Florida Plant Disease
Control Guide, Insect Control Guide, Nematode Control Guide,
and Weed Control Guide.4 These publications are kept up to date
with current information on pest control chemicals which have
EPA approval and rates to be used.
Another, but often neglected source for up-to-date research
information of benefit to Florida nurserymen is the "Proceedings
of the Florida State Horticultural Society." Different branches
of ornamental horticulture and related areas such as entomology,
nematology, botany, plant pathology, virology, soils, agricultural
engineering, and agricultural economics are covered in this pub-
lication. Membership in the Society is required to obtain a copy
of the Proceedings, but the cost is more than offset by value of
A catalog and operational files should be kept of the equipment
and materials used in the operation of a nursery. This will
facilitate daily operations, servicing, and parts replacement of
'Single copies of these bulletins may be obtained free fr6m the Office of
the County Extension Director.
4These bulletins are available from the Florida Department of Agricul-
ture and Consumer Services, Mayo Building, Tallahassee, Florida 32304.
:These bulletins may be ordered from the Distribution Section, Division
of Management Operations, Federal Extension Service, U. S. Department
of Agriculture, Washington, D.C. 20250. Some USDA bulletins are also
available from the Office of the County Extension Director.
4These guides may be ordered from the Institute of Food and Agricul-
tural Sciences, Building 664, University of Florida, Gainesville, Florida
32611. The Disease Control Guide, Insect Control Guide, and Nematode
Control Guide are $10.00 each; the Weed Control Guide sells for $15.00.
Florida residents add 4' sales tax.
equipment as well as increase ease of obtaining frequently used
materials such as pesticides, herbicides, fertilizers, containers,
and potting media ingredients.
Another important item in the efficient operation of a nursery
is to replace the "I guess so," "if I remember correctly", or "I
think that's right" method with an up-to-date loose-leaf book
containing information of often used, easily forgotten informa-
tion on materials, rates, procedures, application times, formulas,
etc., for a host of day-to-day nursery operations. These would
include use of materials such as insecticides, fungicides, nema-
tocides, herbicides, fertilizers, potting media, and soil fumigation
and pasteurization. The "knowledge book" should be readily avail-
able to all management personnel and indexed so that informa-
tion on any subject can be easily found.
Plant propagation is fundamental to agriculture and thus
to the existence of the nursery industry. Propagation is one of
the highest cost items in an ornamental nursery operation, and
success in this area is necessary for ultimate economic survival
of commercial enterprises.
There are two basic types of propagation: sexual (by seed)
and asexual (by cuttings, layering, grafting, or division). Seed
propagation usually requires fewer stock plants, and is initially
cheaper. However, more time is required to produce a salable
plant, and it generally results in seedling variations or production
of plants not true to type. Asexual types of propagation usually
guarantee plants true to the parent type, and result in salable
plants faster than from seed. Grafting allows for combination
of desirable characteristics from two or more plants.
SEXUAL OR SEED PROPAGATION
Seed propagation requires careful manipulation of germina-
tion conditions plus knowledge of individual germination re-
quirements of various seeds. Germination media should be well
aerated mixtures that will hold large quantities of moisture such
as combinations of peat and perlite, peat and sand, or similar
mixtures (1:1 by volume mixtures suggested). Seeds generally
should be germinated in flats, pots, or similar structures, and in
areas where they can be given the needed moisture, temperature,
and light controls during germination processes. The medium
should be well moistened prior to sowing seed.
An important problem in seed germination is depth of plant-
ing. Generally, seed should not be planted deeper than one or at
most two times diameter. For very fine seed this might mean
dusting them onto the medium surface and either not covering
or covering with a thin layer of shredded sphagnum moss. Larger
seed should be planted less than their diameter in depth, since a
2 to 3 inch depth is almost maximum for any seed.
Media on which seed are germinating should be sub-irrigated
where possible to prevent disturbing the seed and possibly break-
ing the young radicles (germinating roots) as they emerge.
Media and air surrounding germinating seed must remain moist
throughout the germination process. Seeds seldom survive if
they dry out after the germination process has begun. Covering
the germination facility (pot, flat, bench, etc.) with moisture-
proof plastic, glass, or some material to prevent moisture loss
from the media and immediately surrounding air during germi-
nation is desirable. Some fine seeds may, however, be germinated
under intermittent mist.
Materials used to maintain high moisture conditions around
germinating seed should not restrict the passage of air. Seed
germination requires high quantities of oxygen; thus plastic
coverings are recommended because they prevent loss of moisture
without affecting passage of air. Friable or open media for ger-
mination also favors air movement, and shallow planting of
seed helps assure ample oxygen for rapid germination.
The optimum temperature range for germination of seeds
of many woody ornamentals grown in Florida is 75-95F. Tem-
peratures should be maintained within this range for best re-
sults; however, research has shown that with many seeds a
variation of about 10-F between night and day stimulates ger-
mination compared with constant temperature. Thus, if bottom
heat or other temperature mechanisms are used for seed germi-
nation, provisions should be made to vary temperatures daily.
Seeds produced in fleshy fruit should be separated from the
fruit pulp immediately after harvest to prevent spoilage, fer-
mentation, and seed injury. There are several methods for doing
this, but for large lots some procedure for macerating or shred-
ding the pulp without damage to the seed should be used. Pulp
and seed can then be separated by flotation; this involves placing
them in water where heavy, sound seeds will sink to the bottom
and light pulp, empty seeds, and other extraneous materials will
float to the top.
Seed pods and capsules should be air-dried to increase ease
of seed removal. Seed extraction can then be done by use of a
rubber prong hammer-mill or rubbing through screens.
Many ornamental plant species grown in Florida produce
seed which have no dormancy and, therefore, will germinate
as soon as fruit are mature and harvested. Such seed should be
planted immediately after harvest. Longevity of seeds extracted
from pulpy fruit, particularly from tropical and semitropical
species, is often short lived (sometimes only 7 to 30 days), and
these seed are often very difficult to store successfully.
Recent research with citrus seed indicates a possible method
for storing these and other similar seeds. Seeds are removed
from the fruit, surface dried in a cool area, treated with a fungi-
cide such as 8-hydroxyquinoline sulfate at 1:100 concentration,
placed in moisture proof plastic bags, and stored at 360F. Citrus
seed have been successfully stored for 3 to 4 years by this
Some plant seeds propagated by nurserymen in Florida have
a dormancy factor which must be considered in germination.
Perhaps the most common cause of dormancy is the imper-
meability of seed coats to water, gas exchange, or both. The
usual method of overcoming this is manual scarification. This can
be done by revolving in a drum lined with sandpaper or other
abrasives, or seeds can be mixed with sharp sand and revolved
in a container. Small lots of seed can be abrased by rolling them
on a cement floor using a brick or board. Examples of seeds
having hard and impermeable seed coats include Jerusalem-
thorn (Palrkinsonia aculeata) and redbud (Cercis canadensis).
Seeds of other species such as American holly (Ilex opaca),
southern magnolia (Magnolia grandiflora), nandina (Nandina
domestica, and sweet gum (Liquidambar styraciflua) have em-
bryos or endosperms that are non-functional or contain inhibi-
tors at time of seed maturity. They require an after-ripening
period before they will germinate. After-ripening is accom-
plished by stratifying or layering seed between moistened ma-
terials such as cotton, peat, or sand in a well-ventilated container
and placing in refrigeration at 40 to 450F for various periods
of time. Most seed will complete after-ripening in 3 months of
storage under proper conditions, but some such as southern
magnolia require as much as 6 months. After-ripened seed must
be planted immediately after removal from refrigeration, or
they will return to a dormant state and require an even longer
after-ripening period the second time, plus loss of viability.
There are other factors which prevent some seed from ger-
minating immediately upon maturing. Many of the mechanisms
involved are still unknown. An example is the Canary Island date
palm (Phoenix canariensis). Seeds from this tree germinate er-
ratically and over long periods of time unless the thin cutin
waxy film over the hilum (scar or mark indicating point where
seed was attached) is removed. When this film is removed, the
seed will germinate immediately. Considerable research is needed
on germination of seeds of other species grown in Florida, es-
pecially on other species of palms.
Media used for germinating seed should be sterile to prevent
loss of seedlings from disease. A common disease problem with
seedlings is damping-off caused by species of Pythibun and Rhi-
zoctonia. Media can be heated or fumigated with chemicals to
eliminate weed seed, nematodes, and disease organisms.
The most common and satisfactory types of cuttings for most
woody ornamentals grown in Florida are stem cuttings. They
can generally be divided into terminal or tip cuttings and sub-
terminal or cane. Tip cuttings often produce the most desirable
plants for many species, and they often root faster than sub-
terminal cuttings due to age of material. Tip cuttings are made
by removing the terminal 4 to 6 inches of branches. Subterminal
or cane cuttings are made by cutting 4 to 6 inch sections of stem
or cane (as in the case of roses) below the terminal section.
Leaf bud cuttings, sometimes known as leaf stem or mallet,
are particularly valuable when propagating material is scarce
or where other types of stem cuttings will not root, as with cer-
tain hybrid Chinese hibiscus. These are made by taking a leaf,
petiole, and stem piece cut approximately 1// inch above and
below the point where the leaf is attached. These cuttings con-
tain an axillary bud to provide new top growth.
Age of wood can be important in percentage of rooting, length
of time to rooting, and quality of root system formed. Wood of
some plant species more than one year old will not root, whereas
in others, age is relatively unimportant. Current season wood
that is approximately 6 to 10 weeks old generally provides the
best material for cuttings under most conditions.
Maximum amount of leaf surface should be left on cuttings
for best rooting response. Removing all but terminal leaves, or
cutting leaves in half to reduce water loss from the cuttings, has
been proven detrimental to the rooting process. Other methods
of reducing transpiration or water loss from cuttings should be
practiced rather than leaf surface removal. Leaves produce food
and natural hormones necessary to stimulate optimum root
initiation and development, and any reduction of leaf surface
reduces root quality and delays rooting.
Cuttings should be taken from non-wilted plants and treated
so as to prevent moisture loss until rooting has occurred. As
cuttings are taken, they can be placed in large moisture proof
plastic bags or moistened burlap bags to prevent moisture loss
until they are stuck. Ideally cuttings should be maintained in a
humid, warm, but not hot atmosphere for at least 1 to 2 hours
from time of taking until time of sticking to allow a protective
suberin layer to form.
Use of rooting hormones has been investigated at the Uni-
versity of Florida, and at other institutions. Results have been
extremely variable. Auxins used as rooting hormones may stim-
ulate rooting in very low amounts and inhibit rooting in higher
concentrations, so they should not be used indiscriminately. The
range between beneficial and toxic levels is often extremely
narrow. Such materials applied by a propagator may enhance
or counteract naturally produced hormones in plants. Because
the natural levels of hormones in plants vary seasonally due to
temperature changes, fertilizer levels, watering practices, stage
of growth of plants, and other factors, the same amount of
auxins that may stimulate rooting at one time may prevent root-
ing at another time.
Some plants will root easily without applications of auxins,
and usually with such plants addition of auxins often retards
rooting. Hormones should not be used, therefore, without care-
ful testing by propagators using different concentrations at dif-
ferent seasons of the year with varying plant materials. Over a
period of years sufficient information can be obtained to make
use of the auxins that benefit rooting of certain plants.
Commercially the most convenient method of applying auxins
is by dipping basal ends of cuttings into powdered talc contain-
ing the hormone. Several commercial preparations are available
containing various concentrations of different materials. The
auxins most commonly used and which have proved most suc-
cessful are IAA (indoleacetic acid), IBA (indolebutyric acid),
and NAA (naphthaleneacetic acid). Of the three, IBA and NAA
are more effective with more plant materials than IAA. Gen-
erally, woody material, which is more difficult to root, should be
treated with powders having high concentrations. Some com-
mercial preparations contain combinations of two auxins, and
research indicates these combinations, particularly IAA with one
of the other materials, are more effective on hard-to-root materi-
als than either alone. Cuttings should be inserted into the root-
ing medium immediately after treatment. A thick bladed knife
might be used to make a trench in the rooting medium before
inserting cuttings when talc has been used as the auxin carrier
to prevent brushing off the powder while sticking.
Dilute solutions of auxins may also be used satisfactorily, al-
though this is a more difficult and cumbersome method for most
commercial nurserymen. Concentrations for dilute solutions
vary from about 20 ppm for less-difficult-to-root species to ap-
proximately 200 ppm for more-difficult-to-root plants. Cuttings
are usually soaked in dilute solutions from 12 to 24 hours prior
to sticking. An approximately 100 ppm solution of auxins, for
example, can be prepared by dissolving a level 1/4 teaspoon of the
chemical in a small amount of ethyl alcohol and adding to 1
gallon of water. This should be stirred thoroughly.
Many propagators prefer the concentrated solution dip
method. Concentrations for these solutions range from 500 to
10,000 ppm, and dip time ranges from 5 to 10 seconds. After
dipping the cuttings are inserted immediately into rooting media.
The concentrated dip method is convenient and fast, and gener-
ally gives more uniform results than the other two methods.
A typical solution of approximately 4,000 ppm solution of
auxins can be prepared by dissolving a level 1/ teaspoon of the
pure crystals in 31/3 fluid ounces of 50% ethyl alcohol.
Subterminal and cane cuttings usually respond to auxin
treatments more than tip cuttings because of the older wood
involved. Older plant tissues normally have less natural auxins
than younger tissue.
Auxin treatments are not a substitute for good propagation
techniques. They produce positive responses only when some
other environmental factor or combination of factors such as
temperature or old wood are less than optimum.
Light intensity is an important factor affecting speed and
success of rooting. Where mist is used for maintaining high
water relationships in cuttings during rooting, full sunlight is
best for rooting of most species of woody plants. Generally, the
highest amount of light the plant will tolerate during propaga-
tion is recommended. Light is a basic fuel for synthesizing car-
bohydrates and auxins by plants, and within limits, the higher
the light intensity, the greater the amounts of these items pro-
duced to support and stimulate root initiation and development.
However, in a few cases etiolation of propagation material is
used to improve rooting of some cuttings.
Depth of sticking cuttings is also an important consideration
often overlooked by propagators. Root initiation and growth re-
quire large amounts of oxygen from the air. Therefore, the root-
ing area should be as close to the top of the medium as practical
in order to obtain adequate aeration. The cutting should be stuck
only deep enough to hold it upright, usually 1 to 2 inches, de-
pending on the medium and size of the cutting.
High water holding capacity and excellent aeration proper-
ities are the prime considerations in selecting media. Usually one
material does not provide both; therefore, a mixture is required.
Peat is the organic material most used to provide outstanding
water holding capacity, but when used alone does not provide
good aeration. Aeration is provided by utilizing a coarse in-
organic material such as sand or perlite. Shredded pine bark,
when available, is an excellent substitute for peat. Research at
the University of Florida has indicated that a mixture of or-
ganic and inorganic materials such as peat and builders sand
or peat and perlite, in a 1:1 by volume mixture, is an excellent
medium for rooting a wide range of woody plants under many
different cultural conditions. Drainage and aeration are particu-
larly important for mist systems because of the high amounts
of water used during rooting.
Cuttings should be taken from plants that have obviously
received adequate fertilization. Those from plants showing nu-
tritional deficiencies will give a lower percentage of successful
rooting, take longer to root, and produce poorer quality root
systems. Rooted cuttings from such plants take longer to begin
growth when transplanted than would otherwise be true.
Mist systems provide the best way of maintaining high water
relationships within cuttings during rooting. Misting has done
more to increase rooting success in many species than almost
any other propagation technique, but such systems have ad-
vantages and disadvantages. Utilization of a mist system allows
success with cuttings that require long periods for rooting, and
it makes possible rooting under conditions of maximum light
intensities. Misting usually produces higher rooting percentages
in less time and results in higher root quality than any other
system currently in use. Cuttings rooted under mist generally
have fewer problems from insects and diseases during rooting.
The major problem with mist propagation results from
leaching of nutrient elements from leaves due to excess water-
ing. This loss of nutrients increases mortality of some species
after removal from the mist and delays growth following trans-
planting. Mist can lower temperatures of media below optimum
and thus slow rooting.
To be most satisfactory mist nozzles must break droplets
into very fine particles or fog so that droplets fill the area around
cuttings, wetting both sides of leaves. The primary function of
mist is to produce a continuous film of water over the entire
surface of cuttings. The finer the droplets size, the better the
coverage. Time clocks should be installed to turn the system on
about daybreak and off after sunset since misting at night is
usually not necessary. There are a few exceptions, such as dif-
fenbachia, that respond to night misting. Addition of interval
timers to provide minimum cycles of mist during daylight hours
will also allow reduction of water use and thus reduce excessive
leaching of nutrients. Cycles, such as 3 seconds of mist in each
10 minutes or 2 seconds per minute, will have to be adjusted to
cultural and environmental conditions existing at individual
nurseries. Systems should also be adjusted for seasonal and
other environmental variations. An absolute requirement is that
a film of water be constantly present over the entire cutting
surface and adjustments must be made to attain this. Once cut-
tings are begun under mist, they must remain misted until well
rooted. Failure of the mist system for any reason will rapidly
result in heavy losses.
Rooted cuttings transplanted from mist systems should be
placed under reduced light intensity by shading and watered
3 to 4 times per day for a week to 10 days to become acclimated
to a lower humidity environment. Gradual reduction of shade
and watering will aid in reducing losses.
The purpose of propagation structures is to expose large
numbers of cuttings to ideal rooting conditions (maximum light,
high humidity, and adequate aeration) previously discussed.
Intermittent mist is excellent for producing these conditions,
and is now used by Florida nurserymen for propagation of prac-
tically all their cuttings.
Some types of structures used in propagation are: (a) con-
ventional glass greenhouses (Fig. 1); (b) fiberglass green-
houses; and (c) metal or wooden frames covered with a plastic
film. These structures are listed in the order of decreasing costs.
Some advantages of closed structures are better control of root-
ing media temperatures, especially during colder months of the
year, and elimination of the wind factor which may cause uneven
distribution of the mist. Size of propagation structure and
amount of bench space needed will be determined by number of
cuttings the nurseryman wishes to propagate. If the nursery is
just beginning operation, the type of structure used may be de-
termined, in part, by available funds. When funds are limited
but the nurseryman needs large numbers of cuttings during the
year, this can be accomplished by budgeting propagation through-
out the year to the season or seasons the species root best.
In Florida two methods are largely used to place cuttings in
propagation benches under mist. They are (a) the long used
conventional "stick and pull" method, in which the entire bench
is filled with rooting medium, and (b) use of small individual
containers such as small plastic or peat pots for rooting each
cutting. The individual container method is on the increase, and
has partially replaced the older bench method. A popular size pot
used for this purpose is a square or round pot 21/2" across and
31/4" deep. When peat pots are used, the rooted cuttings are
planted pot and all.
Bench size is determined by: (a) size of enclosing structure;
(b) location within structure (along sides or in center, etc.);
and (c) number of cuttings to be propagated. Benches should be
raised for good drainage and to improve sanitation. A con-
venient bench height is to have the bottom approximately 30
inches from the ground. Maximum convenient width for propa-
gation benches is approximately 60 inches with sides about 6
inches high. Propagation medium in the bench should not be
Figure 1.-Propagation structure used in a Florida ornamental nursery.
Cuttings are "stuck" in small plastic pots and the pots placed in flats. The
bottom of the propagation bench is covered with hardware cloth which
allows heat from steam pipes underneath the bench to warm the rooting
deeper than 4 to 5 inches. Propagation benches may be con-
structed of wood, which if treated with a wood preservative will
last several years, or with a long lasting material such as tran-
site. Wooden bottom boards should be placed lengthwise of the
bench and far enough apart (at least 1/ inch after they have
swollen from the water) to insure good drainage. Hardware
cloth should also be placed in bottom of the bench. In using tran-
site the corrugated sections should be placed across the bench
to prevent the medium from falling through. A type of propa-
gation bench that is gaining popularity in Florida is constructed
with sides made either from transit or wood and bottom made
from hardware cloth. This type of bench provides excellent
drainage and aeration, and it allows for use of bottom heat
provided by steam pipes running underneath benches. When this
method of supplying bottom heat is used, plastic flaps should be
attached to sides of benches and allowed to reach the ground
for more efficient heating.
There are several ways in which water line and mist nozzles
may be arranged, but a commonly used method is to run line on
bottom and down center of the propagation bench with standards
(18 to 24 inches tall), each tipped by a mist nozzle, arising from
it at intervals. Distance between the standards varies depending
on water pressure, type of nozzle (whether deflection, oil-burner
type, etc.), and width of bench, but is usually 4 to 5 feet. Rela-
tively inexpensive deflection type nozzles are satisfactory. For
automatic operation the intermittent mist system requires a day-
night timer connected to a short-interval timer (one commonly
used type can be set to turn on for intervals of from 1 to 6 or
more seconds of each minute) which is then connected to a
solenoid valve to turn mist off and on during the daylight hours.
A strainer should be placed in the water line between the water
source and solenoid valve.
Arrangment of water lines and mist nozzles as described
above is similar for outdoor propagation benches, but such
benches should have a plastic baffle extending around the bench
and vertically from upper edge of bench for at least 21/ to 3
feet above the bench. There are also several types of plastic
tents which can be constructed to cover outdoor propagation
The use of this rooting aid has proven successful in: (a) de-
creasing rooting time; (b) increasing percentage of cuttings
that root; (c) protecting cuttings of tender species from freezing
during cold periods; (d) aiding propagation of hard to root
species; and (e) aiding propagation during colder months of
the year. Generally, two methods have been used to supply bot-
tom heat in Florida: steam pipes and electric coils. When steam
pipes are used, whether rooting medium is placed in the bench
or in individual rooting pots, the bottom of the bench should
be made of hardware cloth so that heat coming from steam pipes
running underneath the benches may warm the medium. The
second method is to use electric heating coils placed along bottom
of the bench. Low voltage heating units are available which in-
clude the recently developed low voltage heating wires. Remem-
ber that if rooting medium in the bench is too deep (over 5
inches) this will reduce the beneficial effects to be obtained
from bottom heat, and also reduces aeration.
Layering, generally, is a method of inducing rooting of a
stem while it is still attached to the parent plant. There are
several types of layering, including tip, simple, compound, and
air layering or marcottage (Fig. 2). Air layering is the only
type of layering used to any extent by nurserymen in Florida.
It is used to propagate a few special plants such as certain
species of rubber plants (Ficus spp.).
The first step in layering is removal of a strip of bark 1/2 to
1 inch wide to 6 to 12 inches from the tip of any desired branch.
The exposed surface from the girdled area should be scraped to
retard healing which, in turn, would reduce rooting. Another
way of accomplishing the same effect as girdling is to make
a slanting cut approximately 2 inches long up and into the center
of the stem, keeping the two cut surfaces separated by inserting
a small stick such as a toothpick or a small amount of spagnum
moss. Application of IBA or other rooting compounds to the
wound surface has been reported to speed up rooting in a few
species being air layered. The next step is to cover the stem
around the wound with approximately two handfuls of moistened
sphagnum moss. This is either wrapped with a waterproof plastic
film, with the ends twisted and taped to prevent loss of water
from the moss, or wrapped with aluminum foil shaped like a
cup to catch moisture from rain or irrigation. The biggest prob-
lem with air layering, in addition to its high labor requirement,
is drying out of the sphagnum moss covering the wound area.
The waterproof plastic film will prevent moisture loss if properly
wrapped around the layered area, but with materials that re-
Figure 2.-Steps in making an air layer on a branch using a moisture-
proof plastic wrapper. Top, branch girdled-first step in the operation.
Middle, wrapper in place and moist sphagnum moss placed over girdled
area. Bottom, ends of wrap have been twisted tight and tied with rubber
bands, completing the operation.
q\zire a long time for rooting the sphagnum might dry out, and
birds will peck holes in the film.
Use of aluminum foil is faster and more convenient to use,
but allows the sphagnum moss to dry out more rapidly than the
plastic film, and Trequires more care to see that the sphagnum
moss is kept moist tstoist is taken care of by
rain or irrigation. The foil and film could be used together.
This easy and rapid method of propagation consists of simply
dividing the plant into sections possessing active tops and roots.
Some woody ornamentals that may be propagated by division
are nandina (Nnd ri v do mestica), cape plumbago (Plumbago
are nandina (Nandina domcstica) cape plumbago (Plumbago
capensis), sea-grape (Coccolobis uvifera), the jasmines (Jasmi-
num spp.), oakleaf hydrangea (Hydrangea quercifolia), and
many species of palms.
Grafting is the art of joining parts of plants together in such
a way they will combine and continue to grow as one plant.
Many consider grafting as the joining of parts of two or more
different plants together, but sometimes in the nursery industry
a seedling is severed and immediately joined back together to
reduce time of the juvenile stage in some species. This is also
grafting. Grafting is a difficult propagation technique, and it
requires considerable skill by the grafter for economical success.
There are many reasons which make this difficult task worth-
Some primary reasons for grafting are: (a) to change size
of the resultant plant by dwarfing or increasing growth; (b) to
adapt the plant to a wider range of soil and environmental con-
ditions; (c) to introduce a rootstock that is disease or nematode
resistant; (d) to change the form of plants, as in the production
of tree roses and ivy; (e) to produce earlier flowering and fruit-
ing; and (f) to provide a vegetative propagation for plants that
cannot be produced from cuttings or other vegetative means.
The most common types of grafts used in the ornamental in-
dustry are illustrated in Fig. 3. Whip or tongue grafting is par-
ticularly useful for grafting relatively small material, 1/4 to 1/2
inch in diameter, and where both scion (top part of the graft
partner) and stock (basal part of the graft) are of approximate-
ly the same size. This technique gives considerable structural
strength to the union during healing. Saddle grafting is used
under similar conditions as the whip graft, but since this does
not provide good structural strength for union, it is recom-
mended only with materials that heal rapidly and will be kept
under controlled conditions during the healing process. It is an
easier method than whip grafting and can be accomplished
faster by a larger number of people. A new technique has been
developed in which a pin is pushed into both rootstock and scion
of a saddle graft while placing the two parts together to give
additional strength to the union until the wound has healed. The
pin apparently does no damage to the plant during its life.
Bark and cleft grafts are usually field techniques used to
change plants of undesirable types into desirable varieties. Cleft
C 2 3
Figure 3.-Three types of grafts used in Florida's ornamental nurseries.
A. Steps in making a whip or tongue graft: (1) long oblique cut made
in stock; (2) make a sloping cut into the stock; (3) similar cuts are made
on the scion; and (4) stock and scion are fitted together.
B. Steps in making a saddle graft: (1) stock showing where cut is
made; (2) stock cut off; (3) method of cutting stock and scion; and (4)
stock and scion are joined to make the saddle graft.
C. Steps in making a cleft graft: (1) scion showing long wedge-shaped
cut and cross-section; (2) scion fitted in stock, (a) cambium matched;
(3) scion and stock secured by tying with a rubber band; and (4) point of
union can be protected by using either a plastic wrap, grafting wax or
grafts can be used on small and large materials, and is often
used in grafting camellias.
In grafting, one should align the stock and scion with as
much cambium connected as possible, then cover or wrap the
union with some material that will maintain a high moisture
relationship around the graft union and still allow ample move-
ment of air. The ideal wrapping material is a waterproof plastic
film which prevents water loss from the wound but allows pas-
sage of air. Temperatures ranging from 75 to 950F should be
maintained until the union is completed to speed up healing and
to allow for adequate joining of the two parts.
Many propagators are now rooting and grafting in one oper-
ation, especially with materials such as roses and gardenias. In
such cases unrooted cuttings of rootstock and scion material are
made, and the scion is grafted onto rootstock pieces that have
had their terminal removed. The grafted cutting is then stuck
in the rooting medium under mist. By the time rooting has
occurred, the graft is healed and the combined plant is ready
for transplanting. This procedure saves considerable time and
works well for several plant materials.
Media mixtures that produce quality container grown woody
ornamental plants generally have similar physical and chemical
properties. Without these, economical production of container
grown plants outdoors in Florida is not possible. In fact, the
wrong media mixture can increase problems and costs to the
extent that it becomes difficult to produce economically under an
otherwise satisfactory cultural system. Media mixtures function
in a number of ways, but certain factors must be present to re-
duce problems encountered by nurserymen and thus to maximize
profits. The objective of any good growing medium is to produce
a quality plant in the shortest time period with lowest total pro-
When calculating media costs, include all production factors
such as initial costs of components, mixing equipment, rate of
plant growth, and number of quality plants produced within a
specified time period.
An ideal media mixture for plant growth is usually described
as one with 25% water, 25% air, 45% mineral soil (which in
Florida would be sandy soil) and 5% organic matter. This would
not be exactly correct in Florida where such a high percentage
of sand in the mixture would allow rapid drying due to low
water holding capacity and excessive leaching of nutrient ele-
ments. Preferably, mixes using sand should contain 50c' sand
and 50' organic matter by volume, which means approximately
4/5 sand and 1/5 organic matter by weight. Other important
factors to consider in media mixtures include medium weight,
cation exchange capacity, carbon:nitrogen ratio, pH, soluble salt
level, and rate of organic matter decomposition.
Usually combinations of two or more materials are necessary
to obtain the ideal characteristics of growing media for plants.
The mineral component (sand or similar material) usually pro-
vides weight and substance to hold the plant upright and pro-
vides adequate pore spaces for good aeration, but has low water
and nutrient holding capacities. Organic material, on the other
hand, usually has excellent water and nutrient holding capabili-
ties, but when moist has very little porosity for proper aeration
of plant roots. Proper mixtures of the two types of components
will give all the desired growing characteristics.
Ingredients used in making media should be readily available
to growers, relatively inexpensive, uniform so that mixtures can
be standardized and reproduced, sterile, low in soluble salts, and
free of any substance which might be toxic to plants.
CHARACTERISTICS OF MEDIA MIXTURES
The primary functions of media are to provide ideal environ-
ments for root growth and an adequate base for anchoring
plants. Its native or natural fertility level is unimportant, inas-
much as a nutritional program can be devised to provide all
essential elements for plant growth. Completely inert materials
can be used as media components if they provide proper environ-
ments for root growth.
Roots cannot absorb water and/or nutrients except in the
presence of oxygen. In the growth and absorption processes roots
give off relatively large quantities of carbon dioxide which can
become toxic unless removed. Media for root growth must allow
for rapid exchange of air so that the carbon dioxide is removed
and oxygen is supplied constantly to root surfaces. This means
that even in the presence of adequate moisture sufficient air
spaces must exist throughout the media for rapid and free air
exchange. Factors within the media which affect porosity in-
clude size, uniformity, and types of particle components.
Organic materials used should be fibrous and somewhat
coarse. Particle size of highly decomposed material such as muck
is extremely fine; such material becomes slimy when wet and
results in poor drainage and aeration. Peat or pine bark that has
been through a hammer mill makes a more optimum organic
component. Sand or other mineral materials used in mixes
should be medium grained and should not contain a range of
particle sizes from fine to coarse, because fine particles fill in
spaces between medium sized particles and these, in turn, fill
in spaces between coarse particles. The combination sets up and
becomes quite hard. A good mixture should drain freely and
rapidly, yet maintain a high moisture content. Free and rapid
drainage indicates adequate aeration.
CATION EXCHANGE CAPACITY
This term refers to the ability of a soil or media mixture to
retain nutrients against leaching by irrigation water or rainfall.
As cation exchange capacities of Florida mineral soils are very
low, organic or inorganic materials must be added to media
mixtures to hold nutrients against leaching, provide a buffer
capacity to prevent rapid changes in nutrient availability, and
act as a nutrient reservoir. However, addition of more than
50% to 60% by volume of organic matter can cause problems
from lack of leaching with the resultant build-up of soluble
salts, unless watering is increased at least periodically to leach
excess salts from the container. Although a high nutrient-holding
capacity is desirable, some thought must be given to soluble salts
build-up which may cause injury to plants. The nutrient-holding
capacities of soils or media are measured by the number of units
of nutrients held by a given quantity of soil or media (milli-
equivalents per 100 grams of soil). Heavy sandy-clay soils may
therefore have more nutrient-holding capacity than a light-weight
100% organic soil. The weight per unit of volume or bulk density
of the soil or media mixture determines this factor. A nutrient-
holding capacity (cation exchange capacity) of 5 to 10 milli-
equivalents per 100 grams of medium in a sand-peat mixture is
satisfactory for good plant growth, while a level of 30 units may
be necessary in a mixture made up primarily of light-weight
peat or other organic matter to have equal total nutrient-holding
capacities (cation exchange capacities) of many readily avail-
able soil components.
WATER HOLDING CAPACITY
This is a measure of the amount of water held by a medium
after free drainage has occurred, and is expressed usually in
percent of dry weight, but should be reported in percent by
volume. The amount of water held against the pull of gravity
will depend upon the surface area of media particles per unit
volume, and the attractive forces acting between the water and
the particles. Organic materials such as peat and bark will add
water holding capacity to sands up to approximately 50% to
60% by volume of the mixture. Rates higher than 50% to 60%
of organic materials in a growing medium will usually reduce
percentages of water held by volume.
The media should be sufficiently friable (loose) so that water
is held predominantly in a film adjacent to individual particles,
leaving air spaces for proper aeration. Compaction of medium
prevents free drainage, causes saturation of the media mass, and
results in insufficient aeration for proper root growth. Ideal
mixes for container growing will hold 35% to 50% moisture by
volume immediately after free drainage has occurred following
SOIL OR MEDIA REACTION-pH
The pH is a measure of the acidity or alkalinity of the soil
or media solution which bathes the root system. A pH of 7 is
neutral. As a solution drops below this level in pH it becomes
more acid, and as it increases in pH above this level it becomes
more alkaline. Each unit of increase or decrease in pH changes
the acidity or alkalinity by a factor of ten. For example a pH of
5 is 10 times more acid than a pH of 6.
The pH is important in the growth of plants because it affects
solubility and, thus, availability of nutrient elements necessary
for plant growth which are absorbed from the medium through
the root systems. The ideal range of pH for optimum plant
growth is 5.8 to 6.2 because within this range elements in the
media are most available for absorption by roots. As the pH
becomes increasingly higher or lower than this range, many of
the nutrient elements become either chemically bound so they
are insoluble and unavailable to plants, or they become soluble
and leach from the medium. More detailed discussion on avail-
ability of individual elements at various pH ranges will be found
in the section on fertilization.
Acid or low pH can be increased by adding some type of
limestone such as calcium carbonate, calcium hydroxide (hy-
drated lime), or dolomite, which is a combination of calcium
carbonate and magnesium carbonate. In addition to pH correc-
tion these materials provide much of the calcium and, where
dolomite is used, magnesium necessary for plant growth. Alka-
line pH can be reduced by the judicious use of sulfur. Most or-
ganic materials and many Florida sands are natively acid, as
are most fertilizer materials. Therefore, liming for correcting
low pH is a more common problem than adding acidifying agents
to correct alkaline situations. Table 1 gives amounts of materials
to add in adjusting mixtures to the desired pH.
Table 1. Approximate amount of materials required to change the
reaction of some soils.'
Pounds per 100 square feet to change
pH of acidity to pH 5.2 for2
Sandy soil Loam soil Muck or peat
Add sulfur or acidifying mixture to lower pH to 5.2
7.0 2 3 6
6.5 1 2 5
6.0 1 2 4
Add dolomitic lime to raise pH to 5.2
4.5 2 3 7
4.0 4 7 15
3.5 7 10 23
1 Table 1 from Agr. Ext. Ser. Bul. 161A, Growing camellias in Florida.
2For a wheelbarrow of soil (21/2 bu) add 1/15 of above amounts.
For a sq. yd. of area (9 sq ft) add 1/10 of above amounts.
For a cu. yd. of soil (27 cu ft) add '/ of above amounts.
Careful consideration should be given to salts present in
media mixtures. Many growers have experienced problems with
high soluble salt levels in their growing medium as a result of
utilizing alkaline or saline components. Establishing criteria for
acceptable maximum levels of soluble salts in media components
is difficult, and depends to a large extent on soil moisture and
fertility levels maintained by each grower. However, the ap-
proximate limits in MHOS x 10-5 for a 1:2 mix of dry soil or
media to water mixture by volume are: sandy soils 75, sandy
mucks 100, and peats -140. A complete discussion of soluble
salts, symptom of injury, and methods of testing in various
media mixtures can be found in the section on fertilization
under soluble salts.
When selecting organic materials for use in media mixtures,
the ratio of carbonaceous material (cellulose) to nitrogen in
the organic matter (C:N ratio) must be considered.
Rapid decay of organic matter can be a problem in media
mixtures containing bark, sawdust, shavings or other similar
amendments. The rate of decomposition depends on the amount
and type of organic matter, and on fertilization levels, particular-
ly the amount of available nitrogen. Mixtures high in organic
matter (except peats) which contain a high percentage of fibrous
material should be fertilized lightly and regularly with a nitro-
gen containing fertilizer to prevent nitrogen starvation of plants
while the organic matter is decomposing. Sawdust, for instance,
has a C:N ratio of about 1,000 to 1, while bark has a ratio of
300 to 1. This means that decomposition of 1 ton of sawdust
would require about 24 pounds of nitrogen (N) (about 70
pounds of ammonium nitrate), while 7 pounds of nitrogen
(about 20 pounds of ammonium nitrate) will decompose 1 ton
of bark. Not only is extra nitrogen needed when most organic
materials, except peat, are used in media mixtures, but the tim-
ing of these applications of fertilizer is important. The fertilizer
should be split into several applications so that the nitrogen will
not leach or be lost before microorganisms can use it in decom-
posing the organic matter.
This term may legitimately be applied to two different prob-
lem areas which may occur with media mixtures. The first is
shrinkage (volume loss) of the media mixture during mixing
which occurs when coarse and fine components are mixed to-
gether. As an example, Table 2 shows that a loss in volume of up
to 22.8% can occur when builders sand, native peat, and shav-
ings are mixed together. With builders sand and German peat
there is no shrinkage. This factor is important primarily from
the standpoint of cost, as more of each component is needed to
obtain the same final volume of media mixture.
Another use of the term shrinkage is that applied to the loss
through oxidation of organic components of a media mixture in
containers over a period of time. In media mixtures composed
of 75% to 100% organic material, a loss in volume (media mix-
ture inside container) of up to 50% may occur within a year.
Table 2. The mean chemical and physical characteristics of twenty-
seven potting media.
1 Builders sand (BS)
2 Shavings (Shv)
3 Perlite (Per)
4 German peat (GP)
5 Native peat (NP)
Ratio (% volume)
1 Cation exchange capacity (C.E.C.) is a measure of the media's ability to
hold fertilizer nutrients against leaching, and is measured in milliequiva-
lents per 100 grams of dry soil. C.E.C. readings appear low because they
were determined on the standard media particle sizes without first pul-
2 Water-holding capacity is percentage by volume of water, based on dry
weight of soil, remaining in the soil after gravitational water has drained
This shrinkage must be considered when selecting media com-
ponents, because these losses decrease plant growth and require
addition of potting medium to plant containers before they can
be marketed, which costs money. Addition of medium on top of
the root ball may be harmful to the plant. When severe shrink-
age occurs, the consumer receives a less desirable plant because
of the smaller root ball. Loss of medium or shinkage through
oxidation can be reduced by decreasing percentage of organic
components in media mixtures or maintaining higher moisture
levels within the nursery.
FREEDOM FROM PESTS
When selecting media components, freedom from disease-
producing organisms, insects, nematodes, weed seed, and con-
taminants such as weed killers and other materials which can
influence plant growth must be considered. Materials such as
German peat, sand, shavings, and perlite generally do not need
sterilization, while native sands, muck, and peat should always
be treated. Even where diseases, insects, or nematodes are not
a problem, sterilization for weed control alone is valuable. There-
fore, when considering costs of media mixtures, the cost asso-
ciated with sterilization needed for a particular component must
A good grade of medium grained sand is an important non-
organic constituent of most media mixtures used in Florida. Al-
though many growers use local sands (sandy soils) this is not
the best policy, as most are too fine for proper drainage when
placed in containers, even though they have been satisfactory
in the field. In addition, they must be sterilized for control of
pests, which generally increases their cost above that of builders
sand. Generally, best results can be obtained with medium grades
of washed builders sand combined with organic components.
Perlite is a volcanic rock that is expanded up to 13 times its
original volume when heated to about 18000F, which results in
popcorn-like particles. It is very light, weighing 6 to 9 pounds
per cubic foot, and it holds about 3 to 4 times its weight in
water. Perlite is neutral to slightly alkaline in reaction, having
a pH of 7.0 to 7.5, and is available in particle sizes ranging from
that of large river-bottom sand to that of small gravel. This is
an ideal range to make organic material more friable for good
aeration. This material is essentially chemically inert, and pro-
vides no toxic substances in the mix and no elemental material
that would cause problems in fertilizer programs. When pur-
chased, it is usually sterile, and is an excellent material as a
medium component to provide for lightness in weight and aera-
tion qualities. Since it is always uniform it is more desirable
than other mineral components, but has low nutrient holding
capacity like sand.
A number of calcined clays are on the market with quite
different characteristics. For example, Turface has a high cation-
exchange capacity, and Terragreen a low one, while both have
low water- holding capacities. Although these materials are ex-
cellent media components for inclusion in a potting mixture,
their high cost limits their use except in special mixtures. Cal-
cined clays are sometimes used to supply nutrients and some
water-holding capacity when organic materials are not desired
in the mixture.
This is a heat-expanded mica or clay material that initially
is porous, and has high water and nutrient-holding capacities.
Its bulk density ranges from 6 to 10 pounds per cubic foot, with
finer grades of the material having the higher densities. Vermi-
culite has approximately half the nutrient- and water-holding
capacities as good grades of imported peat.
One of the major problems with vermiculite is that once
compressed or compacted it loses its ability to re-expand. With
use, therefore, it often becomes so compacted that it impedes
drainage and aeration. Because of this it is not highly recom-
mended as a media component.
A controversy concerning use of imported peats versus native
peats has raged in Florida for years. Both native and imported
peat are satisfactory organic amendments for media mixtures,
but each has certain advantages over the other.
Imported sphagnum peat moss is generally of high quality
with good fiber content and does not decompose as rapidly as
native peat. In addition, it is generally free of pests and, there-
fore, does not require sterilization prior to use in nursery pot-
ing media. However, cost per cubic yard is considerably higher
than native peat, and additional labor is required to shred and
Native peats are very variable, usually with low fiber con-
tent, and require sterilization for control of weeds and soil-
borne pathogens. However, on a cubic yard basis they cost ap-
proximately half that of imported peat. Another advantage of
native peat is availability and ease of mixing, since it is moist
and shredded at time of delivery. Recent research indicates that
Oxford and Peace River peats from Florida have fairly good
fiber content, and they produce nursery stock equal in quality
to imported peat.
Shredded or milled pine bark having particle sizes predomi-
nately ranging from 1/8 to 3/8 inches appears excellent as a
substitute for peat in growing media. Peats of the proper types
are becoming difficult to obtain. They are costly and quite vari-
able, although they have so many desirable characteristics for
amending mineral soils that they have been considered the
standard of excellence for years. Pine bark has most of the fine
qualities of a peat media amendment, and has been readily avail-
able at reasonable costs as a by-product of the pulp wood industry.
Pine bark has the added advantage of being quite uniform re-
gardless of the area of production. It is low in soluble salts and
Bark has approximately the same bulk density and nutrient
holding capacity as peat, slightly less water holding capacity,
and a higher carbon:nitrogen ratio. The C:N ratio is important
because it partly determines the amount of nitrogen required in
decomposition of the material. Peat has a relatively low C:N
ratio, and it decomposes so slowly that additional nitrogen in
excess of plants' needs is not required for decomposition of peat.
Bark, on the other hand, has a slightly higher C:N ratio, and
its initial decomposition rate is faster than peat. Therefore,
approximately 1/ to 1, pounds actual nitrogen per cubic yard
should be added to a 1:1 by volume mixture of sand and bark
at time of mixing to compensate for the extra utilization of nitro-
gen by soil microorganisms in initial decomposition of the bark.
The lasting qualities of bark compare favorably with peat.
This material has such high water retention qualities that
the potting medium tends to become water-logged when it is
used in high concentrations in the medium. It also has relatively
high nutrient holding capacity, but a major disadvantage of saw-
dust is its high C:N ratio and rapid decomposition rate. The high
C:N ratio and rapid decomposition rate means that high levels
of nitrogen, above the amount required for regular plant nutri-
tion, must be added to the medium to supply the soil microor-
ganisms in the decomposition process. If high amounts of saw-
dust are added to a medium, it is almost impossible to supply
enough nitrogen for plant growth and microorganisms, and plants
show symptoms of nitrogen deficiency. Sawdust is among the
least desirable organic materials to add to a growing medium,
but in areas where it is available in very large quantities and is
very cheap, nurserymen are tempted to use it. When sawdust is
used, it should not comprise more than one-fourth by volume
of the total medium.
SHAVINGS AND WOOD CHIPS
These materials are of the same wood product as sawdust,
except in larger particle size. They have less water and nutrient
holding capacities than sawdust because of the larger particle
sizes, and where used, other organic materials such as peat must
also be added to give these qualities to the medium. They do
allow for aeration. They also have a very high C:N ratio, but
due to larger size of particles which reduces exposed surface
area, the rate of decomposition is slower than sawdust. There-
fore, they do not present the same problems of nitrogen de-
pletion. Wood chips are often too large to mix well in the
medium, and often reduce water holding capacity of the total
medium to an unsatisfactory level. Where either of these materi-
als is used as a media component, it should not comprise more
than one-fourth of the medium by volume.
Sugarcane pulp (bagasse), a by-product of the sugar indus-
try, is available in Florida and some other southern states. This
organic material can be used as a media amendment where avail-
able, but requires addition of nitrogen because of its high
carbon: nitrogen ratio. Bagasse, properly aged, is usually more
expensive than peat and is not as desirable.
Limited research with rice hulls has shown that up to 25%
by volume in a media mixture is acceptable, but not as satisfac-
tory as other organic media amendments.
Unless a price advantage can be obtained over other organic
components, rice hulls are not suggested for use in potting mix-
MUCK AND SANDY MUCK
Throughout much of southern Florida large quantities of
muck are used as the potting medium for container production
of woody ornamentals. This practice has developed primarily
because of low cost and availability of these materials and be-
cause they do produce satisfactory plants most of the time.
Mucks are peats that are oxidized to the point where no
fiber remains. They are very fine and very variable in composi-
tion, which is affected by source and depth of mining these ma-
terials. Therefore, reproducibility of media mixtures using mucks
is usually impossible.
Where mucks have a decided cost advantage they may be
used as the container mixture, but growers should be aware of
their disadvantages, which include variability in percent organic
matter presence of weed seeds and disease pathogens and rapid
oxidation in containers (shrinkage). Mucks should be amended
before use with materials listed in the fertilization section to
prevent possible nutrient deficiencies.
MEDIA MIXING METHODS
Proper mixing of growing media is an important factor in
production of quality ornamentals. When various media com-
ponents are mixed together, a homogenous mixture must be ob-
tained to achieve maximum benefit from the various components.
This includes fertilizer amendments as well as media compo-
Variabilty in media mixtures will cause uneven plant growth
from container to container because cation exchange and water
holding capacities will vary. These factors will cause variable
nutrient levels from container to container, and differences in
plant response within the container bed will be considerable.
Proper mixing of fertilizer amendments such as calcium, mag-
nesium, phosphorus, and micronutrients is just as important,
because the same response will occur. In the discussion that fol-
lows, the principal methods of mixing nursery potting media are
discussed along with their associated problems.
The best mixing is provided by the cement mixer commonly
utilized on ready-mix trucks. These mixers can be obtained new
or used and placed on stationary bases where they are normally
loaded with a mechanized hopper which is loaded with tractor
front-end loaders. Mixing of media components and nutritional
additives is most satisfactory when done in this type mixer.
A mixer-pasteurizer has been developed by the Florida Co-
operative Extension Service which simultaneously does a good
mixing and pasteurizing job. This equipment is discussed in the
section on mechanization.
Many growers use shredders to shred peat and other organic
substances, and mix in fertilizer amendments at the same time.
This system of mixing does not provide a homogenous media
mixture because the various particles segregate. Addition of
micronutrients is also unsatisfactory when they are added in
this manner, because mixing is not complete, and when the
media is placed in pots large variations will occur between pots.
Some nurserymen utilize front-end loaders to mix media by
lifting and dropping the various components in a pile. This sys-
tem is simple and inexpensive, but does not provide satisfactory
mixing, especially of fertilizer amendments. Where possible, this
system should be replaced with a mixer or shredder operation.
SUGGESTED MEDIA MIXTURES
The decision to use a particular media mixture depends on
the many factors discussed in this section. However, in the final
analysis growers most frequently select materials that are lowest
in cost and most readily available. Hopefully, this discussion
provides the information necessary to combine materials selected
so as to provide a media mixture that will grow quality plants.
Media mixtures composed of two or three components supplying
desired physical and chemical properties may be used. Generally
three-component mixtures are most satisfactory from the cost
standpoint, since more low cost materials may be included. How-
ever, this necessitates better mixing equipment and a larger
storage area. Tables 3 and 4 list suggested mixtures in decreas-
ing order of desirability.
As previously stated, the function of a medium is to provide
an adequate foundation or base for root growth that will give
the plants stability, a high moisture environment while allowing
free drainage, ample aeration, and high nutrient capacity with
minimal decomposition and shrinkage. To obtain all of these
characteristics more than one material must be used in a media
mix. Usually two materials are sufficient to obtain the proper
root environment, but occasionally three materials are desirable
for varying reasons. More than three materials are not generally
recommended because of the economics of mixing with uniform
Table 3. Materials suggested for two-component potting mixtures
for container nursery stock listed in decreasing order of de-
1. Imported peat Builders sand
2. Native peat Builders sand
3. Ground pine bark Builders sand
4. Muck Native sand
1 Depending on particle size of materials used, the percent of organic
components can vary between 50% and 75%. As a starting point, use
60% organic and 40% sand and adjust if necessary.
2 Native sands with particle sizes of .002 to .02 inches in diameter may be
substituted but are less desirable.
Table 4. Materials suggested for 1:1:1 by volume potting mixtures
for container nursery plants listed in decreasing order of
Organic Organic or inorganic Inorganic
component' component component2
1. Imported or native peat Perlite Builders sand
2. Imported or native peat Bark Builders sand
3. Imported or native peat Shavings Builders sand
1 Depending on particle size of materials used, the percent of organic
component can vary between 50% and 75%. As a starting point, use
60% organic and 40r, sand and adjust if necessary.
" Native sands with particle sizes of .002 to .02 inches in diameter may be
substituted but are less desirable.
consistency and because it is unnecessary to do this in order to
obtain requirements of a good medium.
The mixing of two materials is most desirable, and the above
mentioned characteristics can be obtained by mixing imported
peat, high quality native peat, or shredded pine bark with sand
of the proper particle size in approximately 1:1 volume mixtures
Where three items are to be utilized in the mix, suggested
materials and rates are given in Table 4.
Selection of containers is very important because they have
an enormous effect on sales appeal, plant growth, and shipping
ease. Cost of the containers adds significantly to production costs,
and durability is important especially when an excess of some
plant material occurs and plants have to be held.
Product attractiveness is an important consideration when
plants are sold directly to consumers or to retail outlets, since
rusty, damaged, or otherwise unattractive containers have less
sales appeal. This factor is less important when plants are sold
primarily to landscape contractors since the ultimate consumer
rarely sees the containers. In general, attractively packaged or-
namentals, as well as other products, always sell better than
poorly packaged products.
Growth is affected by container size, but growth reduction
may also be due to poor drainage and poor aeration caused by
insufficient drainage holes. A container color can also reduce
growth if it allows the build-up of excessive heat within the
medium when sunlight falls on the container walls.
Research (31) has shown that container plant size is con-
trolled to a large extent by fertilization level provided, but that
quality landscape size plants can only be produced in the larger
size containers. Minimum acceptable landscape size plants can
be grown in 6-inch containers (generally called one gallon) or in
larger sizes. Plants grown in smaller size containers are generally
unsatisfactory unless great care is given during the establish-
Drainage of containers is very important since a "perched"
water table exists within a container's restricted growing area
and/or volume. Drainage holes should be located on container's
side and not on the bottom, since holes on the bottom are easily
plugged. The number and size of holes should be in proportion
to size of the container so proper drainage can occur. One gallon
containers should have at least four holes of about 1/. inch in
diameter; 2-gallon containers should have at least four holes of
about 3/% inch in diameter; and 3-gallon containers should have
at least four holes of about 1 inch in diameter.
Container color has been associated with growth for several
years, since it was observed that plant roots were damaged in
certain containers. Recent research (14, 46, 94) has shown that
soil temperature inside containers of black or dark green color
was 5 to 100F higher than for light colored ones when the sun
was shining on the side where temperature was recorded. There-
fore, it was concluded that damage noted (mostly in plastic
containers, but sometimes in metal containers painted a dark
color) is due to lethal root temperatures immediately inside the
wall of the container. With spacing of containers, which allows
sunlight to shine on container walls, it is suggested that contain-
ers of lighter color be used (white, silver, or light green).
The life of containers is variable due to materials used in
their manufacture and presence or lack of paint on metal cans.
Metal cans are subject to rusting due to the high moisture levels
and corrosive chemical fertilizers used. In general, metal cans
that are not painted will last about one year, while those that are
painted last about two years. Plastic containers, on the other
hand, are not affected by fertilizers or moisture, but by sunlight.
Therefore, there is no way to determine durability of plastic
containers by observation since this is determined by type of
plastic used by the manufacturer. However, plastic containers
from larger well-known suppliers generally have a life expec-
tancy of up to 2 years. The main problem with plastic containers
is breakage which may occur when they become older and brittle,
and this is aggravated by cold weather.
STACKING AND SHIPPING
Stacking of containers during shipment can be very impor-
tant if shipping is done by a nursery. Metal containers usually
stack and ship better than plastic. However, some of the heavier
plastic containers will also stack if plastic deterioration has not
begun. Two container shapes are available, round and square.
Shape is relatively unimportant in nursery situations, since spac-
ing is usually greater than container size. However, shape can
be very important during shipping. Square containers are more
conservative of space when stacking is not practiced; however,
they cannot be stacked due to lack of space between plants. If
stacking is practiced during shipping, round containers are more
conservative of space since they allow stacking.
For many years No. 10 food cans and egg-cans were the
standards of the nursery industry, and are still used by many
nurserymen, either unpainted or painted. These containers left
unpainted have little sales appeal, but when painted they have
appeal almost equal to manufactured metal cans. Plants grown
in No. 10 food cans, and other straight-sided cans like egg-cans,
may have to be cut out with a can-cutter. Many nurserymen
paint No. 10 food cans and egg-cans with a mixture of tar,
kerosene, and paint using a 2:8:1 parts by volume mixture.
Manufactured metal containers are very popular and have
great sales appeal.They are available in almost any size desired
and have good durability and stacking characteristics. Since they
have tapered sides, plants can be removed easily without aid of
Many different types of plastic containers have appeared on
the market since their introduction, and many have proved to be
unsatisfactory under full sun conditions. Ultraviolet light causes
deterioration of plastics, and inhibitors have to be placed in the
plastic to retard breakdown. Addition of inhibitors increases
container cost, and this plus lack of information on breakdown
rates of the materials used in nursery containers caused poor
initial acceptance. However, companies remaining in business
are now providing plastic containers that have a life expectancy
that compares well with metal containers. Light colored plastic
containers with adequate drainage holes provide conditions for
good plant growth. Plants can also be removed easily from most
plastic containers without a can-cutter because they have tapered
In years past some nursery plants were grown in clay con-
tainers, but with introduction of metal and plastic cans this
practice proved too costly.
Various types of small peat containers are available which
are used satisfactorily in propagation of plants, but none are
satisfactory for production of gallon sized woody ornamentals.
OTHER TYPES OF CONTAINERS
There are a number of containers on the market made of
combinations of wood, peat, and other fiber mixtures. These con-
tainers are acceptable for short-term crops that remain in the
container only 3 to 4 months. They have proved excellent for
growth of dormant rose stock, for example.
A number of speciality containers are used in the trade.
These include tar paper with a plastic cover, styrene, aluminum,
etc. Each of these containers has some merit, but they are not
commonly available and are generally used for special purposes.
Fertilization of container grown plants is an important pro-
duction factor because of the effect of fertilization on growth,
quality, and cost of production. The ideal fertilization program
would be one that is easy to execute, and would consistently pro-
duce high quality plants at a reasonable cost.
SOIL OR MEDIA REACTION pH
Soil or media pH generally affects plant growth indirectly,
provided chemicals producing extremes in soil reaction are not
toxic to the plant. The pH affects the solubility and retention in
the soil or media of the nutrient mineral elements. This in turn
affects availability to the plant of nutrient elements, especially
the microelements. The pH also affects beneficial soil micro-
A satisfactory media pH range is from 5.8 to 6.2. A pH of
6.0 is best from the standpoint of solubility of elements, less
danger of injury from toxic elements such as aluminum, and
greatest activity of the soil microorganisms that convert am-
monium (NH4) to nitrate nitrogen (NO:).
As acidity increases (that is, as pH decreases below 6.0),
especially in potting media low in organic matter, the solubility
and leaching rates of base elements such as calcium, magnesium,
and potassium increase. As soil reaction becomes even more acid
(below pH 5.5), there is considerable increase in the leaching
rates of phosphorus and ammonia. Aluminum, which is toxic to
plants, is more available as soil or media reaction becomes more
acid, and there is considerable evidence that growth retarding
effects of very acid soils may be due, in part, to aluminum
In summary, pH effects certain soil microorganisms, leaching
of elements, and increase in possible injury to plants by toxici-
ties or deficiencies by affecting nutrient availability and solu-
bilities. Thus the desirability is apparent of adjusting pH to the
range of 5.5 to 6.5, where such problems are less operative.
FERTILIZERS AND FERTILIZATION
Florida Cooperative Extension Bulletin 183 (1971) by Gay-
lord M. Volk contains extensive information on this important
subject. Volk states, "There is a wealth of information on the
Florida fertilizer tag. This information if understood by the
grower can often prevent needless expenditure for materials
containing unnecessary elements or plant losses resulting from
the use of materials lacking in some essential plant food." How
to read a fertilizer tag and other pertinent information on fer-
tilizer materials, helpful to Florida nurserymen growing woody
ornamental plants, is given in Volk's bulletin.
Essential composition of fertilizers is given on the fertilizer
tag as percentages (1% equals one unit which equals 20 pounds).
Nitrogen and sulfur are expressed as the element, while phos-
phorus (phosphoric acid P205), potassium (potash K20),
calcium, magnesium, copper, zinc, manganese, iron, boron, and
molybdenum are listed as oxides (Table 5).
Table 5. Composition, method of expression, and percentage of the
element in materials listed on a fertilizer tag.
Shown on Percentage
Fertilizer Chemical tag as percentage of element
element symbol of1 in oxide
Nitrogen N N
Sulfur S S
Phosphorus P P2,O 43.7-P
Potassium K KO 83.0-K
Calcium Ca CaO 71.5-Ca
Magnesium Mg MgO 60.3-Mg
Copper Cu CuO 79.9-Cu
Zinc Zn ZnO 80.3-Zn
Manganese Mn MnO 77.4-Mn
Iron Fe FeO, 69.9-Fe
Boron B BO 31.0-B
Molybdenum Mo MoO, 66.7-Mo
1 Except for nitrogen and sulfur, which are expressed as the element.
Those essential elements needed by plants in relatively large
amounts (nitrogen, phosphorus, potassium, calcium, magnesium,
sulfur) are commonly called major elements, while elements re-
quired in relatively small amounts (copper, zinc, iron, man-
ganese, boron, molybdenum) are referred to as minor, sec-
ondary, or trace elements. These descriptive terms are somewhat
misleading, because the nutritional role of copper, zinc, or iron
is just as important as those of major elements such as nitrogen,
potassium, phosphorus, or calcium. For this reason the more
accurate terms of macronutrients for major elements and micro-
nutrients for the minor, secondary, or trace elements are used
Numerous experiments have shown that nitrogen is used in
large amounts by plants, and is the most important factor af-
fecting size and quality of container grown woody ornamental
plants. This emphasizes importance of proper management of
the nitrogen supply (17, 32, 33, 37, 38, 42, 45, 65, 66) (Fig. 4).
Nitrogen deficiency of container grown woody ornamental
plants is evidenced by stunted new shoot growth, with leaves
over the entire plant becoming pale green to yellowish-green in
color (Fig. 5). Plants grow slowly, if at all, until nitrogen is
supplied. Nitrogen deficient plants are more susceptible to cold
injury than those adequately supplied with nitrogen, and flower
bud opening is delayed on most species of flowering plants.
Two forms of nitrogen, nitrate and ammoniacal, are used by
plants. Nitrate nitrogen is immediately available to plants, but
is loosely held by the soil particles against leaching, and is
readily lost from media by excess water from irrigation or rain-
fall. Ammoniacal nitrogen is used readily by plants, and is less
subject to leaching than the nitrate form because it is held by
the exchange complex. Ammoniacal nitrogen is usually converted
to nitrate nitrogen by bacterial action in from one to four weeks,
depending on factors such as soil reaction, temperature, and
Urea, a synthetic organic nitrogen, is an important nitrogen
source frequently used in mixed fertilizers (Table 6). Urea is
converted into ammonium by microbial activity in a few days
after application, and is further converted into nitrate nitrogen
if conditions are favorable. Slow release forms of urea, urea-
form, or ureaformaldehyde are available. (See section on slow
Important points to be considered in selecting nitrogen source
materials are cost per unit of nitrogen, availability, other essen-
tial elements a given material may contain, type of application
desired, and cost of application (dry versus liquid fertilization).
Nitrogen may be supplied by several slow release fertilizers
which are discussed in the section on this subject. Some common
nitrogen sources are ammonium nitrate, potassium nitrate, am-
Figure 4.-Effect of nitrogen on growth of Buxus microphylla japonica.
Treatment started on 1-15-72; photograph taken 9-26-72. Both plants re-
ceived superphosphate, dolomite, and "Perk" (commercial microelement
mixture) at rates of 5, 8 and 4 lb/cu/yd of meduim, respectively, and po-
tassium was applied monthly at rate of 1,000 lb/A/yr. Plant on left re-
ceived no nitrogen, plant on right given nitrogen monthly at rate of 1,000
Figure 5.-Normal and nitrogen deficient 'George Lindley Taber' azalea
plants. Left, normal plant. Right, symptoms evidenced as over-all yellowing
of leaves over the entire plant.
monium sulfate, calcium nitrate, sodium nitrate, urea, and mono-
ammonium and diammonium phosphate (Table 6).
Nitrogen fertilization rates ranging from 800 to 1500
lb/A/yr and a 2:1 ratio of nitrogen to potash are recommended
for container grown woody ornamental nursery plants (Table
The importance of phosphorus for growth of plants has long
been established. Symptoms attributable to phosphorus deficiency
have not been identified on container grown woody ornamental
plants in Florida nurseries, possibly because of high phosphorus
application rates generally used by nurserymen.
Many commonly used components of potting media are low
in phosphorus, and the plant's phosphorus needs increase as
nitrogen and potash rates are increased. In media high in or-
ganic materials, such as undecomposed sawdust, some phos-
phorus is used by microorganisms involved in its decay (17)
and is removed from availability to plants.
Choice of a phosphorus fertilizer should be based on cost per
unit of P205 (available phosphoric acid), consideration of other
essential or nonessential elements it may contain, and applica-
tion method used by the nurseryman. Phosphorus sources in-
clude ordinary and treble (triple) superphosphate, ammoniated
superphosphate, and diammonium and monoammonium phos-
phates (Table 6).
Superphosphate is an excellent phosphorus source material
when fertilizer is applied dry. Cost of application and cost per
unit of phosphate are low, and cost is further reduced when
superphosphate is mixed into potting media as the media are
prepared. Superphosphate will supply phosphorus to plants for
an entire growing season, if media pH is maintained at about
5.5 to 6.5. However, considerable phosphorus may be lost by
leaching if the medium is too acid (continuously below pH of
about 5.5). When low pH conditions occur phosphorus should
be applied again in about 6 months. Superphosphate contains,
in addition to phosphorus, the essential elements calcium (19-
22('), sulfur (10-12% ) as gypsum, and small amounts of molyb-
denum. It also contains fluorine, which will injure the foliage of
some species. Treble superphosphate is as effective as super-
phosphate in dry fertilizers and costs less per unit of phosphoric
acid, but a lot of the gypsum (calcium sulfate) has been re-
Table 6. Chemical content and salt index of several fertilizer materials1.
Percentage composition2 Salt
Chemical N KO PO,0 MgO CaO S Other index3
Nitrogen source materials
Ammonium nitrate 33.5 105
Calcium nitrate 15.5 36.0 53
Potassium nitrate 13.8 46.6 74
Sodium nitrate 16.2 100
Ammonium sulfate 20.5 -69
Monoammonium phosphate 12.2 61.7 30
Diammonium phosphate 21.2 53.8 -34
Urea 46.6 -75
Potassium source materials
Potassium chloride 50.0 109
Potassium chloride 60.0 116
Potassium nitrate 13.8 46.6 -74
Monopotassium phosphate 34.8 52.2 8
Potassium sulfate -54.0 18.4 46
Sulfate of potash-magnesia 21.9 18.0 22.0 43
Phosphorus source materials
Monoammonium phosphate 12.2 61.7 30
Diammonium phosphate 21.2 53.8 34
Monopotassium phosphate 34.8 52.2 8
Superphosphate 20.0 23.0 9.0 8
Superphosphate, triple 45.0 20.0 2.0 10
Table 6. Chemical content and salt index of several fertilizer materials1.
Percentage composition Salt
Chemical N KO P,Os MgO CaO S Other index3
Magnesium source materials
Dolomite 21.8 30.5 1
Magnesium sulfate 16.3 13.0 44
Sulfate of potash-magnesia 21.9 18.0 22.0 43
Lime source materials
Dolomite 21.8 30.5 1
Lime calcium carbonate 56.5 5
Superphosphate 20.0 23.0 9.0 8
Gysum 30.0 16.0 8
Copper sulfate 12.0 30.00 CuO -
Zinc sulfate 12.0 45.0 ZnO -
Manganese sulfate 13.0 30.0 MnO -
Iron chelate 8-17 Fe.O, -
1 L. F. Rader, Jr., L. M. White, and C. W. Whittaker. 1943. The salt index-a measure of the effect of fertilizers on the con-
centration of the soil solution. Soil Sciences 55: 201-218.
2 By "percentage composition" is meant percent N and S, respectively, in nitrogen and sulfur carriers, and oxides of the other
nutrients (P, K, Ca, Mg, Mn, Cu, Zn, Fe-Table 1) in their respective carriers.
3 Salt index compared against equal weight of sodium nitrate which was assigned a value of 100.
When liquid fertilization is used, phosphorus may be supplied
from diammonium (21% nitrogen) or monoammonium phos-
phate (12/o nitrogen). In addition to phosphorus these mate-
rials supply part of the nitrogen needs of the plants. Phosphorus
from these sources should be applied every 2 to 3 months, de-
pending on medium, pH, rainfall, and season of the year. The
plant's phosphorus requirements, for the first season, may be
more economically supplied by mixing superphosphate in media
when prepared than by using more expensive diammonium or
A ratio of nitrogen to phosphorus to potassium of 4:1:2, with
the amount of phosphorus applied based on nitrogen and potas-
sium levels used, will supply the phosphorus requirements
This nutrient element is used by plants in quantities second
to nitrogen. Potassium affects size and quality of plants and
must be applied repeatedly in the fertilizer to container grown
plants. In experiments low potassium levels (50 to 120
lb/A/yr) combined with relatively low nitrogen levels (60 to
400 lb/A/yr) provided enough potassium to prevent growth
limitation, and plants did not respond to higher potassium levels
(42, 65, 66, 89). However, higher nitrogen levels (600 to 1500
lb/A/yr) combined with higher potassium levels (160 to 400
lb/A/yr) produced plants of increased size and quality. There
was a reduction in size and quality when plants were fertilized
with combinations of high nitrogen and low potassium levels
Increasing nitrogen often will produce potassium deficiency
when potassium is at or near deficiency levels in plants that
previously showed no visual potassium deficiency symptoms, or
it will increase severity of symptoms already present (38, 41).
Visual potassium deficiency symptoms have not been ob-
served on container grown woody ornamental plants in Florida
nurseries. Two plant species have developed potassium deficiency
symptoms in experiments at Gainesville (38, 41). 'Formosa'
azalea leaves developed small necrotic spots which increased
rapidly in size until much of the area died. Symptoms first ap-
peared on basal leaves of lower shoots and progressed towards
the tips of shoots, but even on severely affected plants tufts of
leaves at shoot tips remained green (Fig. 6). These symptoms
were different from leaf chlorosis and marginal scorch, with
dead areas progressing inward from the margins, that charac-
terize potassium deficiency on many plants. Potassium deficiency
on container grown wax-leaf privet was typical of that described
for several other plants. Basal leaves on lower branches of wax-
leaf privet first showed symptoms which appeared as mild chlo-
rosis at tips and margins of leaves. Chlorotic areas extended
downward, especially along margins, until three-fourths or more
of the leaf margins became chlorotic in advanced stages. Only
basal portions remained green. Dead areas increased in size and
number as severity of deficiency increased. When the deficiency
became acute, basal leaves dropped from some shoots, leaving
portions of affected branches bare.
Materials used individually or with other fertilizers to supply
potassium to container grown plants include potassium sulfate,
potassium chloride, potassium nitrate, and sulfate of potash-
magnesia (Table 6). Choice of potassium source fertilizers
should be based on cost per unit of potash, other essential or
nonessential elements Ihey contain, and their salt index. For
example, potassium nitrate contains 46.6% potash and 13.8%
nitrogen, and sulfate of potash-magnesia contains 22% potash,
18% MgO, and 229 sulfur, all elements essential to plant
growth. Slow release potassium frit is not recommended because
of its cost and because considerably more of it is needed than
the readily soluble materials to supply needed potassium to
Figure 6.-Normal and potassium deficient 'Formosa' azalea plants. Left,
normal plant. Right, plant showing large necrotic spots on basal and mid-
shoot leaves with normal leaves at shoot terminals, and abscission of some
plants. Its slow release rate increases the risk of developing
potassium deficiency (38, 41).
A 2:1 ratio of nitrogen to potash will supply potassium re-
quirements of container grown woody ornamental plants in
Florida. Potassium fertilization rates should range from 400 to
800 lb/A/yr depending on nitrogen level supplied (Table 9).
This essential element is used in comparatively large amounts
by woody plants, but identifiable symptoms of calcium deficiency
have not been observed on container grown woody ornamental
plants in Florida nurseries. This is probably due to extensive
use by Florida nurserymen of dolomite to adjust pH of their
potting mixtures, use of superphosphate as a source of phos-
phorus, and use of water high in calcium.
Calcium deficiency symptoms of woody plants described in
the literature are largely from plants grown in sand or solution
Calcium deficiency symptoms have developed on experimental
container grown viburnum plants at Gainesville (34). Chlorosis
appeared first, developing as an interveinal chlorosis on young
maturing leaves at shoot tips, and later on older leaves as green-
ish-yellow inverted U-shaped areas, which usually enlarge to
cover most of the surface. Chlorotic leaves at shoot tips often
developed leaf roll, which was evidenced by edges of leaves
curling upward until, in severe cases, they touched or overlapped.
A red to reddish brown discoloration developed frequently on
both green or chlorotic leaves. Dead twigs, tip and marginal
burn, and dead spots developed on some leaves of affected plants.
Leaf drop occurred, and included mature leaves and young de-
veloping leaves at shoot tips. Severe leaf drop occurred in some
acutely affected plants. Chronic and acute calcium deficiency
caused severely reduced growth and death (Fig. 7).
Calcium-containing materials not only supply plants with
calcium, but also raise pH and reduce leaching from highly acid
soils of potassium, magnesium, phosphorus, ammonia (NH4),
manganese, zinc, iron, copper, and boron. Lime also reduces pos-
sible toxicity that may be caused by excesses of copper and alu-
minum. Increasing calcium content of media decreases avail-
ability of essential microelements manganese, zinc, iron, copper,
and boron, but increases molybdenum availability.
Calcium requirements of container grown woody ornamental
plants are most easily supplied by dolomite or other lime mate-
Figure 7.-Plant of Viburnum suspensum showing some typical symptoms
of calcium deficiency-chlorosis, leaf roll, necrosis, dwarfing, and formation
rials added to adjust media pH and by gypsum contained in
superphosphate (Table 6). Dolomite should be added to potting
media at rate of 7 to 10 pounds per cubic yard of mix (Table 9).
If use of dolomite and superphosphate does not raise calcium to
desired level in the media, ground limestone (calcium carbo-
nate CaC03) may be used to accomplish this. In certain areas
of Florida some ingredients used in media may be alkaline but
low in calcium. In this case the grower should not use additional
lime-containing materials, such as dolomite or limestone, that
raise pH of potting mixtures. Gypsum (calcium sulfate) at rate
of 5 to 7 pounds per cubic yard can be used in media without
This essential element, needed by plants in relatively large
amounts, is a chemical constituent of chlorophyll. Most ingre-
dients of potting mixtures are low in magnesium, but symptoms
are not common in Florida's ornamental nurseries. This may be
because growers make wide use of dolomite to adjust pH of the
media, because there is often magnesium in irrigation water,
and because less total magnesium is needed for normal growth
than the macronutrients nitrogen, potassium, and calcium
Recognizable magnesium deficiency symptoms have been seen
in Florida nurseries on container grown Japanese pittosporum.
Magnesium deficiency on this plant is characterized by a chlo-
rosis which develops only on mature leaves at the base of the
current season growth or on older shoots during the summer
and fall (Fig. 8). Unconnected chlorotic areas, irregular in size
and shape, develop in areas between midrib and main veins in
upper portions of leaves. These chlorotic areas enlarge and
merge to form large yellow areas with triangular-shaped green
areas at base of leaves. Some leaves lose all or most of their
green color, while tips of some leaves may remain green. No
symptoms have been observed on shoots or branches.
Difficulty of obtaining adequate magnesium intake, some-
times encountered with certain field grown woody ornamental
species (Japanese pittosporum, yew podocarpus, nagi podocar-
pus, poinsettia, and Canary Island date palm) in Florida is usu-
ally not a problem with container grown plants.
Magnesium requirements of container grown woody orna-
mental plants are usually supplied by magnesium carbonate in
dolomite used to adjust pH of the media. Add dolomite to potting
media at a rate of 7 to 10 pounds per cubic yard of mix (Table
9). Magnesium may also be supplied from magnesium sulfate
(epsom salts) or sulfate of potash-magnesia (Table 6). Mag-
nesium ammonium phosphate (MagAmP) costs considerably
more per unit of magnesium oxide (MgO) than does dolomite or
This essential element is needed by plants in about the same
quantities as phosphorus. Sulfur deficiency symptoms have not
been observed on container grown woody ornamental plants in
Florida nurseries. Apparently enough sulfur to prevent defi-
ciency symptoms is supplied by superphosphate and sulfate in
fertilizers, in irrigation and rain water, and from breakdown of
organic matter in potting mixtures (Table 6).
Sulfur deficiency symptoms described on woody ornamental
plants are almost entirely from plants grown in sand or solution
culture. Generally sulfur deficiency symptoms are similar to
those produced by nitrogen deficiency, except symptoms first
Figure 8.-Advanced stages of magnesium deficiency on Pittosporum
tobira shoot. Chlorosis developed first on basal leaves of shoot and pro-
gressed towards the tip. Terminal leaves are normal.
appear as a light yellow-green color of young developing leaves
rather than on older leaves as with nitrogen. As sulfur deficiency
increases in severity, all leaves on the plant may become pale
This essential element, required by plants in very small
amounts, has previously been supplied in manures, as impurities
in fertilizers, in field soils used in potting media, and in copper
fungicide sprays. Container production utilizes synthetic potting
media composed of materials such as imported or domestic peats,
sandy mucks, sandy soils, builders sands, wood shavings, wood-
bark, sawdust, perlite, and vermiculite all potentially low in
copper, and copper deficiency may develop on plants growing in
Recent experimental work has identified copper deficiency on
container grown common camellia cultivars 'Tricolor', 'Elegans',
and 'Lady Clare'; Southern Indian azalea cultivars 'Formosa',
'Fielder's White', and 'George Lindley Taber'; furry jasmine;
Jasminum nitidum; wax-leaf privet; and Japanese pittosporum
(28, 29, 36). Copper deficiency has also been observed on these
plants growing in containers in commercial nurseries.
Foliage symptoms of copper deficiency of these plants include
dwarfing, chlorosis, cupping, tip and marginal burn of leaves,
and premature leaf drop. The most prominent shoot symptoms
of copper deficient plants are shortened internodes, multiple
buds, dieback of shoot tips, and severe stunting of affected plants
(Fig. 9). Young plants of some species, planted in a copper de-
ficient medium, may at first make good growth, then develop
symptoms after a few weeks, while other plants make little if
any growth after transplanting into such a medium (29).
A copper treatment for all newly potted plants (cuttings and
liners) in Florida ornamental nurseries is recommended. Copper
deficiency may be corrected or prevented by either soil or foliage
applications of copper. An easy method of applying copper is to
uniformly incorporate copper sulfate in the potting mixtures at
the rate of 1 ounce per cubic yard of mix (Table 9). Copper
sprays are as effective as soil applications in controlling copper
deficiency. Spray with basic (tribasic) copper sulfate at rate of
3 pounds to 100 gallons of water plus a sticker-spreader. In ex-
periments one soil or spray application of copper has controlled
copper deficiency of container grown plants for 5 years.
Figure 9.-Typical copper deficient (A) and normal (B) plants of 'For-
mosa' azalea. (A) Typical symptoms of copper deficiency--chlorosis, small
terminal leaves, tip burn and dwarfing.
High nitrogen levels may induce copper deficiency on plants
that show none or slight symptoms at low nitrogen levels (29).
Lime (calcium) reduces availability of copper so excessive cal-
cium in the media may also contribute to development of copper
Zinc deficiency is commonly found on several woody and
herbaceous plants (citrus, pecans, tung, peaches, plums, avo-
cado, loquat, corn) in the field in Florida, but symptoms similar
to those of zinc deficiency have been observed only on container
grown loquat and dogwood in Florida nurseries.
Zinc deficiency symptoms first appear on young developing
leaves at shoot tips. Affected leaves show various degrees of
chlorosis and dwarfing depending on severity of the disorder.
Chlorosis develops between the veins on leaves of some species,
while on others chlorotic areas are not delimited by the veins.
Leaves of some species may develop wavy margins, while others
do not. Shortening of internodes produces rosette, a character-
istic symptom of zinc deficiency on several plants. Necrotic
symptoms are evidenced as dead spots which develop at random
Figure 10.-Zinc deficient i~
loquat plant showing severe -
symptoms. Leaves on upper .
portion of plant are abnor- ; s.
mally small, and show chlo-
rosis and necrosis. Some de-
foliation has occurred.
over leaf surfaces, premature leaf fall, and dead terminal shoots
Many commonly used ingredients of container potting media
are low in zinc; therefore, zinc should be applied to all container
grown woody plants in Florida ornamental nurseries. Zinc de-
ficiency may be prevented or corrected by soil or foliage appli-
cations of zinc. Probably the best application method is to uni-
formly mix finely ground zinc sulfate in the medium at rate of
1 ounce of zinc sulfate per cubic yard of mix (Table 9). If zinc
was not incorporated in the medium, apply it to plants as a
spray soon after containers are placed in the field (Tables 10,
Symptoms of this deficiency are common on several woody
ornamental plants in Florida landscape plantings, on both acid
and alkaline soils, but are not prevalent on container grown
woody plants in Florida ornamental nurseries. Occurrence of
manganese deficiency on container grown woody plants is
largely confined to areas where alkaline soil components may be
used as an ingredient of potting media.
Manganese deficiency first appears on young leaves at or
near shoot tips, and is evidenced as an interveinal chlorosis. The
amount of leaf area that is chlorotic and the intensity of yel-
lowing vary with age of leaves, plant species, and severity of the
deficiency. Severely deficient plants of some species show symp-
toms that cannot be distinguished from those of iron deficiency
on several other woody ornamental species in Florida. Leaves
and shoots of several affected species, except certain palm
species, are not materially reduced in size (Figs. 11, 12).
Manganese should be supplied to all container grown woody
ornamental plants to prevent development of maganese defi-
ciency. Probably the best application method is to uniformly mix
Figure 11.-Manganese deficiency symptoms. (A) Allamanda cathartica
shoots (left) showing interveinal chlorosis, (right) normal shoot.
Figure 12.-Manganese deficiency symptoms. Lagerstroemia indica shoots
(left) showing severe interveinal chlorosis and anthocyanin pigment, (cen-
ter) normal shoot, (right) moderate interveinal chlorosis.
finely ground manganese sulfate in the media at rate of 2 ounces
per cubic yard of mix (Table 9). If manganese was not mixed in
the media, apply it to plants as a spray soon after containers
are placed in the nursery bed (Tables 10, 11).
Iron deficiency symptoms are common on many woody orna-
mental plants in Florida landscape plantings, but are more
This element is required by plants for normal growth in very
small amounts. Molybdenum deficiency has been identified under
field conditions in Florida on Chinese hibiscus, citrus, and cauli-
flower. However, this deficiency has not been observed on con-
tainer grown woody ornamental plants in Florida nurseries.
Molybdenum deficiency symptoms described for a number of
plants are generally an interveinal chlorosis of leaves accom-
panied by a reduction in leaf size (citrus is an exception), ir-
regular wavy margins, and upward or downward cupping of
Molybdenum deficiency of Chinese hibiscus, found in land-
scape plantings, is commonly called strap-leaf in Florida. Symp-
toms develop on leaves at tips of growing shoots (106). In mild
stages leaves are slightly reduced in size and are deformed, while
severely affected leaves are greatly reduced in size, but there is
a greater reduction in width than length, producing the charac-
teristic strap-leaf appearance (Fig. 14). Compared with normal
leaves which are thin, smooth, and pliant affected leaves
are rough, thick and leathery, with midrib and main veins en-
larged and more prominent than those of normal leaves. A mild
chlorosis is evident on some young developing leaves, but affected
mature leaves are usually a normal green.
Superphosphate, frequently incorporated in the medium when
it is mixed or added later when dry fertilizer is applied (Table
9), contains small amounts of molybdenum. Application of lime
usually reduces occurrence of molybdenum deficiency on affected
plants. This deficiency can be corrected by both soil and foliage
applications of ammonium molybdate or sodium molybdate. On
basis of present information, molybdenum is not recommended
for inclusion in the potting media.
METHOD OF APPLICATION
Research and experience have shown that high quality woody
ornamental plants can be produced with a properly used dry,
liquid, or slow-release, fertilizer or with combinations of these
fertilization programs. Which method best suits a given nursery
operation depends on several important factors. These include
cost of fertilizer materials and cost of their application, size of
nursery operation, abilities of personnel applying the fertilizer,
and the nurseryman's personal opinions and desires as they re-
late to these problems.
Figure 14.-Molybdenum deficiency symptoms. Shoots of Chinese hibiscus
variety 'Brilliantissimus' (Single Scarlet). Left, normal; right, typical
molybdenum deficiency symptoms strap leaf, dwarfed, thick leaves with
irregular wrinkled or buckled margins, and prominent midribs and main
There are several factors to be considered in deciding upon
the chemicals to use for fertilizing container grown plants. The
cost per pound of available plant nutrients is the best single
"yard stick" for determining what fertilizer materials to use,
all other factors being equal. Solubility of materials determines
those that can be used in liquid fertilizer programs. Salt index
of the chemicals is another factor to be considered where high
fertilization levels are used over extended periods of time and/or
where growers have high levels of soluble salts in the irrigation
water. Under these conditions chemicals should be selected which
supply needed nutrient elements with a minimum salt residue
index (Table 6).
Slow release fertilizers
Good quality container grown plants can be produced with
single-element or multi-element coated slow-release fertilizers
as sources of the element or elements they supply, if rates and
frequency of application are adequate. Of the available single-
element slow-release materials, only nitrogen sources such as
urea-formaldehyde are recommended.
Duration of time that coated slow-release fertilizers are ef-
fective is affected by several factors: (a) surface placement
versus mixing in the media; (b) thickness of resin coating; (c)
temperature; (d) water and nutrient holding capacity of media;
(e) amount and frequency of rainfall and of irrigation; and
(f) level of fertilization.
Coated single-element nitrogen source materials (urea-for-
maldehyde, coated urea, encapsulated ammonium sulfate) and
multi-element coated slow-release 18-9-9 and 18-6-12 (Osmocote)
fertilizers were tested experimentally (32, 33, 38, 41). Compared
with soluble materials applied monthly, they produced plants of
equal size and quality only when the nitrogen supply for 6
months growing period (April 1 to October 1) was given in split
applications, the first mixed in potting medium at start of ex-
periment on April 1, the second applied to surface of containers
3 months later, July 1.
Some other multi-element slow-release materials containing
nitrogen, phosphorus, and potassium available on the market are
the "pill" and "root packets". If they are used, follow the manu-
Generally, coated slow-release fertilizers cost considerably
more per unit of plant food than soluble or dry fertilizers. Since
plants of comparable quality can be produced with any of the
methods discussed herein, the choice of which method to use
comes down to a grower's preference and a consideration of the
important cost factor. Cost of using coated slow-release mate-
rials should be weighed against cost of using liquid or dry fer-
tilizers (cost of fertilizer plus cost of application) in deciding
which method to employ.
Generally, recommendations for how often to fertilize con-
tainer grown plants are governed largely by their nitrogen re-
quirements and season of the year.
Research at the University of Florida has shown that ap-
plying ammonium nitrate as a liquid fertilizer every 4 weeks
was as effective in growing quality container grown viburnum,
'Formosa' azalea, Japanese pittosporum, and Japanese box, as
applications every 1, 2, or 8 weeks. Applying ammonium nitrate
every 8 weeks or 2 months was sometimes, but not always, as
effective in producing good quality plants as applications every
4 weeks or monthly (42, 43, 44). Experiments with viburnum,
Japanese pittosporum, and 'East Palatka' holly, using readily
available potassium sources potassium chloride and potassium
sulfate indicate that applications every 2 months were as
effective in producing high quality plants as were monthly appli-
cations (30, 32).
Changes in season produce changes in temperature and day
length which, in turn, affect rate of plant growth and, therefore,
the amount of nutrient elements they require. During colder
months of November, December, January, and February approx-
imately half as much fertilizer is required to maintain essential
elements at adequate levels in the plants.
Some factors affecting how much and how often to fertilize
are: (a) fertilizer requirements of plant species; (b) type ferti-
lizer used; (c) growth rate desired by the nurseryman; and
(d) changes in season which affect temperature and day length.
Experiments have shown that 800 lb/A/yr of nitrogen7 pro-
duced excellent quality 'East Palatka' holly plants, while wax-
leaf pivet, viburnum, 'Formosa' azalea, Japanese pittosporum,
and lantana responded to nitrogen levels up to 1,500 lb/A/yr.8
Growth is reduced during winter months of November,
December, January, and February, and fertilization rates and/or
frequencies should be reduced, especially in the northern half
of Florida. This can be done by using either (a) one-half of
rates listed in Tables 9 or 10, or preferably, (b) by using lower
range of these rates and omitting the November and January
applications. The same amount of fertilizer is applied during
these 4 winter months by both methods, but the second method
would save labor cost of two applications per year.
Recommendations on fertilizer materials to use, rates, and
7To obtain a rate of 800 lb/A/yr of nitrogen requires 2,400 lb/A/yr of
ammonium nitrate (33.5'/, nitrogen) or % teaspoon per gallon container
8To obtain a rate of 1,500 lb/A/yr of nitrogen requires 4,500 lb/A/yr of
ammonium nitrate (33.5r, nitrogen) or % teaspoon per gallon container
frequency of application are given in Tables 6, 9, 10, 11 and in
the section on fertilization programs.
Effect of fertilization rate on growth of container grown plants
Research has shown that increasing fertilizer rates of con-
tainer grown plants partially offsets reduction in growth caused
by smaller containers. For example, 'Formosa' azalea grown in
quart cans and given 6,000 or 9,000 lb/A/yr of a 6-6-6-1 (N,
P20s, K20, MgO) were as large as plants in gallon cans given
3,000 lb/A/yr of this fertilizer, while plants in gallon cans given
9,000 lb/A/yr of a 6-6-6-1 were as large as plants in 2 gallon
cans given 6,000 lb/A/yr of a 6-6-6-1 (31). Likewise, wax-leaf
privet grown in quart cans receiving 9,000 lb/A/yr of a 6-6-6-1
were as large as those in gallon cans given 3,000 lb/A/yr of this
fertilizer, and plants in gallon cans given 6,000 or 9,000 lb/A/yr
of 6-6-6-1 were as large as those in 2 gallon cans given 3,000
lb/A/yr of this fertilizer. Such information will be helpful to
growers when they make their decision on the level of fertiliza-
tion to use.
Research has shown that plant quality is usually correlated
with nutrient level in the leaves, and leaf analyses are good indi-
cators of the plant's need for nutrient elements. Information
from leaf analyses of plants grown in numerous experiments
viburnumm, 'Formosa' azalea, 'East Palatka' holly, wax-leaf
privet, Japanese pittosporum, lantana, and Japanese box) was
used to establish low, desirable, and high foliage content ranges
of nitrogen, phosphorus, potassium, calcium, and magnesium
given in Table 7 (32, 33, 34, 37, 38, 39, 42, 43, 44, 45). Several
factors affect ratio at which nutrient elements should be applied:
(a) influence in the medium of one element on uptake of another
such as the antagonisms of calcium, potassium, and magnesium
on each other; (b) ingredients of potting media as they affect
retention of certain elements against leaching (cation exchange
capacity) ; (c) differences in leaching rates of fertilizer ele-
ments; and (d) differences between plant species in their re-
quirements for certain elements (17, 32, 33, 34, 37, 45, 65, 66).
The "desirable ranges" given in Table 7 show that less po-
tassium than nitrogen is needed by the plants (0.40 to 1.00%
potassium versus 1.40 to 2.00% nitrogen) while phosphorus con-
tent of the foliage was always much lower (0.15 to 0.30% than
Table 7. Tentative low, desirable, and high ranges in percentage of
mineral elements in the foliage of container grown woody
Percent dry weight
Low Desirable High
Element (less than) range (more than)
Nitrogen 1.25 1.40-2.00 2.50
Phosphorus .10 .15- .30 .35
Potassium .30 .40-1.00 1.25
Calcium .50 .75-1.50 1.75
Magnesium .30 .30- .50 .60
either potassium or nitrogen. Generally, nitrogen is more subject
to leaching than potassium, and less potassium is taken up by
plants. Also less phosphorus is leached from the media and con-
siderably less is needed by the plants. Leaf analyses and experi-
mental data indicate that dolomite at the rate of 7-10 lb/cu/yd
of medium will supply container grown woody ornamental plants
with needed calcium and magnesium. In fact, in several experi-
ments amounts in the leaves show a "luxury consumption" of
magnesium (32, 37, 38, 43, 44, 45).
This information and that from experiments testing effects
of levels of one element (nitrogen) on response to levels of one
or more other elements (phosphorus and potassium) are the
basis for recommendation of approximately 4:1:2 ratio of nitro-
gen (N), to phosphoric acid (P20O), to potash (K20) for con-
tainer grown woody ornamental plants in Florida. Amounts of
needed fertilizer materials to apply are given in Tables 9, 10, 11
and in the section on fertilization programs.
To be effective, materials added to potting media at time of
mixing (dolomite, superphosphate, microelements, etc.) must be
well mixed and evenly distributed within the potting media.
Small amounts of media may be effectively mixed by hand, but
to adequately mix large volumes, properly designed "homemade"
or "readymade" equipment must be used. Available "readymade"
equipment exists which may be either leased or purchased from
Classification of Florida woody ornamental plant nurseries
based on potting media sources, and their media mixing equip-
ment, falls into three groups given in Table 8. Generally,
growers having equipment enabling them to evenly mix media
ingredients and added fertilizer amendments and those who pur-
chase their media from commercial sources have the "media
mixing" problem solved. However, nurseries lacking such equip-
ment are subject to the ills of poorly mixed media which show
up as irregular plant growth and reduction of quality resulting
from poor pH control, uneven distribution of fertilizer materials
in the media, and variable nutrient and water holding capacities.
Fertilization procedures and programs for producing con-
tainer grown woody ornamental nursery plants in Florida,
based on media source and media mixing classification of Table
8, are described herein and outlined in Tables 9, 10, and 11.
Table 8. Florida woody ornamental nurseries classified on basis of
potting media source and type of media mixing equipment.
I. Media mixed by growers.
A. Growers with equipment which will evenly mix fertilizer
materials with the potting media.
1. Potting mixture preparation. Superphosphate, dolomite,
and microelements mixed in the potting media.
2. Program A-Table 9. Soluble fertilizers applied in irri-
3. Program B-Table 9. Dry application of fertilizers to
surface of containers and/or beds.
B. Growers without equipment which will evenly mix fertilizers
with potting media.
1. Program C-Table 10. Soluble fertilizers applied in irri-
gation water and microelements applied as directed
2. Program D-Table 10. Dry fertilizers. Mixtures contain-
ing N, P2O:,, K.O and MgO in recommended ratios plus
needed microelements, copper, zinc, manganese, and iron.
3. Program E-Table 10. Dry fertilizers of B2 above with
microelements applied as directed sprays-Table 11.
II. Mixed potting media purchased from commercial sources. These
commercial media are usually well mixed and sterilized.
A. They should contain in sufficient quantities superphosphate
dolomite, and microelements-Table 9.
B. Later fertilization should be given by following either Pro-
gram A or B-Table 9.
Table 9. Guide for fertilization of container and bed grown nursery stock in Florida when superphosphate, dolomite, and micro-
elements are well mixed with the media.
Type Fertilizer Rate of application Method and time Remarks
fertilization of application
pounds per cu yd
Added to Superphosphate 21/2 4 Add during mixing. Rates are for
potting mixture superphosphate.
in preparation Dolomite1 7 -10 Add during mixing. Use dolomite to supply
calcium and magnesium
and to adjust pH to
5.5 to 6.5.
Micro (minor) elements ounces per cu yd
Copper sulfate 1 Add during soil A microelement mixture
Zinc sulfate 1 mixing and mix may be used provided
Manganese sulfate 2 thoroughly, the actual rates are
Iron chelate 1 similar.
Program A Based on use of soluble fertilizers and potting soil described above.
100 sq ft 100 gal2 acre
Surface Ammonium nitrate .46-.86 1.8-3.4 199-373 Apply ammonium Other sources of N and
application (33.5-0-0)3 nitrate and K can be used provided
potassium nitrate actual rates and ratios
Potassium nitrate .17-.35 0.7-1.4 76-152 together monthly, are similar.
Diammonium phosphate .43-.86 1.7-3.4 186-372 Once every 6 Use after 6 months and
(21.2-53.8-0)3 4 months, every 6 months thereafter.
Type Method and time
fertilization Fertilizer' Rate of application of application Remarks
Program B Based on dry application of fertilizers and potting soil described above.'
Broadcast over beds Other sources of N,
or containers placed 16-4-85'3 Monthly P, and K can be used
side by side. provided actual rates
and ratios are
rate in teaspoons for various
Surface application 1 gal 2 gal 3 gal 4 gal 5 gal Other sources of N,
to individual 16-4-8- ,: Monthly P, and K can be used
containers 1- 1/-1 -1 1'-21- 2-3'/2 provided actual rates
and ratios are
'Ground limestone may be used when calcium is needed and to raise pH.
"One hundred gallons of fertilizer solution should be applied to 400 sq ft of bed area.
:133.5-0-0 First number = % nitrogen (N); second number = % phosphorus (PO5) ; third number = % potassium (K20).
4When diammonium phosphate is used, because of the nitrogen it contains (21.2% N), reduce ammonium nitrate to .43- .83 lb per 100 sq ft, to
1.7 3.3 lb per 100 gal of water, and to 189 363 lb per acre.
5Foliage should be dry when fertilizer is applied, but water immediately after applying fertilizer.
General remarks These recommendations are designed to provide a range of 800 to 1,500 lbs of nitrogen, and 400 to 800 pounds of potash
(KO2) per acre per year. Phosphorus is applied in the soil mix and by application of diammonium phosphate every 6 months.
Rates listed are acceptable year around for south central and southern Florida. For north central and northwestern Florida, use lowest listed
rates and omit the November and January applications.
During periods of very heavy rainfall the higher rates should be used, and plants should be refertilized after heavy leaching rains -5 to 6
inches in one day or 10 to 12 inches in a week.
Table 10. Guide for fertilization of container and bed grown nursery stock in Florida when superphosphate, dolomite, and micro-
elements are not pre-mixed or are not properly mixed with the media.
Type Time of
fertilization Fertilizer' Rate of application application Remarks
Program C-Based on use of soluble fertilizers to supply needed elements.
100 sq ft 100 gal2 acre
Surface Calcium nitrate .74 1.37 2.96 5.48 326 598 Monthly These fertilizer sources
application Potassium nitrate .17- .35 .70 -1.40 76 -152 Monthly supply needed N, P, K,
to containers Diammonium phosphate .21 .43 .84 -1.72 93 186 Monthly Ca, Mg, and S.
or beds Magnesium sulfate .10- .20 .40- .80 43- 86 Monthly
Foliage Microelement sprays Table 11 gives directions for Once A commercial microelement
sprays making and applying these sprays. after mixture may be used
potting provided actual rates of
elements are similar.
Program D- Based on use of dry fertilizers to supply needed elements.
100 sq ft acre
Broadcast over Alternate a 16-4-8-23 1.0 1.8 418 782 Monthly Other sources of N, P,
beds or con- plus microelements K, and Mg may be used
tainers placed with a 12-6-8-2" 1.3- 2.4 556 -1044 provided actual rates
side by side plus microelements. and ratios are similar.
rate in teaspoons for various
Surface Alternate a 16-4-8-23 size containers Monthly Other sources of N, P,
applications plus microelements 1 gal 2 gal 3 gal 4 gal 5 gal K, and Mg may be used
to individual with a 12-6-8-2: provided actual rates
containers plus microelements. 4-i2 -/2-1 %-1 11/2-21/2 2-3%1 and ratios are similar.
Type Time of
fertilization Fertilizer Rate of Application application Remarks
Program E- Based on use of dry fertilizers and microelement sprays to supply needed elements.4
100 sq ft acre
Broadcast over Alternate a 1.0 1.8 418 782 Monthly Other sources of N, P,
beds or containers 16-4-8-21 K, and Mg may be used
placed with a 1.3- 2.4 556- 1044 provided actual rates
side by side 12-6-8-2' and ratios are similar.
rate in teaspoons for various
Surface appli- Alternate a size containers Monthly Other sources of N, P,
cation to 16-4-8-2' 1 gal 2 gal 3 gal 4 gal 5 gal K, and Mg may be used
individual with a provided actual rates
containers 12-6-8-22 14-1/ /2-1 -1 11/2-21/2 2-31/ and ratios are similar.
Foliage sprays Microelement sprays Table 11 gives directions for making Once A commercial microelement
and applying these sprays. after mixture may be used
potting provided actual rates
'Chemical contents of fertilizers are given in Table 5.
'One hundred gallons of fertilizer solution should be applied to 400 sq ft of area.
'16-4-8-2 and 12-6-8-2 N, P205, K20, and MgO respectively.
'If fertilizers contain the microelements Cu, Zn, Mn, and Fe, the microelement sprays will not be needed.
General remarks --These recommendations are designed to provide a range of 800 to 1,500 lb of nitrogen, 200 to 400 lb of phosphorus (P205),
400 to 800 lb of postassium (K20), and 150 to 300 lb of MgO per acre per year.
Rates listed are acceptable year around for south central and southern Florida. For north central and northwestern Florida, use lower range
of listed rates and omit the November and January applications.
During periods of very heavy rainfall the higher rates should be used, and plants should be refertilized after heavy leaching rains 5 to 6
inches in one day or 10 to 12 inches in a week.
I. Media mixed by growers.
A. Growers with equipment which evenly mixes fertilizer mate-
rials with components.
1. Fertilizer materials to be mixed into media Table 9.
a. Superphosphate-21/2-4 lb/cu/yd of medium. Supplies
phosphorus, calcium, sulfur, and molybdenum.
(1). If pH is adjusted to 5.5 to 6.5, this rate supplies
needed phosphorus to plants for entire growing
season, or for at least 6 months.
b. Dolomite-7-10 lb/cu/yd of medium. Calcium and mag-
nesium in dolomite plus amounts in irrigation water
supply needed calcium and magnesium for duration
plants are in containers.
(1). If pH is in desired range of 5.5 to 6.5, or in alka-
line range and calcium is needed (media contains
less than 500 lb/A), use gypsum (calcium sulfate)
at the rate of 5-7 lb/cu/yd of medium.
c. Micronutrients-Materials containing copper, zinc, man-
ganese, and iron should be mixed in the media to supply
these elements for the time plants are in containers.
(1). Copper sulfate 1 oz/cu/yd of medium.
(2). Zinc sulfate 1 oz/cu/yd of medium.
(3.) Manganese sulfate 2 oz/cu/yd of medium.
(4). Iron chelate 1 oz/cu/yd of medium.
(a). If media is in acid range (below pH 7.0) use
FeEDTA iron chelate (sodium salt of
ethylenediamine tetraacetic acid).
(b). If media pH is in the neutral to alkaline
range (pH 7.0 or above) use either the iron
chelate of sodium ferric diethylenetriamine
penetaacetate (Fe-DTPA- Sequestrene 330)
or the iron chelate of hydroxyethyl ethylene-
diamine triacetic acid (Fe-EDTA-OH-Ver-
sinol). If either of these iron chelates is
ineffective, use the iron chelate of ethylene
diamine di(o-hydroxyphenyl) acetic acid (Fe-
EDDHA Sequestrene 138).
(5). Commercial micronutrient mixtures may be used
provided the actual rates are similar.
2. Program A--Table 9. Using potting media prepared as
above and fertilizing plants with soluble fertilizers applied
as a liquid or in irrigation water.
a. Fertilization should begin immediately after containers
are placed in the nursery beds or rooted cuttings are
"lined out" in beds. Recommended fertilizer materials,
rates, and application frequency are given in Table 9-
(1). Nitrogen. Supplied monthly from ammonium
nitrate with some nitrogen (13.8% of total)
coming from potassium nitrate. Nitrogen may be
supplied from other sources provided recom-
mended rates are used (Table 9).
(2). Potassium. Supplied monthly from potassium
nitrate. Potassium may be supplied from other
sources provided recommended rates are used
(3). Phosphorus. Superphosphate mixed in potting
media will supply phosphorus for entire growing
season or at least 6 months. Only superphosphate
should be used because in addition to phosphorus
it also supplies the essential elements sulfur and
calcium (Table 6).
(a). Additional phosphorus is supplied, after the
first 6 months and every 6 months thereafter,
by applying diammonium phosphate in the
irrigation water at rates given in Table 9.
3. Program B Table 9. For application of dry fertilizers.
a. Liners planted in potting media containing superphos-
phate, dolomite, and micronutrients as previously de-
scribed. Surface application of dry fertilizer should
begin immediately after containers have been placed
in nursery beds or rooted cuttings lined out in beds.
Fertilizer formulas, rates, and application times are
given in Table 9 Program B.
(1). Use a 16-4-8 or its equivalent and apply monthly.
Rates of Table 9 are acceptable year around for
south central and southern Florida, but for north
central and northwestern Florida use one-half of
lower rates during November, December, January,
and February. An alternative procedure, which
saves two fertilizer applications per year, is to use
lower range of these rates during this period, and
omit the November and January applications.
B. Growers lacking equipment which will evenly mix fertilizer
materials (dolomite, superphosphate, micronutrients) with the
potting media and those who do not desire to mix these mate-
rials in their potting media. Procedures given in Programs C,
D, E of Tables 10 and 11 answer the problem, except for pH
control, of growers using either liquid, dry, or a combination
of the two fertilizer programs.
1. Program C -Tables 10, 11. Based on application of liquid
fertilizers to supply needed nutrient elements to bed or
container grown nursery stock.
a. Fertilization of plants after transplanting should begin
immediately after plants are placed in the field, with
liquid fertilizers (macronutrients) applied in irrigation
water, and micronutrients applied as a foliage spray.
(1). Nitrogen. Supplied monthly from calcium nitrate,
potassium nitrate, and diammonium phosphate.
(2). Potassium. Supplied monthly from potassium
(3). Phosphorus. Supplied monthly from diammonium
(4). Calcium. Supplied monthly from calcium nitrate.
(5). Magnesium. Supplied monthly from magnesium
sulfate (epsom salts).
(6). Sulfur. Supplied by magnesium sulfate.
(7). Micronutrients. Supplied from foliage sprays--
Table 11. One micronutrient spray should supply
these nutrients for one growing season.
2. Program D Table 10. Based on use of dry fertilizers to
supply needed nutrient elements to bed or container grown
a. Surface application of dry fertilizers should begin im-
mediately after containers have been placed in nursery
beds or rooted cuttings lined out in beds. Fertilizer
materials, rates, and application times are given in
Table 10 Program D.
3. Program E Tables 10, 11. Based on use of dry fertilizers
(macronutrients) and foliage micronutrient sprays to sup-
ply needed nutrient elements to bed or container grown
a. Surface application of dry fertilizers should begin im-
mediately after containers have been placed in nursery
beds or rooted cuttings lined out in beds. Fertilizer for-
mulas, rates, and application times are given in Table
10 Program E and Table 11.
II. Mixed media purchased from commercial sources.
A. These media are usually well mixed and preferably should be
sterilized (Table 8).
B. They should contain sufficient amounts of superphosphate,
dolomite, and microelements (Table 9).
C. Subsequent fertilization of plants after containers have been
placed in nursery beds should be given by following either
Program A or B, Table 9, depending on fertilization method
used by the nurseryman.
Table 11. Pounds of copper, zinc, and manganese sulfates and
hydrated lime to make 100 gallons of a copper-zinc-
manganese-lime spray mixture, and pounds of iron
chelates needed to supply iron.'
Chemical2 (lbs) Remarks
Copper sulfate 3.0 First dissolve sulfates by slowly
Zinc sulfate 3.0 dusting them into spray tank, then
Manganese sulfate 3.0 add hydrated lime and a suitable
Hydrated lime 2.3 spreader. Direct spray so as to wet
plants and surfaces of media in pots.
Iron Should be applied in a separate spray. Use iron chelate of
ethylenediamine tetraacetic acid (FeEDTA) if media pH is below
7.0. If media pH is 7.0 and above use either iron chelate of sodium
ferric diethylenetriamine pentaacetate (Fe-DTPA), or the iron che-
late of hydroxyethyl ethylenediamine triacetic acid (Fe-EDTA-OH).
FeEDTA 1.0 Dissolve in 100 gallons of water
Fe-DTPA or 1.0 Dissolve in 100 gallons of water
Fe-EDTA-OH plus spreader.
'Adapted from Table 2, Fla. Agr. Exp. Sta. Bul. 536B -Recommended
fertilizers and nutritional sprays for citrus.
2No lime is required if neutral zinc, copper, or manganese compounds are
Careful attention to total soluble salts levels is of major im-
portance. In recent years a number of Florida growers have ex-
perienced problems with high soluble salt levels in their growing
media as a result of saline media components, salty irrigation
water, and incorrect fertilization methods and rates.
When plants are subjected to soluble salt levels above their
critical level, several symptoms may occur that are similar to
those caused by other problems. Root injury may occur, and this
is expressed in above ground portions of the plant by temporary
wilting, leaf tip burn, marginal burning of young or recently
matured growth, and various chlorosis patterns which are simi-
lar to those caused by several nutritional deficiencies. However,
soluble salt injury may be less distinctive and, therefore, more
difficult to recognize. In some cases plants may grow slowly yet
appear normal in every other way. However, a check of the
media may indicate a high soluble salt level which could cause
stunting without actually causing any other noticeable injury.
When growers suspect a soluble salt problem is occurring
they can send a soil sample to a soils testing laboratory for anal-
ysis or make their own tests for soluble salts.
Soluble salts are easily estimated by mixing one part dry
media to two parts water, and reading on a Solu-Bridge at 700F.
The Solu-Bridge is calibrated to read specific conductance from
10 to 1,000 MHOS x 10-3 or 0.1 to 10 MHOS x 10-. Solu-Bridge
readings on these types of soil or potting media may be inter-
preted as shown in Table 12 for Solu-Bridge readings in MHOS
x 10-". Move the decimal two places to the left for Solu-Bridge
readings in MHOS x 10-.
In light mixes having high water holding capacity it may be
necessary to use a 1: 4 mixture of media:water. In that case the
Solu-Bridge reading should be multiplied by two in order to use
the reading provided in Table 12. Mix media and water together,
stir, and allow equilibration for at least 30 minutes before deter-
mining salt reading. After sample and water have stood the re-
quired time, the solution temperature should be taken and the
temperature dial adjusted. The common black plastic conduc-
tivity cell will require 1 to 2 ounces of extract for a good read-
ing; therefore, it will be necessary to filter a suitable volume of
the extract through cheesecloth into a clean container. Sub-
merge the cell in the solution almost to the top to insure com-
plete contact of electrodes with solution. Rotate the dial until
the electric-eye tube reaches its widest opening; then the figure
is read and recorded. The equipment necessary to perform solu-
ble salts testing is simple to operate and free from mechanical
or electrical problems. The basic equipment needed is a Solu-
Bridge, type RBD 15 (A-60), reading specific conductance from
10 to 1,000 MHOS x 10-5 or 0.1 to 10 MHOS x 10-' and having
a conductivity cell constant of 2.0 (A-124). Cost of equipment
varies from different manufacturers, but it can generally be ob-
tained for less than $150.00. Additional information on equip-
ment is available from the following sources: LeRoy E. Rogers
Company, 9 N. Highland Avenue, Clearwater, Florida; Indus-
trial Instruments, Inc., 89 Commerce Road, Cedar Grove, New
Jersey; and Soiltest, Inc., 2205 Lee Street, Evanston, Illinois.
When growers find they have excessive soluble salt levels in
their growing medium they should take corrective measures as
soon as possible to prevent further damage to their crop. Heavy
irrigation will immediately lower soluble salts to a level that can
be tolerated. Amount of water needed depends on how much the
soluble salt level is to be reduced and depth of medium to be
leached. For example, in containers 6 inches of irrigation water
Table 12. Solu-Bridge reading for 1:2 dry media to water mixture
Media MHOS x 10-5 rating Remarks
Sandy media Below 25
1:1 Peat:sand Below 33 Low Need fertilizer.
Peat or light
wt. mixes Below 50
Sandy media 25 to 50 Satisfactory for
1:1 Peat:sand 33 to 66 Low to growth in upper
Peat or light medium range.
wt. mixes 50 to 100
Sandy media 50 to 100 Desirable salt range
1:1 Peat:sand 66 to 130 Medium to no fertilizer needed,
Peat or light high but light application
wt. mixes 100 to 175 can be made.
Sandy media 100 to 150 Do not fertilize
1:1 Peat:sand 130 to 200 High to or allow media to
Peat or light very high become dry.
wt. mixes 175 to 275
Sandy media Over 150 Excessive salts may
1:1 Peat:sand Over 200 cause damage. Leach
Peat or light Excessive media.
wt. mixes Over 275
1These readings are based on medium salt tolerant plants. For salt sensi-
tive plants these scales should be decreased by approximately 25%.
leaches out approximately one-half of the salt, and 12 inches
leaches out nearly four-fifths of the salt.
Preventive practices are probably more valuable and prac-
tical than corrective measures. Periodic testing of the medium
will often detect soluble salts nearing a dangerous level, and
allows for correction of those practices causing a build-up of
soluble salts in the medium.
Methods of watering and amount of moisture in the medium
probably affect soluble salt levels more than any other factor.
Since soluble salts are measured on a conductivity basis, an in-
crease or decrease in either total salt or water content will sig-
nificantly affect the reading. Where salinity is a problem, crops
should not be grown on the "dry side" because medium to high
moisture in the medium reduces salt levels. For example, a
medium containing 500 ppm salt at 50%o moisture will contain
approximately 1,000 ppm salt at 25% moisture. Therefore, in
container nursery production the grower should maintain high
moisture levels in the medium to prevent wide fluctuations in
soluble salt content. The method of watering and maintenance
of a high moisture level in the medium are also important. If
insufficient water is applied each time containers are watered,
salts may build up because no leaching of the medium is oc-
Other factors affecting total soluble salt levels besides water-
ing frequency includes salinity of water, original growing me-
dium, and the fertilization program. Irrigation water containing
large amounts of soluble salts should not be used for watering
foliage plants. Waters with salt levels as high as 1,200 ppm can
be used, except on plants highly susceptible to soluble salts in-
jury such as varieties of Southern Indian azaleas (105), pro-
vided sufficient leaching occurs each time the plants are watered.
Irrigation waters with 600 ppm soluble salts or less are consid-
ered best for container nursery stock production.
Table 13 gives basic information on water quality and ap-
proximate permissible limits of various constituents.
Numerous cases have been reported where peat moss and
other potting mix components contained excessive levels of solu-
ble salts. In these cases the corrective action to be taken is to
thoroughly leach, or to discard a particular lot in favor of
another. New lots of peat moss or other materials may have high
soluble salt levels due to several causes, of which the following
are common: (a) mining from salt marshes; (b) mining from
areas recently covered by sea water; (c) transportation on decks
of ships where they were subject to salt spray; and (d) mining
from bogs where drainage water containing salts can be accu-
mulated from higher areas.
Table 13. Classes of irrigation water and permissible limits of
Electrical Total dis-
conductance solved solids Sodium
Class of E.C. x 10-" (salts) percent of
water at 25C 2 ppm total solids
1. Excellent Less than 25 175 20
2. Good 25 to 75 175 to 525 20 to 40
3. Permissible 75 to 200 525 to 1400 40 to 60
4. Doubtful 200 to 300 1400 to 2100 60 to 80
5. Unsuitable More than 300 2100 80
1Source: L. V. Wilcox. 1948. The quality of water for irrigation use.
USDA Tech. Bul. 962. p. 27.
2In order to convert Solu-Bridge Model RD-15 reading on well water or
other irrigation water, multiply the reading of the water in MHOs x 10-5
by 7. This will approximate the ppm total soluble salts in the water.
Another primary source of soluble salts is an incorrect fer-
tilizer program. Sources of various essential fertilizer elements
are almost always salts such as potassium chloride, sodium ni-
trate, and ammonium nitrate (Table 6). When such salts are
added to the growing medium the osmotic (salt) concentration
of the media solution increases. If this concentration exceeds the
osmotic concentration of plant cells of absorbing root hairs,
water will be withdrawn from the roots. When water moves out
of plant cells into the media solution, it causes partial or com-
plete dessication of roots (soluble salt injury). Therefore, the
fertilizer program must supply the right amounts of fertilizer
in the proper time period in a manner to prevent application of
too much at one time.
As previously stated, level of soluble salts present in the
medium depends on moisture holding capacity of the medium,
and also on cation exchange capacity of that medium. The higher
the cation exchange capacity of a particular medium, the more
fertilizer that can be applied without radically affecting soluble
salt levels. However, this has led to a false assumption by many
growers that any media with lots of peat present will have few
if any soluble salt problems. Such a medium can contain more
salts than a medium without peat present, but it will also leach
less rapidly and allow a possible build-up of excess soluble salts
due to higher moisture and cation exchange capacities.
IRRIGATION AND SOIL OR MEDIA MOISTURE
Although most water removed from the soil or media by
plants is lost to the atmosphere through transpiration, the small
portion utilized in photosynthesis is vital in production of car-
bohydrates necessary for growth. Therefore, application of the
right amount of good quality water to container grown nursery
stock at the optimum time is an important factor in production
of quality plants.
In Florida, container grown nursery plants use large amounts
of water continuously, but rate of use depends on plant species,
size, temperature, and atmospheric conditions. The enormous
requirements of plants for water is shown by the fact that 300
to 500 pounds of water are necessary to produce one pound of
dry organic matter. Although water serves the plant as a sol-
vent, transporting agent, and the main constituent of plant cells,
over 99% of the water absorbed is transpired to the atmosphere
The water requirements of container grown nursery plants
vary because of age, succulence of growth, and species of plant.
Young plants with little top growth require less water because
they lose less water by transpiration than larger plants in a
similar size container. Plants growing rapidly with extensive
succulent growth usually wilt sooner, because more of the tissue
is composed of water. Plant species is also very important, as
those with large thin leaves absorb and transpire water more
rapidly than those with small thick leaves, as exhibited by broad-
leaved evergreens and conifers.
On the basis of differential water requirements of container
grown ornamentals, plants should be grouped according to con-
tainer size and type, and similar moisture requirements. Growth
rate should be considered, as a rapidly growing plant will soon
develop a large top, and if in a block with slower growing species,
will determine the watering frequency. The increased frequency
may not injure other plants present, but will necessitate in-
Quality of irrigation water is very important in container
nursery plant production because of undersirable chemicals
found in some waters. When a new well or growing operation is
being planned, water sources should be checked for total dis-
solved constituents. For the water to be good, soluble salt levels
should be below 600 ppm, and generally water above 1,200 ppm
should not be used (see section on soluble salts). Specific chem-
icals found in some water that may cause plant injury include
chlorine, fluorine, and boron. Chemicals that leave undesirable
foliar residues include iron, calcium, and magnesium. Drainage
ponds and pools are not generally desirable sources of irrigation
water because of the possibility of disease organisms and weed
seed being distributed over the plants, because of algae and
other organisms developing which may clog the irrigation sys-
SOIL OR MEDIA FACTORS
The importance of adequate water holding capacity and
proper aeration and drainage of container mixes cannot be
stressed too strongly.
Water holding capacity, the ability of a soil or media to hold
water against the pull of gravity, is important because it deter-
mines irrigation interval and influences fertility control. Of the
total water held in a particular potting mixture, only part of it
is available to the plant, and is that portion between soil or
media capacity and permanent wilting point.
The most meaningful measurement of water present in a
particular potting mixture is percent by volume of moisture
(water) held after irrigation and all gravity water has drained
(63). Maximum soil water content in percent dry weight is ob-
tained by weighing total medium with gravitational water re-
moved, oven drying at 105C, reweighing and dividing the dif-
ference by dry weight. Fifteen atmosphere percentage can be
determined on a pressure membrane apparatus. Difference be-
tween maximum water content and the fifteen atmosphere per-
centage is considered available water. These can be converted to
volume basis by multiplying their percent dry weight by bulk
density. Container media used for growing woody ornamentals
should have at least 5-10% available water holding capacity by
volume and 40-50%c maximum water by volume. Table 2 of the
growing media section provides a guide to water holding capa-
cities of some representative media types.
Proper drainage and aeration of container mixtures is as
important as water holding capacity. Media aeration directly in-
fluences plant growth by its effect on soil oxygen, which controls
to a large extent the uptake of nutrients and water. The major
factor affecting drainage and aeration is type of potting mixture,
but the surface beneath containers as well as drainage holes and
other factors near these drainage holes are also important (26).
Drainable pore space should be approximately 10Q; to pro-
vide adequate aeration and drainage. The suggested potting mix-
tures meet this requirement. A simple method of checking drain-
age is to add water to the top of a container to a depth of 1 inch.
If this water moves into the potting mixture within 2 minutes
the percentage of pore space is adequate. The more time (be-
yond 2 minutes) required for the water to enter the media the
less satisfactory the potting mixture. Mixtures requiring 5 min-
utes or more to drain are completely unsatisfactory for container
production and should be discarded.
The surface beneath containers influences drainage, and this,
in turn, affects depth of media that remains saturated in the
bottom of the container. Placement of containers on soil provides
best drainage followed by sawdust. However, most nurserymen
utilize black plastic beneath containers for weed control, and
this practice can result in poor drainage within containers when
water is trapped around the base of the container. This may be
minimized by grading beds at least 4 inches higher in middle of
bed than at edges and compacting the bed prior to laying the
plastic and setting cans.
Tests with unpainted and oil painted metal containers have
shown that drainage can be blocked by formation of a rust-soil
crust over drainage holes. Another important factor in im-
proving drainage is selection of containers with large side-drain-
age holes. Placing coarse gravel or other material in the bottom
of containers to improve drainage was ineffective, and plants in
containers placed on a substratum of sawdust to improve drain-
age were no better than plants grown without this treatment
Experience and good judgement are essential in determining
how much and when to irrigate under any particular set of con-
ditions. Generally, plants should be watered prior to wilting,
and the medium should not be allowed to dry out between water-
ings. The amount of water required by container grown plants,
and frequency of irrigation depends on water holding capacity
of the potting mixture, amount of water already present in the
mixture, size of plant and container, species of plant, tempera-
ture, humidity, and wind speed.
Water control is important because its application costs
money; too little will retard growth and reduce quality, while
too much will leach fertilizers and reduce aeration. Research
(43, 44) indicates that container grown plants in Florida under
full sunlight require daily watering when mature except during
cloudy and/or cool weather when watering every two days is
usually adequate. When media mixtures have a lower water
holding capacity than those listed in the section on growing
media, more frequent irrigation will be necessary. When 35 to
50% shade is supplied by either polypropylene or lath, plants
usually require watering every 2 days, and during cloudy
and/or cool weather this may be extended to 3 days.
The amount of water to apply at any irrigation depends on
the amount required within the container, the amount deflected
by the plant canopy which is lost between containers when over-
head sprinklers are used, and the portion evaporated during ap-
plication. Generally, small plants that do not cover the container
receive most of the water applied with sprinklers, while up to
50' may be deflected by the canopy of large plants, requiring
application of up to 2 inches to place 1 inch in the containers.
Normally the amount of water at each watering for suggested
potting mixtures varies between i, to 1 inch, depending on con-
Key components of any irrigation system are the well, pump,
and proper size main and lateral lines. Frequently these com-
ponents are undersized for the area to be watered, and serious
inefficiencies occur. Since proper engineering of a watering sys-
tem is necessary, that subject is not covered in this discussion.
However, information is provided on this subject in a number
of easy-to-understand, low cost bulletins (59, 60, 61).
Overhead sprinkling is the most commonly used method of
irrigation in container nurseries. Other irrigation methods in-
clude individual containers by tube trickle and sub-irrigation.
Use of tube trickle systems is increasing. General information
on each of these systems follows, with mention of some of the
major advantages and disadvantages associated with each
This method of application is low in initial system costs as
well as upkeep costs, and it does an acceptable job if properly
engineered. A major drawback is uneven distribution of the
water, which is more serious when the system is also used for
application of fertilizers, herbicides and pesticides. Another
drawback is that it promotes the development and spread of
Efficiency of overhead sprinklers is influenced by type of
head, spacing, and wind velocity. Fixed spray heads are best for
smaller areas where they are protected from wind, and they are
most satisfactory for smaller containers.
The most common type of sprinkler head found in nurseries
is the rotating impact type, which supplies water with consider-
able force. This force is desirable for field-grown container nur-
sery stock to obtain wide coverage, but the plant's top may de-
flect some of the water, causing it to fall outside the container
rather than enter media in the containers. These sprinkler heads
are best for container sizes of 1 to 5 gallons, and provide satis-
factory coverage in calm to 5 MPH wind conditions.
Whirling rotating sprinklers of various design provide ex-
cellent coverage, but do not penetrate when plants have a canopy
over the media surface because water droplet size is small. This
type sprinkler operates best in protected locations such as shade
INDIVIDUAL CONTAINER IRRIGATION
Recent advances in design of small low-cost plastic tubing
provide an excellent method of watering individual containers.
This system is expensive to install, but will provide irrigation to
individual containers without wetting the foliage under all wind
conditions. These systems seem best adapted to larger containers
in Florida (5 gallons and larger) when the inside diameter of
tubing is 1/8" or larger. Smaller tubing, especially that with an
inside diameter of 0.045 inch, frequently becomes clogged be-
cause of the high calcium and magnesium levels of most Florida
waters and from growth of algae and/or bacteria within the
tubes. When small diameter tubing is used, water treatment is
desirable. Tube-type (trickle) irrigation can also be used for
injection fertilization and application of systemic insecticides
This method is frequently used for field grown crops where
hardpans exist near the soil surface, but only a few nurseries use
subirrigation for containers. Although this method of irrigation
provides desired amounts of water, construction of beds to hold
water is too expensive for most growers. Another disadvantage
of sub-irrigation is the continuous sheet of water which provides
a carrier for transmission of root rot organisms. Continuous
capillary watering may also lead to salt build up on surface of
the media under a roof. This would not occur where plants are
in the open exposed to rainfall.
OTHER IRRIGATION SYSTEM USES
When overhead sprinkling, or tube-type irrigation systems
are properly designed or engineered they can be used for appli-
cation of fertilizers and systemic fungicides and insecticides. In
addition, overhead sprinklers may be used to apply herbicides
when coverage does not vary more than about 50 / Yet, other
methods of applying heribicides appear more desirable because
more uniform application of herbicides is needed than most irri-
gation systems will provide.
When applying pesticides, always calculate the total area cov-
ered by the sprinklers and apply the exact amount of chemical
listed on the label or recommended for that crop. After applica-
tion, flush the irrigation lines and wash off the plants if re-
quired for the specific chemical used.
Cost of controlling weeds is a major factor in container plant
production. It has been representing up to 30 % of the total cost
of production in many nurseries (80). However, this figure is
considerably less in nurseries where modern weed control tech-
niques are used in place of hand labor. Factors of importance in
any weed control program include use of proper herbicides at
the proper time and at the proper rate.
WEED CONTROL IN THE CONTAINER NURSERY AREA
Three general methods, other than hand pulling and mowing,
are used to control weeds between containers, in aisles, and
around the edges of container beds. These include the use of
herbicides, black plastic ground cover, and mulch materials such
as sawdust or shavings.
Casoron (dichlobenil), Eptam (EPTC), and methyl bromide
(Table 14) may provide good control of perennial weeds such as
nutsedge (nut-grass) and bermudagrass between containers.
Table 14. Herbicides for use beneath container grown nursery
Herbicide ai/acrel Remarks
Dichlobenil 10 lbs Apply to surface with a
(Casoron) cyclone spreader-rototill
2 ways to a depth of 6 inches.
EPTC 6 lbs Application same as above.
(Eptam) Least desirable because of
short term control.
Methyl 435 to Apply under a plastic cover
bromide 650 lbs and leave in place for 48 hours.
'Pounds of actual ingredient per acre.
However, the area should be treated before containers are placed
on the container bed, and then the bed should be covered with
black plastic. If a ground cover is not used, effectiveness of these
herbicides will be lost through vaporization and leaching. Black
plastic (polyethylene) alone will prevent growth of most weeds.
Nursery plant roots growing through black plastic will not be
affected by Eptam or methyl bromide in the soil below, but they
will be killed by Casoron. However, Casoron will not be taken
up by the plant, so only root pruning will occur, with little or no
plant injury. Casoron (16) has been one of the best herbicides
for control of nutsedge between containers. If Casoron is roto-
tilled into the soil, the areas will not be suitable for production
of field-grown plants for a period of up to 2 years. Eptam will
provide only short term weed control, and for this reason feasi-
bility of its use is questionable.
Table 15. Herbicides for use in aisles and around edges of nursery
Herbicide' ai/acre' Remarks
Paraquat 1/ lb Kills weeds on contact, does not pro-
vide residual killing action. Use as a
directed spray, or use a shield to pro-
tect plants. Herbicide contact will
kill green leaves of stems.
Glyphosate 2 lbs Kills weeds after being translocated to
(Roundup) roots. Weeds should not sprout back
from roots. Use as a directed spray.
A shield should provide added plant
Oryzalin 3 to 4 lbs Similar to trifluralin, but it does
(Surflan) not have to be soil incorporated.
Diuron 4 to 5 lbs Use according to container label
Simazine 4 to 5 lbs Use according to container label
'To kill existing weeds and prevent weed seed which may be present from
germinating, both a contact herbicide and a preemergence herbicide may
-Pounds of actual ingredient per acre.
Herbicides to consider for weed control in aisles and around
the edges of container beds (Table 15) include Paraquat and
Roundup (glyphosate) for postemergence control and Surflan
(oryzalin), Princep (simazine), and Karmex (diuron) for pre-
emergence control. If weeds are already growing, it could be
beneficial to use a postemergence herbicide to kill existing weeds
and then follow this with a preemergence herbicide to control
weeds which otherwise would germinate during the next few
Use of black plastic beneath containers has become almost
a necessity for reducing weed problems between containers.
However, black plastic alone may be insufficient if nutsedge is
present in the nursery, and the area under it is not treated as
previously suggested. In such cases nutsedge may grow through
the plastic and can only be removed by hand pulling.
Before black plastic is laid down in the nursery, the area
should be graded and firmed so the center of the bed is raised
at least 4 inches above the edges. This grading will prevent
puddling of water around containers and aid in rapid movement
of water from the container bed. Loss of occasional plants may
result from water standing in low places on the plastic if the
bed is not graded properly for good drainage.
Materials such as sawdust or shavings are useful in reducing
weed problems in nurseries. Mulches can be placed on the soil
and will inhibit weed seed germination (80). In time, however,
these mulches will break down and lose their effectiveness for
weed control. They will also leave a dark humus material which
may be slippery to walk on. Therefore, it may be necessary to
replace the mulch every 6 to 12 months.
WEED CONTROL IN CONTAINERS
Controlling weeds in containers has been the most trouble-
some problem facing container growers. Cost of hand weeding
has been found to exceed $3,600 per acre per year where no
herbicides were used in containers. Methods that have had some
success in reducing weed growth in containers include mulches
of bark, sawdust, or shavings; fiberglass pads; and media sterili-
zation. Use of herbicides has proven to be a safe and more eco-
nomically feasible method, but plant injury problems may be
much greater with container grown plants than under field con-
ditions (23, 74, 80).
Weed problems can be reduced considerably by sterilizing
the potting media with methyl bromide, steam, or media pas-
teurizer-mixing equipment which uses a gas flame as described
under "Mechanization". The potting media should be treated
with methyl bromide at the rate of 11/2 pounds per cubic yard
of media, steam sterilized at a minimum of 160F for 30 min-
utes, or mixed in the pasteurizer-mixing equipment. Use of both
sterilized media and herbicides for controlling weeds around and
beneath containers will greatly reduce weed problems in the
growing area. As a result, only a minimum of hand pulling
should be needed to remove the weeds that do grow.
Materials such as fiberglass pads, sawdust, bark chips, or
shavings have been useful in reducing weed problems in con-
tainers (80). These mulches prevent sunlight from reaching
germinating weed seedlings. Generally, about /2 to 1 inch of
sawdust, bark chips, or shavings is placed on the media surface.
This practice can be successful, but heavy rains may at times
cause much of the woody material to float away. The weed re-
tarding ability of the remaining material is reduced since light
penetration is increased.
Fiberglass pads are expensive and time consuming to install.
They last for duration of the container crop; however, weed seed
may germinate around inside edges of the containers, and ef-
fectiveness of the pads is reduced as the weeds grow and push
the pads out of place.
A number of herbicides have been tested for control of weeds
growing in containers with ornamentals (23, 74, 103, 104, 107).
Even though some of these herbicides tested are excellent, none
have been registered by EPA for the specific uses and applica-
tion conditions needed for use on container grown plants in
Three herbicides that have provided good weed control in
container grown woody plants are Treflan (trifluralin), Lasso
(alachlor), and Ronstar (oxadiazon). Experimental results
show that Treflan 5% G at 5 pounds, Lasso II 15% G at 4 to 8
pounds, and Ronstar 2% G at 3 to 4 pounds active ingredient
per acre (lb ai/A) have given good weed control with little or
no injury to several species of woody ornamentals (80, 103,
104). These herbicides have each been evaluated in Florida at
rates two to four times as great as these to determine toxicity
to plants, and they have been reapplied at 2-month intervals at
these rates for one year on 10 species representing a wide range
of woody ornamental types (103). The herbicides were applied
broadcast over the top of the container plants with a cyclone
type herbicide applicator, and 1/ to 1 inch of water was applied
by sprinkler irrigation within a few hours after herbicide ap-
plication. Irrigation is needed to wash the herbicide off plant
leaves and also to incorporate and activate the herbicide. Gran-
ular herbicides should not be applied to nursery plants when
leaves are wet. Also, other pesticides should not be applied
within 1 week before or after herbicides to reduce possibilities
of injury. Lasso appears to be the most phytotoxic and least ef-
fective of these herbicides; however, there appears to be an
adequate margin for use on most types of well rooted woody
ornamentals. Emulsifiable concentrate formulations of Treflan
and Lasso have been used with considerable success when in-
jected and applied through irrigation systems. However, results
should be better from the broadcast application of granular for-
mulations because greater precision is possible in getting the
proper rates applied, and most irrigation systems will not dis-
tribute herbicides as uniformily as needed for best results.
Treflan has a lengthy list of woody ornamentals in its EPA
approved label: however, the label does not specify use on con-
tainers, the rates, or reapplication intervals needed for good re-
sults in container nurseries. Ronstar should be commercially
available and have an EPA label covering the above conditions
for use in the near future. Lasso has been used widely in nur-
series with good results, but prospects for an EPA label for this
use are very questionable because of reluctance by the manu-
facturer to apply for such a label. Without the proper label, these
herbicides cannot be recommended even though their perform-
ance has been very good.
LIGHT AND TEMPERATURE RELATIONSHIPS
EFFECTS OF LIGHT
Light, in the presence of oxygen, carbon dioxide, and the
chlorophyll of living plants, triggers internal mechanisms that
synthesize sugars. Plants are unique in this ability to produce
their own food supply-- carbohydrates. Carbohydrates in the
form of starch, hemicellulose, and cellulose make up the major
structural portions of plants. Carbohydrates in the form of solu-
ble sugars are the materials necessary for respiration, which
provides energy for plant growth and development. Carbohy-
drates also provide the basis for development of fats and pro-
teins, which are major components of living cells. Within given
ranges for each plant, the amount of light the plant receives de-
termines the amount of carbohydrates synthesized and thus de-
termines growth and quality potential for plants.
Effectiveness of light in production of carbohydrates is
closely correlated with nutrition generally, but especially nitro-
gen. Within limits, the higher the light intensity, all other factors
being favorable, the greater the amount of nitrogen or fertilizer
plants can use efficiently and profitably. A majority of the woody
plants that are grown for landscape purposes in Florida grow
well or best under conditions of full sunlight. Such plants can
efficiently use relatively high amounts of fertilizer (see section
on fertilization). However, when grown under increasing
amounts of shade, they become leggy (having long internodes),
darker green in color, and more succulent. Under heavy shade
they lose structural strength and fall over.
Some plants such as azaleas and common camellia usually do
not tolerate full sunlight conditions well. In full sunlight growth
may be retarded, their stems and leaves may become thick and
brittle, and they may become pale green and of generally poor
quality. Most of these plants will do best with 20% to 40% of
the light excluded. For best growth and quality, they should be
grown under the highest light intensity possible that will allow
for quality development. Where heavier shade is being used,
these plants should receive less fertilizer than those in higher
Plants exposed to maximum allowable sunlight prior to
freezing temperatures will withstand lower temperatures with
less injury than those under less light. This is a result of higher
carbohydrate levels (particularly soluble sugars) acquired in
the high light intensities. Higher amounts of nitrogen that can
be effectively used by plants under conditions of high light inten-
sities also aid in making plants more cold tolerant.
A few species such as viburnum, Japanese pittosporum, com-
mon camellia, Chinese hibiscus, and cultivars of the Southern
Indian and Kurume azaleas will produce higher quality when
grown under light shade compared with full sunlight (14, 44).
Part of this shade effect can be offset by higher fertilization.
Generally, the increase in quality from shading barely compen-
sates for the high cost of providing shade. Such judgements on
the economic value of establishing shade areas for growing
woody ornamental plants will have to be made by individual
nurserymen from their experience. Harmful effects of high light
shown by some plants can be partially offset with high fertilizer
applications. High light intensity prior to subfreezing tempera-
tures will help make a plant more resistant to freeze injury.
EFFECTS OF TEMPERATURE
Temperature variations, either up or down, produce changes
in plant response to the environment. Temperature, by con-
trolling plant respiration rate, affects the rate and quantity of
water and nutrient absorption and translocation; rate and
amount of photosynthesis and transpiration; availability of nu-
trients in the soil mass due to microorganism activity; plant
dormancy; time and quality of flowering; and other plant re-
sponses. Cold temperatures, below those that can be tolerated by
a plant, will produce varying degrees of freeze injury. Most or-
namental plants in Florida grow best at a temperature range be-
tween 700 and 950F. Temperatures above or below that range
require some adjustments by nurserymen to compensate for
variations in plant needs and responses.
HIGH TEMPERATURE PROBLEMS
High temperatures can result in water loss from plants by
transpiration at a faster rate than root systems can absorb
water to replace the loss; thus wilting occurs even though there
might be adequate moisture in the soil. Wilted plants have re-
duced capacity for photosynthesis, which manufactures the dry
weight mass of plants. This reduction occurs at a time when
respiration, which utilizes photosynthetic materials, is at its
peak. Under such conditions there is a loss of plant dry weight.
Additionally, very high temperatures reduce permeability of cell
membranes within plants, causing reduction in translocation of
water, nutrients, and sugar from one part of the plant to
another. All of these things are detrimental to plant growth.
Temperatures above 950F are not uncommon in Florida,
particularly at ground level when the soil absorbs and reflects
light and heat.
Media temperatures, particularly of dark media common to
ornamental plant production, are often several degrees higher
than air temperatures during late spring, summer, and early
fall months. Root systems of plants growing in containers are
subject to greater variations in temperature than those grown
in the field because there is more exposure of the soil volume in
which they grow to air temperatures, and containers contribute
to a greater fluctuation in absorption and loss of heat. As a re-
sult, temperatures of media in contact with container walls ex-
posed to high light intensities may rise above lethal tempera-
tures (1040 to 1100F), killing peripheral roots and causing a
corresponding decrease in top growth (46, 94).
Reflected heat from bare soils can also cause increases of
temperatures around bases of stems and lower leaves on sunny,
hot days when there is little air movement.
Reduction in growth caused by high temperatures can be
prevented by providing an insulating mulch on soil surfaces in
and under containers, by providing partial shade during the
hottest seasons, or by lightly watering plants with an overhead
irrigation system intermittently during hottest parts of each
LOW TEMPERATURE INJURY
Generally there are two types of injury to plants due to ex-
posure to low temperatures. They are chilling injury and freeze
damage. As temperatures drop below optimum levels, all living
processes of plants slow down. Respiration rate decreases, ab-
sorption of water and nutrients is reduced, and cell membrane
permeability is reduced so that translocation within plants is
Chilling injury is damage or death of plants resulting from
temperatures that are relatively low but still above the freezing
point of plant tissue. Some tropical and semi-tropical species are
injured at temperatures from 350 to 420F and killed at tempera-
tures from 320 to 350F. The exact cause of chilling injury is
unknown, but it is credited to disruption of the metabolic activi-
ties of the plant. Except for using techniques to maintain higher
temperatures immediately around species subject to chilling
damage, there is nothing that can be done to protect plants from
this type injury.
Plants lose heat to the atmosphere by conduction, convection,
or radiation. Conduction is the flow of heat into or out of plants
by direct contact with other objects or air near plants. This type
of loss is relatively unimportant to plants, since they do not con-
duct heat readily. Convection is a process by which heat is car-
ried away by moving air which is cooler than the plants. Loss
of heat and resultant injury due to convection is important.
Radiation is the loss of heat from plants by heat waves passing
directly into the atmosphere.
Plant tissue can freeze due to frost formation even though
air temperatures are above the freezing point. Frost usually oc-
curs when air temperatures are between 33' to 380F, the air is
still, and the sky completely clear. Under such conditions plant
surfaces radiate heat into the air, and if there is not a cloud
cover or some other covering to bounce the heat waves back to
the plant, the radiation loss causes the plant surfaces to become
colder than the surrounding air. Plant temperature then actually
drops below the freezing point, and injury occurs.
Frost injury can be prevented by stirring up the air around
plants by such things as wind machines to constantly bring
warmer air into contact with plant surfaces that are radiating
heat, thus preventing the plants from becoming colder than the
air surrounding them. Any type of cover that will reflect the
heat waves being radiated by plants back to leaf surfaces will
also prevent formation of frost. This will often explain why
plants growing under eaves of houses or canopies of trees will
survive frost damage when plants growing in open areas nearby
are killed or severely injured.
Freeze injury in plants results from mechanical puncturing
of cell components due to expanding ice crystals formed within
or between cells or from desiccation or drying-out of cells from
Most plant tissue does not freeze at 32F, the freezing point
of pure water, because of the salts, sugars, and proteins dis-
solved in the plant sap. For most tissue to freeze, temperatures
must reach 28 F or lower and remain at that point for several
hours, depending on species. The amount of injury resulting
from freezing temperatures depends on the plant species, the
rapidity of temperature drop, the ultimate low to which the tem-
perature reaches, the length of time temperature stays below
freezing point of the plant and general condition of the plant at
time of freezing. Perhaps the three most important factors af-
fecting degree of damage resulting from freezing temperatures
are the general health of the plant, the low temperature reached,
and the duration of time the plant is subjected to such sub-
The first consideration in producing cold tolerance in plants
is to adjust cultural factors to condition plants for low tempera-
tures. Plants having relatively high amounts of soluble salts,
sugars, and proteins at time of low temperatures will withstand
lower temperatures for longer periods of time without serious
injury than plants in a converse condition. To increase cold
tolerance, plants should receive as high a light intensity as they
will tolerate as long before anticipated cold weather as possible,
and should receive ample fertilization throughout the year to
maintain optimum growth. The high light intensity will allow
for maximum synthesis of sugars and proteins if, and only if,
the plant is maintained under an excellent nutritional program.
Recommendations in the past from many sources have been
to stop fertilization of ornamental plants in the fall and through-
out winter months or to use low nitrogen-high potassium ferti-
lizers during this time to "harden" plants for low temperatures.
Part of the argument for such recommendations is that this
technique prevents vegetative growth of plants during winter
months and the production of new growth which is winter killed.
Considerable research by Dickey et al. (42, 43) and Joiner and
Conover (19, 67) plus work that has been done in northern
states disprove these recommendations. Adequate fertilization
throughout fall and winter months actually allows plants to
withstand lower temperatures longer and to recover from dam-
age much faster in the spring than plants inadequately ferti-
lized. Some work with citrus and other plants in Florida indi-
cates that relatively high nitrogen supply, even to the point of
luxury consumption, can be beneficial in increasing cold resis-
tance. Proper ratio or balance of fertilizer elements is as im-
portant as quantity of fertilizer supplied in inducing cold toler-
ance (See section on fertilizer recommendations). A plant de-
ficient in any element has less ability to withstand injury from
freezing temperatures than a plant healthy in all respects.
Slightly wilted plants will generally tolerate lower tempera-
tures without injury than will those completely turgid. On the
other hand, a well moistened soil will absorb more heat during a
bright day than a dry one, and this extra heat given off at night
often is enough to protect many plants from injury when tem-
peratures are near the critical point. So many other aspects of
growth are adversely affected by wilting that allowing plants to
wilt as a cold protective measure is not recommended.
Plants kept free of pests are usually in a better condition to
withstand subfreezing temperatures simply because they are in
a healthier condition than those injured by insect or disease
pests. Certain insect sprays, especially oil emulsions, make plants
more susceptible to cold injury if used when the temperature is
below about 400F and applied more often than about every 6
weeks during winter months.
PROTECTION FROM COLD INJURY
Site selection for nursery production areas is vitally impor-
tant in preventing or reducing cold damage. Where possible,
south-facing slopes should be chosen, and relatively high land
with ample air drainage is desirable. Cold air, being heavier than
warm air, will settle into low areas, especially during times of
calm. Even with the best choice of land, artificial methods of in-
creasing temperatures will be necessary to protect cold-sensitive
Wind machines offer some protection only during times when
the wind is less than 5 miles per hour, there is an inversion layer
of warm air over the low, cold layer, and the temperature is near
the critical point. Effectiveness of wind machines decrease
rapidly as temperatures drop below the critical point. Heaters
plus wind machines offer added protection.
Heaters of various types are on the market with different
claims of excellence. The most satisfactory seem to be those
producing both radiant heat (about 65%c to 75c ) and convective
heat (about 25%; to 3552). Radiant heaters are available that
are fueled with LP gas, diesel, and other fuels, and are most
effective when heated red hot. The radiant heat waves from the
hot metal pass through the air and warm surfaces of plants and
other objects without significantly raising air temperatures,
while convective heat raises the air temperature. Closeness of
spacing depends on crop and expected low temperature, but
heaters usually are placed not less than 30 to 50 feet apart.
Effectiveness of radiant heaters depends on gross heat produc-
tion, wind speed, and density in spacing. As with other systems,
effectiveness decreases with decreasing temperatures. Davis and
Gerber (21) give an important point for nurserymen to remem-
ber in using radiant heaters.
Radiant heat travels by "line of sight" and obeys the law of
inverse squares. That is, areas two and three units distance,
respectively, from a heat source would receive 1/ and 1/9 as
much radiant heat as an area one unit distance from the heat
Some plant species will be burned if they are within a few
feet of a heater. Also, radiant heaters should not be used under
plastic cloth as they will burn holes in the plastic. When con-
vective type heaters are used in the open air, temperatures are
significantly raised only when wind speed is not above 2 to 3
miles per hour.
Sprinkler systems have proved successful in some instances
in protecting plants against freeze injury. To be effective,
sprinklers must be turned on prior to freezing temperatures and
must remain on until all ice has melted from plants. They must
also apply from 1/3 to 1/ inch of water per hour during time of
subfreezing temperatures. The weight of ice formed during pro-
longed freezing weather may break and otherwise injure many
plants, particularly large ones. Ice will usually build up from the
base of smaller plants and cause less damage to them.
Research has established that otherwise hardy plants may
be killed by severe cold when grown in containers, because the
cold kills their root systems, though their tops suffer little if any
injury. These plants may suffer relatively little injury at the
same temperature when they are growing in the field. This type
of freeze injury has occurred a few times in recent years in the
lower south which includes north and northwestern Florida. The
freeze in December 1962 is an example. Methods of reducing
this type of freeze injury are: (a) "jamming" the cans close
together, which provides protection to all cans except the two
outer rows; (b) erecting a mechanical windbreak barrier, which
helps protect the containers from rapid cooling by the wind; and
(c) placing cans in piles (sides parallel to the ground) and
using, where possible, some type of insulation material over
these piles to reduce the amount of cold injury. The windbreak
barrier should be at least 4 feet high, and could be made of
material such as plywood. Experimentally, polystyrene liners for
the cans have reduced this type of injury and deserve further
Considerable research is underway in many states on the use
of chemicals to induce dormancy and otherwise cause plants to
be more tolerant of subfreezing temperatures, but none yet have
proved to be commercially successful.
Several authors recommended shading plants from sunlight
immediately after they have frozen to reduce the rate of thaw,
claiming that this helps prevent damage from low temperatures.
There is insufficient research data to prove the value of this pro-
cedure in reducing cold damage, and considerable evidence indi-
cates that this technique does not help.
Cost of production and business analysis studies made in the
nursery industry in Florida and elsewhere have shown that the
most important factor contributing to the cost of producing nur-
sery plants is that of labor. Traditionally, many production oper-
ations in the nursery such as mixing potting media, potting
plants, fertilizing, spraying, weed control, and pruning have
been done by hand labor. The "stoop" and "hand" labor, used
extensively by the nursery industry in the past, is becoming in-
creasingly difficult to obtain and to keep on the job. Labor costs
have risen sharply since World War II, and labor specialists tell
us that labor costs will continue upward as minimum hourly
wage continues to increase while labor supply decreases. The
nurseryman, in order to make a reasonable profit on his time
and investment, or even to stay in business, must do something
to reduce the labor "cost-price-squeeze" in which he is caught.
A management decision frequently confronting nurserymen
is whether or not to invest in labor-saving and time-saving
mechanical equipment. If the decision is yes, then decisions as
to type of equipment and amount of money that can be invested
follow. Some equipment designed for nursery operations is al-
ready on the market; some equipment developed for other pur-
poses may be adapted for use by the nurseryman; or he may
develop his own equipment for certain specialized operations.
Business analysis studies and experience of certain Florida
nurserymen show that properly chosen and employed mechan-
ical equipment will contribute greatly toward maintaining or
increasing profits by saving time and by reducing labor costs.
However, operational and maintenance costs of mechanical
equipment and volume of plant units or materials handled must
be considered together. Labor saving equipment can lose money
for the nurseryman if volume to be handled does not keep ma-
chinery and crews busy for a profitable period of time. Mechani-
zation in whole or in part will likely cost less now than at some
time in the future because of inflation, and advantage can be
taken of reduced costs of the machine performed operations.
Generally, it costs less to utilize mechanized equipment from the
start of a nursery operation than it does to revamp an estab-
lished operation to accommodate a new device.
A must in mechanical equipment is a properly designed irri-
gation system (See irrigation and soil moisture section). The
irrigation system should be designed to: (a) adequately water
the plants; (b) apply liquid fertilizer and other materials; and
(c) provide for frost protection. (See temperature relation-
ships section.) A serious disadvantage of the tube or individual
container system (trickle system) of irrigation is that it cannot
be used to provide frost protection.
MEDIA PASTEURIZATION AND PASTEURIZATION-MIXING EQUIPMENT
Many procedures have been proposed for pasteurizing bulk
soil. Various types of movable and in-place equipment have been
developed for this purpose, including flame sterilizers, steam
forks and rakes, adaptations for applying steam to media being
mixed in concrete mixers, and boilers adapted for supplying
aerated steam to maintain media temperatures at 1600F. Usually
systems using low-pressure boilers are more economical than
those using high-pressure sources of steam.
A good media pasteurization system must provide (a) a
means for heating all of the medium to a minimum of 1600F,
and holding it at this temperature for at least 30 minutes and
(b) storage areas and handling equipment which can be kept
sterile to prevent recontamination.
The Florida Cooperative Extension Service (95) has devel-
oped a media pasteurizer-mixer that does a good job of simul-
taneously mixing and pasteurizing potting media. When pas-
teurization and mixing are combined, the capacity is approxi-
mately 2 cubic yards per hour. In mixing only the output is
nearly 5 cubic yards per hour. This equipment can be made in
a machine shop, and construction plans are available from the
Florida Cooperative Extension Service.
MEDIA MIXING AND PLANT POTTING EQUIPMENT
Preparing potting media, potting plants (potting rooted
cuttings, liners, or larger plants), and painting cans are other
production operations that are labor and time consuming and,
therefore, influence production costs.
There are three methods generally used for mixing ingre-
dients of potting media. In order of effectiveness they are: (a)
cement mixer (type used on ready-mix trucks) mounted on a
stationary base; (b) shredder-mixer, which may be purchased or
rented; and (c) front-end loaders, which are the least efficient
of the three methods. Advantages and limitations of these types
of media mixing equipment are discussed in the section on
growing media. Automatic potting machines and service con-
veyors are available which will save labor, but their economical
use is based on handling large volumes of plants. A machine for
painting cans is available for nurserymen who purchase un-
painted cans. Any combination of the basic units, for example
those used in mixing the potting medium, should be beneficial.
The operation can later be expanded to include other units.
FERTILIZER APPLICATION EQUIPMENT
In order to benefit from time and labor saving procedures
when adding fertilizers to potting mixtures at time of mixing
(see fertilization section), some type of metering and mixing
equipment is required. All media ingredients and chemical addi-
tives must be well-mixed to obtain maximum plant growth re-
sponse. However, thorough mixing on a large scale can be
accomplished only with mechanical equipment such as that dis-
cussed in section on growing media.
When fertilizing container nursery plants through the irriga-
tion system, a mechanical injector (several types are available
on the market), or other equipment which accomplishes the same
purpose, is used to inject the liquid fertilizer and/or pesticides
into the irrigation system. Information on this type of equipment
is given in Florida Cooperative Extension Service Circular 276A,
A trap-door type of hand applicator can be used to place dry
fertilizer in containers with less expense than by the old "spoon"
The Georgia Experiment Station has recently designed and
built a chemical dispenser for use in applying fertilizers and
other chemicals used for insect and weed control to containers.
Their tests show that this equipment has the advantages of:
(a) personnel comfort laborers can use it while in an erect
position; (b) giving a more accurate measurement and place-
ment of amount applied; and (c) saving of over 200% in appli-
cation time, as compared to the old "spoon" method.
A drop type of fertilizer spreader has been successfully used
to apply dry fertilizer to small plants in nursery beds.
Recently it has been suggested that pelleted fertilizers may
be applied to container plants with hand operated cyclone
spreaders. The efficiency of this type of application has yet to be
PEST CONTROL EQUIPMENT
Various emulsifiable pesticides are being applied through
irrigation systems by using various types of metering and appli-
cation equipment. Equipment for applying these materials must
be carefully monitored to reduce loss or problems resulting from
poor mixing and distribution.
The nurseryman should consult the entomologist, plant pa-
thologist, agricultural engineer, and commercial men in the field
for advice as to the best and most effective equipment for pest,
and weed control problems.
HAULING WITHIN NURSERY
Some type of truck with a platform body, or small tractor
and platform trailer, is needed to move equipment, materials,
and potted plants in and out of bed areas of the nursery. The
number needed must be determined by size of the nursery. The
Florida Cooperative Extension Service has developed a small
platform trailer for use with small tractors that will follow in
the same tracts, when turning corners, as the towing tractor.
This equipment can be made in a machine shop, and construction
plans are available from the Florida Cooperative Extension
PRUNING, TRAINING, AND SPACING NURSERY PLANTS
PRUNING AND TRAINING
Pruning is the reduction or removal of certain plant parts
that are no longer required or are ineffective in production
growth, thus diverting energy to other parts of the plant. There
are several objectives of pruning for the commercial nursery-
man. One objective is to get as large a plant as possible, as
quickly as possible, and at the same time, obtain a healthy plant
with a form or shape that will sell. Usually this means a plant
that is dense, compact, symmetrical, healthy, and vigorous, and
one which is produced and sold at a profit. A second objective of
pruning is to produce a plant that transplants successfully,
whether planted by a landscape contractor or homeowner.
Definite rules for pruning ornamental plants in a nursery are
hard to give because plants vary widely in habit of growth.
Pruning is both a dwarfing and an invigorating cultural prac-
tice, depending on how and when the heading back, thinning, or
pruning is done. Summer pruning may increase the number of
growing twigs or branches, but reduce food manufacturing
ability of the plant. Pruning in late winter or very early spring
may reduce plant growth less because much of the food stored
in the branches will have been translocated to the roots, and will
not be removed by pruning. Heavy pruning of the top usually
reduces root growth more than it does top growth. Usually a
larger plant can be produced faster with minimum pruning, as
severe pruning produces a smaller but more dense plant.
The natural growth habit of a plant indicates the pruning
needed to shape the plant. No plant, regardless of growth habit,
should be pruned by "first rounding the sides of the plant and
then rounding off the top."
Generally, two types of cuts are made in pruning plants in
a nursery. Cutting back or "heading back" involves cutting a
branchlet or a side branchlet back to a point somewhere between
the tip and the base of the branchlet or branch. "Heading back"
stimulates or increases number of "breaks" or buds that grow
near the cut, thus increasing density of the plant at point of
pruning. As number of breaks arising from a pruning cut in-
crease, the shorter each twig is likely to be.
Thinning involves removing the entire branch or branches
back to a side branch or branchlet. This type of pruning de-
creases the number of branches or growing points, and thus
increases amount of nutrients and water going to the remaining
growing points. This increases the vigor of these branches or
twigs, though total growth of the plant may be decreased.
Pruning tops of plants reduces growth by reducing the manu-
facture of plant food due to loss of leaf area.
Because pruning is both a dwarfing and an invigorating pro-
cess, the commercial nurseryman is interested in a combination
system of pruning, which includes both heading back and thin-
ning. This consists of heading back to increase density of thin
plants, thinning areas of an otherwise dense plant, and thinning
of dense growth to produce a plant that is taller and wider than
it would be if not pruned.
Effective pruning of nursery plants begins with selection of
the cuttings as well as pruning practiced early in the life of
plants propagated from cuttings or seedlings. A compact con-
tainer grown plant can be produced more easily from large 4 to
6-inch cuttings than from smaller 1 to 2-inch cuttings. Smaller
cuttings sometimes root faster, but take longer to produce plants
to the size where heading back is done to increase density of the
potted plants. However, a 4 to 6-inch cutting usually has enough
leaves to produce good rooting, and because of this will reach
the stage sooner where pruning is begun to produce well
branched plants. When transplanting rooted cuttings, excessively
long roots should be cut back. This will encourage branching
and growth of new roots, and reduce development of kinked,
girdling, and circling roots.
Liners and seedlings of species trained as shrubs should be
pruned early and frequently to produce "breaks" low on the
main stem to encourage a good production and distribution of
The commercial nurseryman should carefully examine his
pruning procedures because they are expensive and time con-
suming operations. Much less time is required to prune small
plants than larger ones. The main scaffold branches should be
formed early so later growth will be well distributed over the
plant and more easily controlled. Young plants should be pruned
as often as needed to produce the branching necessary for a high
quality plant. The number of times pruning will be required
from first potting until plants are sold will vary depending on
several factors: (a) plant species; (b) fertilization level; (c)
time plants remain in the nursery; (d) size of container; (e)
climatic locality as it affects length of growing season; and (f)
time of year plants are potted. A combination of "heading back"
and thinning should be practiced on older plants to produce com-
pact growth in the natural shape of the plant rather than to
indiscriminately shear all plants regardless of growth habit,
density, or size.
Corrective pruning of shade trees should begin early to en-
courage development of a central leader on most trees, a low
center of gravity for branching of a multiple-leader tree, and
growth of permanent scaffold branches. Lower branches should
be left on the trees until they interfere with cultivation or de-
velopment of the plants. Branches should be left all along the
trunk on specimen trees, but should be thinned to form a well
spaced scaffold branch system.
Thinning may be used to increase size of flowers and fruit
by reducing the number of flowering branches after buds have
developed. This is accomplished by increasing the amount of
water and nutrients available for flower buds left on the plant.
"Heading back" plants before flower buds are set increases the
number of flowers, but will usually reduce flower and fruit size.
Plants to be used for hedges and barriers should be headed
back early and often to cause formation of dense intertwining