I ,Ornamental Horticulture Report 70 1
JUL 2 0 1972
in florida -
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
Appreciation is expressed to the many people who contributed infor-
mation and especially those that reviewed this manuscript on leatherleaf
fern. Without the aid of Dr. J. N. Joiner and Mr. R. D. Dickey, Ornamental
Horticulture Department, Mr. D. S. Harrison, Agricultural Engineering
Department, Mr. J. E. Brogdon and Dr. D. F.'Short, Entomology Department,
Dr. R. S. Mullin, Plant Pathology Department, IFAS, University of Florida,
Gainesville, Drs. W. E. Waters, R. T. Poole and J. F. Knauss, Ridge Orna-
mental Horticultural Laboratory, IFAS, Apopka, Mrs. A. J. Overman, Gulf
Coast Experiment Station, IFAS, Bradenton and Dr. S. A. Alfieri and Mr. G.
W. Dekle, Division of Plant Industry, Gainesville, this information could
not have been assembled.
Table of Contents
INTRODUCTION . . . . . . . . . . . 1
CULTIVARS . . . . . . . . . . . 1
SITE SELECTION . . . . . . . . .. . . . 2
LIGHT REQUIREMENT . . . . . . . . .. . . 4
STRUCTURES . . . . . . . . .. . . . . 4
SOIL PREPARATION . . . . . . . . . . . 7
PLANTING . . . . . . . . .. . . . ... .9
FERTILIZATION . . . . . . . . .. . . . 10
IRRIGATION . . . . . . . . .. . .... .. 15
TEMPERATURE CONTROL . . . . . . . . ... ... .15
WEED CONTROL . . . . . . . . ... . . .17
NEMATODE CONTROL . . . . . . . . .. . . .18
INSECT CONTROL . . . . . . . . . . . .21
DISEASE CONTROL . . . . . . . . . . . 22
ANIMAL AND RODENT CONTROL . . . . . . . ... .25
HARVESTING . . . . . . . . ... . . . .25
MARKETING . . . . . . . . ... . . . . 26
LEATHERLEAF FERN PRODUCTION IN FLORIDA
Charles A. Conover and Larry L. Loadholtzl
Florida leads the United States in production of leatherleaf fern,
with approximately 1000 acres in production. Estimated value of the 1969
crop was about 7 million dollars. This did not reflect the true potential
of 1000 acres since at least 25 percent had been planted less than one year.
Small amounts of leatherleaf fern were produced in Florida during the
1930's and 1940's, but major plantings were not started until the early 1950's.
The rapid production increases are not related to improved methods of produc-
tion, but to a change by commercial florists from Asparagus plumosa plumosaa
fern) to leatherleaf fern in their floral arrangements. This change is due
primarily to the better keeping quality of leatherleaf fern, and to a change
in consumer preference concerning leaf shape and texture.
The main production area for leatherleaf fern is Volusia County, but
considerable production also occurs in Putnam, Lake and Orange counties.
Small plantings of leatherleaf fern can be found throughout Florida on sandy,
well-drained soils, even in northern sections when winter production is provided.
The commercial leatherleaf fern grown in Florida is Polystichum
adiantiforme, and is a rhizomous herb native to tropical areas of South
Assistant Ornamental Horticulturist, Cooperative Extension Service, University
of Florida and Ornamentals Extension Agent, Cooperative Extension Service,
America, South Africa and New Zealand. There is much confusion within the
industry concerning cultivars and growers generally acknowledge three dis-
tinct types. This is probably true, but botanical nomenclature does not
substantiate these observed differences.
Grower-named cultivars of leatherleaf generally associated with quality
fern are the selections 'Baker' and 'Mayfield'. These selections both
produce fronds that are heavy, have large sturdy mid-ribs and a deep, dark,
glossy green color. However, even these better selections will be of poor
quality unless proper growing conditions are provided.
There are two less desirable selections of leatherleaf fern grown by
a few producers. 'Curley leaf' has curly fronds and poor color which does
not sell well. The other less satisfactory selection 'Light stem' is
characterized by light weight stems which have little substance, poor color
and rapid growth. Due to poor stem rigidity and other factors it does not
have the market demand typical of 'Baker' and 'Mayfield'.
Leatherleaf fern used for planting stock should be of the 'Baker' or
'Mayfield' selections. Fern with curly or light-weight fronds, poor rigidity
or poor color should not be used for planting stock, no matter what the
Leatherleaf fern can be grown from Jacksonville south, but warm loca-
tions should be selected or provision made for protecting plants during cold
weather. Mature fronds are injured when temperatures drop below 280F., even
though rhizomes survive lower temperatures. Except for small protected
plantings for local sales the northern limit for commercial plantings is
south of an east-west line through Ocala and Palatka, Florida.
High, sandy, well-drained soils are best for production of leatherleaf
fern, although soils with clay or organic matter present are also excellent
provided internal drainage is good. Leatherleaf fern requires considerable
moisture for best yield, but it cannot tolerate standing water or saturated
soils for more than 6 to 12 hours without damage. Rapid internal and sur-
face drainage necessary for production of leatherleaf fern is usually
associated with soil types 1, 2, 3, 4, 5, 8, 9, 12 and 17. (See general
soil map of Florida 1962 available from the soil conservation service).
These sandy soils are moderately to excessively drained and can be used
without need for ditching and tile drains. Even in these soil types areas
that form pockets without surface drainage to lower areas should not be used.
Soil types 1 and 2 have lower water and nutrient holding capacities and
therefore are less satisfactory than other types unless amended. Leather-
leaf plantings are also successful on sandy lower elevation soils when they
are tile drained.
Leatherleaf fern requires shade for quality production and, until
recently, many growers selected sites with natural oak shade. This is
initially a low-cost source of shade, but long-run costs are increased
because of pruning, plant competition, insect problems, pesticide toxicity
to trees and obstacles to mechanization. Therefore, even though natural
oak shade might be acceptable for small plantings it is not recommended for
Other factors of importance in site selection include land cost, labor
availability, transportation and a good water supply.
Future growth of the leatherleaf fern industry in Florida will continue
in Volusia, Putnam, Lake and Orange counties because most requirements of
site selection can be easily obtained there. However, other areas that can
provide many of the necessary requirements include parts of counties along
the central and southeast coasts, from Orlando to Lake Placid in the ridge
section and in parts of counties on the west coast south of Dunellon. Small
plantings for local sales can be located wherever well-drained soils can be
The exact light level required for production of leatherleaf fern has
not been determined because it is influenced by fertilizer and watering rates.
In general, fern grown under heavy shade (80% or more) will develop a dark,
green color and a flat leaf on fairly low fertility regimes, but production
will be low. Fern grown under medium shade (65 to 70%) requires higher
fertility levels to obtain the same color, but quality and production will
be higher. Fern grown under less than 60% shade will be light green and
fronds tend to be thick and curly. Considering light levels in Florida on
a yearly basis the best percent actual shade to provide is about 65 to 70
percent. Determination of shade levels provided by oak tree shade is diffi-
cult, and is best done with the aid of a light meter capable of reading in
foot-candles. Table 1 provides approximate maximum obtainable light levels
in foot-candles under saran or polypropylene shade during different seasons.
Structures will include all methods of providing shade for leatherleaf
fern including trees, brush covered sheds, slat sheds, and saran and poly-
propylene covered shade houses. Each method of providing shade has some
advantages and disadvantages. Irrigation is necessary with all growing
structures and is discussed in the irrigation section.
Tree shade -- At present about 50% of leatherleaf fern production
is under oak shade, but this method is decreasing. A site shaded by trees
has the disadvantage of competition from trees for water and nutrients,
and in addition they serve as obstacles to mechanization, use of herbi-
cides, fumigants and some types of heating systems. Shade provided by
trees is variable and cost of pruning and damage to ferns during pruning
is high. Almost all new ferneries being established do not use trees for
shade. When trees are used for shade they should be pruned during summer
months to obtain an average of 3000 to 4000 foot-candles of light at noon.
Slat sheds -- A considerable amount of leatherleaf fern is grown
under slat sheds, primarily because it has replaced plumosa fern. Cost
of materials and labor has made construction of new slat sheds expensive
for production of leatherleaf fern, but these sheds do provide an excellent
source of shade. When new sheds are built or old ones repaired, slats
should be spaced to provide about 65 to 70 percent shade or 30 to 35 percent
Brush covered sheds -- Many sheds covered with rosemary (Ceratiola
ericoides) can be found in the fern producing areas. These sheds create a
fire hazard, especially during winter months if open flame heaters are used
around the fernery, since rosemary contains a volatile oil. Few new sheds
being constructed use this material since it is scarce near fern-producing
areas and is expensive to gather. Sheds built for covering with rosemary
have posts set 10 to 12 feet apart, with 1 x 4 or 2 x 4 inch lumber stringers
tying them together at the top. The structure is then covered with gal-
vanized chicken wire of about 2 inch mesh and rosemary placed on top of the
wire, until the desired shade level is obtained.
Saran and polypropylene shade houses -- This type of construction is
most common in new ferneries and in additions to old ferneries where
expansion is occurring. Initial costs are higher than some of the other
methods of shading fern, but it pays off with time in reduced operating
costs and improves yield and quality. In addition, this type structure is
easy to cover with plastic during winter months for cold protection.
Construction of saran or polypropylene shade houses is basically the
same as other type sheds, but growers use minor variations in post spacing,
lumber type and size. Generally, 10 to 12 foot long posts are spaced ap-
proximately 10 to 12 feet or more on centers and tied together at the top
with 1 x 4, 2 x 4 or larger stringers. Size of the stringers depends on
post spacing; 2 x 4 inch stringers are satisfactory for 12 foot spacings or
less, but heavier lumber must be used with wider post spacings. Another
method of construction utilizes posts on the same spacing, but instead of
stringers the posts are tied together with heavy galvanized wire of about 8
gauge. The shade cloth is attached either to wood stringers with tack-strips
or to wire with nylon cord or S-hooks.
Table 1. Approximate maximum obtainable foot-candles of light received under
various percentages of shade during different seasons in Florida.1
Season of year
Actual shade Winter Spring Summer Fall
provided (Dec.-Jan.-Feb.) (Mar.-Apr.-May) (June-July-Aug.) (Sept.-Oct.-Nov.)
(Full sun) 8,700 15,300 15,900 11,600
50% 4,350 7,650 7,950 5800
60% 3,480 6,120 6,360 4,640
70% 2,610 4,590 4,770 3,480
80% 1,740 3,060 3,180 2,320
1Weather forecasting Service, Gainesville, Florida
Clearing -- When fern plantings are to be made utilizing oak shade,
underbrush, stumps and pine trees should be removed. Removal of pines during
the clearing phase is easier than removal later, after they have died from
high fertility levels necessary for growth of fern or disease or pesticides.
Modern production methods are not adapted to oak shade ferneries, and there-
fore, complete clearing is recommended rather than the above procedure. The
trees, stumps and brush should be burned in an area that will not be immedi-
ately planted to fern due to high levels of some fertilizer elements in the
Soil amendments -- Use of well drained, sandy soils for fern production
creates problems with maintenance of proper soil moisture and nutritional
levels. Amendments are used to improve soil physical condition, aeration,
and moisture and nutrient holding capacities. Amendments are grouped as in-
organic and organic. Inorganic amendments include calcined clays, perlite
and vermiculite, although they do not decompose in the soil, they are too
expensive for use in fern production. Organic amendments easily obtained in
Florida include bagasse, peat moss, garbage compost, shavings, sawdust and
pine bark. Local availability and cost per cubic yard usually determine
feasibility of using a particular amendment. Amendments containing high
levels of cellulose, such as sawdust, shavings and pine bark, will have to
be supplemented with nitrogen to prevent tie-up of available nitrogen in the
Organic amendments are suggested for us- in fern plantings and a 1 1/2
to 2 inch layer should be added to planting beds and rototilled to a depth of
6 inches. Average particle size of the amendment used should allow good
drainage and aeration when mixed with native soil.
Leatherleaf fern can be grown in sandy soils without the addition of
soil amendments, but high quality fern is more difficult to produce under
these conditions. The low "buffer" capacity in the soil causes large
changes in pH and soluable salts from the addition of fertilizers. Ferti-
lizer programs must be designed to supply small amounts frequently, since
sandy, non-amended soils are less retentive of fertilizer nutrients.
Watering is also more critical in non-amended soils, as less water is held
for plant growth and more frequent irrigation is necessary, further compli-
cating the fertilizer retention problem.
Needed calcium, magnesium, phosphorus and micro elements should be
mixed into the soil with the soil amendment. Most virgin Florida soils need
at least 2,000 pounds of dolomite and 1,100 pounds of superphosphate per
acre (4 1/2 lbs. dolomite and 2 1/2 lbs. superphosphate per 100 sq.ft.) to
add calcium, magnesium, phosphorus and sulphur. In addition, 25 pounds
copper sulphate, 25 pounds zinc sulphate, 50 pounds manganese sulphate and
25 pounds iron chelate should be added per acre to amended virgin soils. A
micro element mix may also be used, provided rates are similar.
In order to determine quantities of dolomite and superphosphate nec-
cessary for soils already in cultivation and for more accurate recommendations
on virgin soils, samples should be taken to determine initial levels of
these elements. The most desirable pH is in the range of 5.5 to 6.0, there-
fore, if pH is below 5.0, add 1/2 to 1 ton of dolomite per acre. Based on
the ammonium acetate procedure of soil analysis used by the University of
Florida, where calcium levels in the soil are low and pH is high, use calcium
sulphate (gypsum) to raise the calcium level to at least 1000 pounds CaO per
acre. Soil magnesium level should be at least 250 pounds MgO per acre and
phosphorus at least 50 to 80 pounds P205 per acre. Soil amendments, liming
materials and superphosphate should be thoroughly incorporated into
planting beds to a depth of 6 to 8 inches.
Soil fumigation Fumigation of planting areas is not recommended
at the present time due to lack of information on this aspect of pro-
duction. Growers who might desire to establish a trial planting on fumi-
gated soil for disease, nematode and weed control may use methyl bromide
at 1 1/2 to 2 pounds per 100 sq. ft. or Vorlex-201 at 1/2 to 2/3 gallon per
600 sq. ft. Be sure to follow label directions on waiting period prior to
planting previously dipped fern rhizomes or nematode free fern.
After soils are amended and rototilled, planting beds should be oriented
in a north-south direction and elevated about 4 to 6 inches above aisles to
aid drainage. Beds should not be wider than 4 feet to aid in maintenance
and help prevent workers from walking in beds which damages fern and causes
disease spread. Bed widths of 3, 3 1/2 and 4 feet are commonly found in the
industry with the narrower beds being most popular. Aisle widths also vary,
but 2 1/2 to 3 foot aisles seem satisfactory.
Plant spacing within beds is usually 12 x 12 inches, but some growers
utilize a spacing of 18 x 12 inches. The wider spacing is more conservative
of planting material and delays the time when overcrowding will occur, how-
ever, production will be lower the first 1 to 2 years. Production infor-
mation is not currently available on the various spacing systems used.
Plants should be planted approximately 1 1/2 inches deep, as deeper plant-
ing causes delay in establishment and shallow plantings dry too easily.
Plantings should be established with the best quality rhizomes
available. Planting stock should have rhizomes 4 to 5 inches in length with
2 to 3 healthy fronds and an uninjured terminal bud. Larger clumps with
2 or more rhizomes may be used for more rapid establishment if planting
stocks are available at low cost. Fern grown from spores should not be
used, due to variation between plants (such plants probably will not be
of the 'Baker' or 'Mayfield' type) and because it takes about 3 years for
spores to produce plants large enough for fronds to reach cutting size.
Damaged fern rhizomes can be saved and disked or set in a nursery block
where they will make satisfactory planting stocks after about 1 to 2 years.
Leatherleaf fern is produced in Florida under many fertilizer regimes,
but proper fertilization programs will improve quality, lengthen keeping
time in the home and produce high yields per square foot. Rates of ferti-
lization should be varied depending on light levels, type of soil and type
of shade. More information needs to be obtained on leatherleaf fern ferti-
lization and the best available is presented. Table 2 provides information
on foliar nutritional levels associated with leatherleaf fern. Granular
fertilizers applied overhead may cause foliar injury if applied to wet
foliage. Therefore, they should be applied to dry foliage and the residue
washed from fronds as soon as possible. Fern should be irrigated overhead
for about one hour to move fertilizer into the root zone.
Fertilizer sources -- Several types of fertilizers, including inorganic,
organic and slowly soluble or slow-release fertilizers are available. In-
organic sources of fertilizer are recommended because they are readily a-
vailable, low in cost, and easy to apply through irrigation systems or with
mechanical distributors. Where fertilizers must be applied by hand, organic
or slow-release forms are recommended during warm months to conserve labor.
Availability of nutrients in organic fertilizers depends upon environmental
factors such as soil temperature, moisture and microbial populations.
Table 2. Chemical composition of mature leatherleaf fern fronds based
on dry weight giving low, desirable and high ranges of elements.
Element (less than) Desirable range (more than)
% % %
Nitrogen 2.0 2.2 to 3.0 3.2
Phosphorus 0.2 0.25 to 0.50 0.6
Potassium 2.3 2.5 to 3.8 4.0
Calcium 0.25 0.30 to 0.80 1.0
Magnesium 0.28 0.20 to 0.40 0.5
ppm ppm ppm
Boron 20 25 to 75 100
Copper 8 10 to 30 40
Iron 75 100 to 200 250
Manganese 25 50 to 150 200
Zinc 20 25 to 100 150
These averages have been obtained by sampling good and poor quality fern,
and is a compilation of information from analysis by the Ornamental
Horticulture Department and International Minerals Corporation.
Fertilizer ratios -- Proper fertilizer ratios depend on previous ferti-
lization practices. Generally, phosphorus accumulates in sandy soils with
a pH in the range of 5.5 to 6.5 and is needed by plants in lesser amounts
than nitrogen and potassium. On land where the residual phosphorus level
is not too high a 2:1:2 ratio fertilizer can be used such as 8-4-8. Gener-
ally, this ratio is satisfactory as long as phorphorus does not accumulate
and interfere with micro element uptake. Soils with high phosphorus levels
(above 150 pounds P20 /A) should be fertilized with materials having a 1:0:1
ratio or close to it such as 8-0-8 or 20-2-20. Some virgin soils with low
pH levels (below 5.5) may be low in phosphorus and a 1-1-1 ratio fertilizer
such as 8-8-8 or 20-20-20 may be used until phosphorus levels increase.
Fertilizer rates -- Recommended rates are determined by rate of plant
growth, light level and other environmental factors. Fern growing under
light levels recommended in this publication (approximately 3000 to 5000
foot-candles depending on season) should receive more fertilizer than fern
growing under 2000 to 3000 foot-candles. Therefore, rates listed in Table
3 can be reduced by 25 to 30 percent if fern is grown under heavy shade
(approximately 80%). Leatherleaf fern grown on sandy, unamended soils and/or
under oak-tree shade where more competitive growing conditions exist should
receive the higher rate listed in Table 3. Generally, the fertilizer rate
should be decreased from 30 to 50 percent during the winter months (December
through February) when low temperatures prevail and growth is reduced un-
less protected and heated.
Table 3. Fertilizer recommendations for leatherleaf fern
60 to 70 percent shade
Fertilizer Rate Rate
element Ibs/acre/month lbs/1000sq.ft./month Remarks
50 to 60
25 to 30
50 to 60
1.2 to 1.4
0.6 to 0.7
1.2 to 1.4
Use sources to pro-
vide 1/2 in ammon-
ium and 1/2 in nitrate
Use a lower rate if
soil level is high.
A high chlorine con-
taining source is
Apply once or twice
a year to maintain
1000 to 1500 lbs
CaO per acre.
Apply monthly, or
at 6 times this
rate once each 6
Microelements -- Exact levels of microelements required by leatherleaf
fern are not known at present. However, fern deficient in iron and manganese
has been found in a number of ferneries where they have not been soil incor-
porated. In some growing areas, it will be necessary to use fertilizers
containing microelements, but continual use is not recommended due to increased
cost and possible build-up to toxic levels in soil. Growers should remember
that microelements such as iron, manganese and zinc may be included in fungi-
cidal sprays and adjust microelement fertilization accordingly.
Soluble salts -- Leatherleaf fern is intolerant of high soluble salt
levels in the soil. Injury occurs first to roots and is characterized in
above ground portions of the fern by temporary wilting of young fronds, margi-
nal burning of young or recently matured growth and various chlorosis patterns
indicative of microelement deficiencies.
Factors affecting soluble salt level includes watering practices,
salinity of water and fertilization programs. Method of watering and soil
moisture levels affect soluble salts, and where salinity is a problem high
soil moisture should be maintained. Medium to high soil moisture reduces
salt concentration, for example, a soil containing 500 ppm soluble salts at
50% soil moisture will contain approximately 1,000 ppm soluble salts at
25% soil moisture. To prevent possibility of damage from soluble salts,
leatherleaf fern should never be allowed to become too dry, especially if a
high fertility program is followed.
Irrigation water containing large amounts of soluble salts should not
be used for watering leatherleaf fern, but water with salt levels as high as
800 ppm can be used provided sufficient leaching occurs each time the crop
is watered. Irrigation water with 500 ppm soluble salts or less are considered
best for leatherleaf fern production.
The last primary source of soluble salts is an incorrect fertilizer
program. Sources of various fertilizers and essential elements are almost
always salts, such as potassium nitrate and ammonium nitrate. When such salts
are added to the growing medium the osmotic (salt) concentration of the
soil solution increases. If this concentration exceeds the osmotic con-
centration of plants cells comprising absorbing root hairs, water will be
withdrawn from the roots. Therefore, the fertilizer program must supply the
right amounts of fertilizer at sufficient frequency to prevent application
of too much atd at one time.
Growers having excessive soluble salt levels in their growing medium
should take corrective measures as soon as possible to prevent damage to
their fern. Irrigate heavily to immediately lower soluble salts to a level
that can be tolerated. Amounts of water needed depend on the degree to
which soluble salt level is to be reduced. Generally, for each square foot
of soil to be leached six inches of irrigation water leaches out one-half of
the salt and 12 inches four-fifths of the salt.
Red-edge -- This problem is due to a calcium deficiency in leaf tissue,
and is corrected by maintenance of proper soil calcium levels. Soil calcium
level should be maintained at about 1000 pounds of CaO per acre to prevent
this deficiency from occurring -- additional information on calcium levels is
given in the soil amendment section and in Table 2.
Red-edge can be corrected quickly on developing fronds by application
of 5 pounds of calcium nitrate per 100 gallons of water sprayed per acre of
fern. However, addition of calcium to the soil will be necessary to obtain
permanent control and weekly foliar applications will be necessary until soil
calcium is available. Application of calcium will not improve the condition
of old fronds, but new fronds should develop normally.
Red-edge type symptoms can be caused by other factors including nutrition,
soluble salts and other abnormalities, but these are generally brown, rather
Irrigation of leatherleaf fern is necessary to produce quality crops,
since water stress in a plant -- even if it occurs for a short time --
reduces growth. The amount of water to apply depends on soil type, shade
level, humidity, wind speed and temperature. Generally, one inch per ap-
plication is necessary during hot summer months. Frequency of irrigation
and amount of water to apply each time must be adjusted to keep soil moist,
not saturated to the depth of the root system. Watering lightly and fre-
quently leaves soil in the lower root region dry and reduces root and top
growth, while over-watering leaches fertilizer from the root zone.
Overhead irrigation is the best method of applying water to leatherleaf
fern. Such systems should be set up to obtain a 100 per cent over-lap, so
that they will also be satisfactory for application of liquid fertilizers and
as an aid in cold protection. Generally, ferns require an average of one
inch of water every 3 days during summer months and one-half inch every 4 days
during winter months when growth is restricted and temperatures low.
Complete information on overhead irrigation systems for leatherleaf
fern can be found in Cooperative Extension Service Engineering Mimeo Report
63-2, (Revised), "Irrigation Design for Leatherleaf and Plumosus Fern in
Florida". Copies are available from your Cooperative Extension Agent.
Leatherleaf fern is not injured until temperatures in the fernery
drop below 30"F. Numerous methods, such as various types of oil heaters,
open fires and sprinkler irrigation are used to protect ferns from freezing.
Each method has advantages and disadvantages.
Open flame oil heaters such as the open furnace, single cone and
return stack types provide some protection, but cause considerable fern
damage during filling operations, and are dangerous to structures. This
method is still being used in a number of operations and is better than no
protection at all.
Research has shown recently that leatherleaf fern could be protected
with sprinkler irrigation by utilizing the latent heat of fusion. When
liquid water turns to ice, 80 gram calories of heat are released per gram of
water and if water application'is continuous during the freezing period the
constant release of this heat will maintain temperature of the fern frond
at approximately 320F. Low angle, double headed sprinklers must be used,
the supply of water must be constant, and at least 0.3 acre inches of water
must be supplied each hour for this system to work properly. The irrigation
system must be started when the temperature is 32 to 340F. and continuously
operated until ice from the freeze has melted or the wet bulb temperature has
reached 320F or greater.
Sprinkler irrigation used for freeze control is effective and fairly
economical, but has a number of disadvantages. If the irrigation system is
not operated continuously throughout the freezing period fern damage may be
greater than if the sprinkler system was not used. This occurs when foliage
with ice reach the "wet bulb" temperature which may be 2 to 10 degrees F
below "dry bulb" temperatures due to evaporational cooling. Increased damage
may also occur if insufficient water is applied to keep up with the amount
that is freezing. Application of large amounts of water necessary to prevent
freeze damage during severe freezes may cause serious root and rhizome damage,
soil erosion, destroy soil structure and leach nutrients out of the root zone
including phosphorus, calcium and magnesium as well as nitrogen and potassium.
Therefore, this method of cold protection is decreasing in popularity with
Covering ferneries with lightweight two mil. polyethylene is the most
recent and best method of protecting leatherleaf fern from frost. This
method is also useful in increasing production during winter months when ferns
bring the best price. Polyethylene is applied inside the fernery by tacking
it to sides of stringers between posts and pulling it tight. While poly-
ethylene is still in the roll 1/2 inch holes should be made about 12 inches
on centers with an electric drill, this will allow rain water to run through
and prevent water pocketing which can destroy the structure. Polyethylene
should be attached inside the growing structure about the middle of November
and removed during late March. High day temperatures inside the fernery
can be controlled by attaching polyethylene to outside walls so that it can be
rolled up during high-temperature periods to allow ventilation. Loss of heat
through the holes is negligible, but additional heat is sometimes necessary
to prevent freezing during severe cold and to obtain good winter production.
Many sources of heat can be used satisfactorily, but LP or natural gas, if
free from impurities, seems the best heat source. In addition, these
sources provide CO2 as well as other impurities. The disadvantages to covered
structures are cost of polyethylene, labor and heating costs. However,
increased winter production due to lack of frost problems and more favorable
growing temperatures offset these costs and guarantee a steady supply of fern.
Cultivation is still a good method of controlling weeds in young
leatherleaf plantings since fern that is not established is more easily in-
jured by herbicides. Any measure that will aid in preventing contamination
of planted areas with weed seed should be practiced. To control weeds that
germinate during the first 6 months light cultivation in aisles with roto-
tillers and within rows with small "sweep-type" cultivators or hoeing
At the present time, no herbicides (chemical weed killers) are regis-
tered for use on leatherleaf fern plantings. However, Simazine has been
used for a number of years with success in a large number of ferneries.
Simazine has been applied at the rate of two pounds of active ingredient
per acre, but should not be applied to fern until 6 months after planting
and then not more than once every 6 months. Granular Simazine has proved
most satisfactory and can be used in any type of fernery, including those
under oak shade. Misuse of Simazine will cause stunting of leatherleaf
and, therefore, the listed rate should never be exceeded.
Paraquat, a contact herbicide that kills green vegetation that by
contact can be used for spot or aisle treatment if a directed spray is
used to prevent contact with fern. This material has been used with satis-
factory results at a rate of 1/2 pound active ingredient per acre. For
small areas, 2 teaspoons of Paraquat per gallon is effective. Do not allow
inexperienced labor to use Paraquat because drift or contact with fern will
cause brown spots on foliage, and the chemical can be dangerous to the user.
A lesion nematode, Pratylenchus penetrans, is a major problem of
leatherleaf fern in Florida. These microscopic worms seriously injure roots
and rhizomes and may predispose plants to attack by soil-borne disease
organisms. Root injury is frequently so serious that heavy nematode infes-
tations may reduce frond production by 50 percent or more. Nematode in-
fested leatherleaf fern is characterized by poor color, small sized fronds
and slow growth.
Nematodes can be controlled in bare soil by fumigation, but this is
not recommended unless clean planting stock is used, since nematode popu-
lations have been shown to increase more rapidly in fumigated than non-
fumigated soils. Nematode reinfestation of nematode free fern beds may occur
from contaminated planting stock, dirty tools and movement of infested soil
into planted areas and migration through soil. Two methods of nematode con-
trol to eliminate the possibility of reinfestation are: 1--pre-plant bare
root dips to reduce the possibility of planting contaminated stock and 2--
post-plant soil nematicidal application to kill nematodes that have become
established in planted areas.
Control of Nematodes on Leatherleaf Planting Stock In experimental
studies the materials listed in Table 4 have provided satisfactory control
of nematodes present on or in roots and rhizomes. Planting stock should be
cleaned and prepared for planting prior to dipping in chemical solutions to
prevent dipping unnecessary material. Fern should remain submerged in the
dip for 15 minutes before being removed and allowed to drain. Except for
zinophos, none of these materials have label registration and are suggested
only for trial.
Table 4. Nematocidal dips for control of Pratylenchus penetrans in
leatherleaf planting stock.
Chemical lbs. active ingredient Remarks
per 100 gallons
MoCap 1/4 No label registration at
present. However, one should
be granted in the near future.
Nemacur 1/5 No label registration.
Parathion 1/4 No label registration. Due
to high toxicity of this
material proper application
precautions should be taken.
Zinophos 1/4 See label for correct usage.
Control of Nematodes in established Leatherleaf Plantings Frequency
of application of nematicides to stock beds vary because this depends on
level of original infestation, sanitation practices and many other factors.
The best procedure is to take a nematode sample, have it analyzed and treat
if the level of nematodes is sufficiently high as to reduce production. Except
in extreme cases, more than one application a year is not recommended.
Application procedures depend on the nematicide formulation. Granular
materials can be applied broadcast to the soil surface, whereas liquid
materials should be mixed with a small amount of water and sprinkled on the
soil surface. Immediately after application of granular materials, they
should be raked into the surface and then one-half inch of water should be
applied over granular or liquid applications. Rates and materials listed
in Table 5 applied over fern have not caused injury and have controlled lesion
nematodes in experimental tests. Except for zinophos, they are listed only
Table 5 Nematocides for control of Pratylenchus penetrans in established
leatherleaf fern plantings.
Chemical active ingredient per Remarks
Furadan 10 No label clearance at
MoCap 10 No label registration at
present. However, one
may be granted in the near
Zinophos + Thimet 4 + 4 Due to high toxicity
of this material proper
should be taken.
Insect pests of leatherleaf fern can be a serious problem if allowed to
increase to high levels, therefore, many growers normally include an insecti-
cide in their spray mixture when spraying for disease control. Inclusion of
an insecticide in the spray tank each time plants are sprayed for disease con-
trol is generally unnecessary, except during periods of the year when leaf-
hoppers and caterpillars are a problem unless visible evidence of insects are
present. Thrips are thought to be a serious problem in the spring in ferneries
under oak-tree shade. Although injury to fern fronds does occur, no one has
proven that thrips in the oak flowers that drop from the trees are the cause
of the injury. The possibility exists that injury may be caused from tannic
acid leaching from the flowering oak tree catkins. Insect pests which may be-
come a problem on leatherleaf fern are listed in Table 6, with suggested con-
Table 6. Insect pests and control materials for leatherleaf
Pest Insecticide Formulation
Caterpillars Carbaryl (Sevin) 50% WP
Toxaphene 8 E
Grasshoppers Toxaphene 8 E
Leafhoppers Dimethoate 2.67 E
Thiodan 2 E
Leatherleaf Thiodan 2 E
fern borer or
Ca caterpillar) Diazinon 4 E
Spider mites Chlorobenzilate 25% WP
Tedion 25% WP
Kelthane 18.5 E
Thrips Dimethoate 2 E
Lindane 25% WP
Termites Chlordane 8 E
Slugs and Metaldehyde dust 15% dust
snails or bait
1 WP = Wettable powder, E = Emulsifiable concentrate
1 1/2 pints
1 1/2 pints
Control of fungal diseases of leatherleaf fern grown under con-
ditions of high humidity and temperature is difficult, especially during
the rainy summer season. Factors having direct effect on success of a
disease control program include the chemical used, frequency of spraying,
adequate spray pressure, proper type nozzles and adherence to good sani-
Spray schedules How often to spray depends on the initial disease
severity coupled with the continuation of favorable environmental conditions
(rain, temperature, etc.) conducive to disease development. Since the
presence of tree moisture is necessary for the development of all known fern
diseases the length of time the plants stay wet is extremely important.
Leatherleaf fern density is important in this respect since it directly af-
fects humidity and may cause foliage to remain wet for long periods. One
spray application every 2 weeks or month may protect plants in dry weather
when a low level of inoculum are present, and environmental conditions are
poor for disease development, but spraying every week or few days may be
necessary during cloudy, rainy weather when all factors which promote a
high incidence of disease are present. A fixed spray schedule is not
suggested, because during dry weather too much spray residue and possible
injury may result, whereas during wet weather too little protection may
Spray coverage Spray pressure should be high enough to obtain
good coverage and without injuring newly expanding fern fronds. Proper
nozzle arrangement for the pressure being used can be obtained through trial
and error and by observing sprayed fronds and making adjustments until
coverage is satisfactory. Poor disease control can frequently be traced to
poor spray coverage, especially on undersurface of fronds. Growers employing
irrigation systems instead of power sprayers for chemical application
should remember that this method is not recommended, and results in very
poor coverage on the under-side of fronds. This method may be satis-
factory during periods when possibility of infection is low, but will be
inadequate during periods conducive to rapid disease development. Addi-
tionally, it is very difficult to control properly disease organisms that
have become established if complete coverage of both top and under-sides
of fronds is not obtained with the chemical spray.
Concentration of chemicals Too often the tendency is to use a
higher concentration of fungicide than recommended when a serious disease
problem develops. Better disease control, however, is obtained by in-
creasing gallonage to assure coverage and frequency of spraying. Fungi-
cides are not like insecticides; they function as protectants, not era-
dicatants, and their maximum protection will result when the proper rate
is properly applied.
Sanitation Leatherleaf planting stocks are frequently a source of
disease producing organisms for the rest of the operation. New planting
stock must be healthy and diseased plants should be destroyed or removed
completely from the growing area. Even the best spray program is often in-
capable of preventing disease losses with the presence of abundant spores
from diseased plants being dispursed in wet weather.
Disease problems of leatherleaf fern can be classed as root and stem
rots and fungus leaf spots. Control methods for diseases found in each area
are different. Much more information from research is needed on diseases of
leatherleaf fern and their control.
Root and Stem Rots Loss of plants and growth reductions caused by
root rots are not known to be common in leatherleaf fern production but may
be more serious than now realized. Serious problems have occurred in some
ferneries, especially where root damage from excess water or fertilizer had
The most common fungus root and stem rots of leatherleaf fern are
caused by species of Pythium and Rhizoctonia. Symptoms of infection caused
by Pythium occur as blackening and water soaking of plant roots. Infection
usually occurs at root tips and progresses through roots to the rhizomes
causing them to collapse. Rhizoctonia causes a dry, brown, lesion type of
rot occurring anywhere on roots or rhizomes, but most frequently attacking
near the junction of fronds and rhizomes. Suppression of root rots may be
obtained by drenching plants and soil with chemicals listed in Table 7.
Table 7. Drench recommendations for control of leatherleaf root and stem rots.
Disease Amount per Frequency
Organism Fungicide Concentration 100 gallons of
of water Application
Pythium Dithane M-45 80% WP 2 pounds Every 1-2
Dexon 70% WP 1/2 pound "
Rhizoctonia Dithane M-45 80% WP 2 pounds Every 1-2
Fermate 76% 3 pounds As needed.
Fungal Leaf Spots A number of leaf spots have been identified on
leatherleaf fern and these as with other disease problems are most likely to
occur during wet, humid periods.
Generally, most fungal leaf spots start as pinpoint lesions which are
regular in outline. Leaf spots may have gray to reddish brown centers with
darker margins or of a uniform color. As spots enlarge they frequently coalesce
to form large lesions. Diseases most commonly associated with leaf spots on
leatherleaf fern are caused by the fungi Cylindrocladium and Cercospora.
Control of fungal leaf spots may be obtained with materials listed in
Table 8. Control recommendations for fungus leaf spot control on leather-
Disease 100 gallons
Organism Fungicide Concentration of water
Cercospora Daconil 75% WP 1 1/2 pounds
Rhizoctonia Manzate D 80% WP 1 pound
and others or
Dithane M-22 Spec
Benlate 50% 1/2 pound-label
or clearance unclear
at this time
Zineb 75% 1 1/2 pounds
ANIMAL AND RODENT CONTROL
Armadillos, skunks, salamanders and moles have become destructive to
leatherleaf fern plantings in some areas, especially those in or near large
wooded areas. Damage occurs at night when these pests dig or root-up plants
while searching for soil-borne insects and worms.
The easiest way to eliminate these pests is to eliminate the food
supply. Chlordane or Aldrin can be used to kill soil-borne insects, and
is most effective when soil incorporated to a depth of 6 inches. However,
surface application is also beneficial. Chlordane should be applied at 5
to 6 pounds active ingredient per acre and Aldrin at 3 to 4 pounds active per
acre. Traps for salamanders and moles are also available.
Leatherleaf fern is harvested with hand labor and there does not appear
to be a way to mechanize this phase of production. Fern "cutters" must work
through the fernery selecting and cutting only mature fronds near the soil
surface. Soft, immature fronds that have not "hardened" have poor keeping
quality and are not desired by buyers. Twenty-five fronds are placed to-
gether in a bundle and tied with elastic bands or string after harvest.
Care after cutting is important to subsequent keeping quality. As
soon as possible after cutting and bunching fern should be placed with the
cut stem ends in water, preferably in a cooler. Most fern is harvested,
crated and shipped to market by refrigerated express the same day. Infor-
mation on storage of cut leatherleaf fern is not available at this time, but
holding fronds for short periods of up to one week at 420F. has been suc-
Leatherleaf fern is packaged 40 bunches to a box or crate lined with
newspaper or cushion-paper. Lining the shipping container is necessary to
prevent bruising damage to fern and to act as insulation to keep fern cool.
Leatherleaf fern is shipped throughout the United States and many
foreign markets by refrigerated trucks, ships and airplanes. Most markets
in the U.S. are located near large population centers.
Many growers ship fern directly to wholesale distributors, while others
sell through commission markets. Some growers also ship directly to retail
florists while another method of distribution and sale is through truck sales
Growers usually find their own buyers and obtain higher profits if
they sell on a pre-arranged price.
To simplify information in "Leatherleaf Fern Production in Florida" it is
sometimes necessary to use trade names of products$ equipment and firms. No
endorsement of named products is intended nor is criticism implied of simi-
lar products which are not mentioned.