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Agricultural Sciences and should be
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site maintained by the Florida
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Copyright 2005, Board of Trustees, University
91 Circular 948
-'- INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
Fertilization recommendati ns for trees and
shrubs in home and commerciallandscapes
Thomas H. Yeager and Edwar F. Gilman ,
SUniversty of lia J .
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, dean
Fertilizer placement in relation to the plant root
zone is very important. Roots are generally thought
to occupy the soil mass directly below the tree or
shrub canopy to a depth of 18 to 20 inches. Recent
studies have indicated that root depths are usually
a maximum of 10 to 14 inches due to the naturally
high oxygen concentrations near the soil surface (1)
and more than 50% of the roots of several tree
species extend beyond the dripline by as much as
three times (2). Many roots of mulched plants are
located just beneath the mulch on the soil surface.
Consequently, for maximum utilization, fertilizer
should be applied to the soil or mulch surface.
Since most feeder roots on trees and shrubs are
shallow, there is no need to inject or place fertilizer
deep in the soil. However, shallow soil injections
on mounds, berms and slopes, and in compacted
soil will reduce the amount of fertilizer runoff due
to irrigation or rain.
A large, aesthetically-pleasing mulched area
should be maintained around trees and shrubs. A
general rule is to maintain a 2-foot diameter mulch
area for each inch of trunk diameter on newly
planted trees, i.e. a tree with a 2-inch diameter
trunk would grow best with a 4-foot diameter
mulch area. The size of the mulched area can be
increased as plant size increases. This mulched
area promotes faster tree establishment by elimi-
nating grass root competition for water and nutri-
ents. Also, the maintenance of turf areas adjacent
to plant trunks is not recommended because it is
difficult to trim the turf without damaging trunks.
However, other ground covers that are not such
strong competitors for water and nutrients can be
planted near trees.
Fertilizer should be applied to the mulch surface
and to the unmulched area around a tree not to
Associate professor and assistant professor, respectively,
Department of Environmental Horticulture, IFAS, University of
Florida, Gainesville, FL 32611
exceed one and one-half to two times the canopy
diameter (Figure 1). If the turf was fertilized
within the past 2 weeks, do not apply additional
fertilizer to the turf area around the tree; restrict
the fertilizer to the mulched area. The fertilizer
nutrients will move rapidly with the irrigation
water through the mulch.
Most established trees (3 to 5 years after trans-
planting) growing in landscapes where turf and
shrubs are fertilized do not need additional fertil-
izer. Their root systems extend throughout the
landscape past the edge of the tree canopy and
receive nutrients when these areas are fertilized;
however, supplemental applications may be needed
for some trees because nutrient deficiencies could
There are a few situations where trunk injection
of fertilizer is warranted. Each situation is differ-
ent and the merits of injection should be judged by
a professional tree specialist. Remember that trees
are permanently damaged by trunk injections and
the potential benefits must outweigh this damage.
0 apply fertilizer to this area
Figure 1. Fertilizer should be applied on the mulch surface
and around the unmulched surface not to exceed one and one-
half to two times the canopy diameter. If the turf was fertilized
within the past two weeks, do not apply additional fertilizer to
the turf area; restrict the fertilizer to the mulched area around
the tree with the amount of fertilizer applied based on the
mulch square footage.
Trees, shrubs and ground covers can be fertilized
4 to 6 weeks after planting. Most established
landscape plants grow well with two or three
fertilizer applications per year. One application is
normally scheduled around February (south
Florida) or March (north Florida) and another in
September (north) or October (south). The third
application can be made during the summer. Fall
applications facilitate nutrient utilization during
the cool months and are very important for growth
flushes in the spring.
A soil test will provide information about the
nutritional status of a soil and may aid in the
detection of potential problems which could limit
growth. Test the soil area to be fertilized prior to
purchasing fertilizer. Obtain a composite soil
sample by removing subsamples from 10 to 12
small holes dug throughout the sample area (e.g.
the front yard of your home). Carefully pull back
mulch, grass or ground covers to expose bare soil.
With a hand trowel or shovel, dig the small holes 6
inches deep and remove a 1-inch thick by 6-inch
deep slice of soil from the side of each hole. Com-
bine and mix the subsamples in a plastic bucket.
Obtain separate composite samples from areas that
have different soil types, receive different cultural
practices or contain plants that have distinctly
different fertility requirements. Two to three
areas of a 1/4- to 1-acre lot will often be sampled
separately. Soil samples should be sent immedi-
ately to the University of Florida Extension Soil
Testing Laboratory or a commercial laboratory.
Samples sent to the University of Florida should be
accompanied by IFAS form 2811 (Landscape and
Vegetable Garden Soil Test Information Form)
with the appropriate landscape plant option se-
lected. Remember that sample collection should
precede spring fertilization by a couple of months.
A complete fertilizer with a ratio of approxi-
mately 3:1:2 or 3:1:3 (e.g. 15-5-10 or 15-5-15) of
nitrogen (N), phosphorus pentoxide (P20,) and
potassium oxide (K20) is generally recommended
unless the soil test reveals that phosphorus and
potassium are adequate. Fertilizers that are "slow-
release," "controlled release," sulfur coated, or with
nitrogen as IBDU or ureaformaldehyde have
extended release periods compared to fertilizers
that are readily water soluble. Thirty to 50% of the
nitrogen should be water insoluble or slow-release.
This is beneficial because plant roots can absorb
the nitrogen over a long period of time. A fertilizer
containing 30% to 50% slow-release potassium
should be used in south Florida or where soil
potassium is frequently inadequate. A fertilizer
containing magnesium may be needed if plants
often exhibit magnesium deficiency symptoms and
for soils with inadequate magnesium.
Water-soluble fertilizer is less expensive than
products that provide extended release, but the
components of the water-soluble fertilizer may
leach quickly through the soil. In sandy soils, the
soluble fertilizer may move past the root system
after only a few inches of rainfall or irrigation. In
finer-textured marl, clay or muck soils, leaching
will be slower, but runoff may be greater.
Micronutrient deficiencies can be corrected with
foliar sprays if deficiencies are not severe; however,
correction is usually temporary. Persistent defi-
ciencies may be prevented by applying a fertilizer
with micronutrient supplements. Micronutrients
should be applied singularly to the soil only in the
case of severe deficiencies because of the danger of
applying excessive amounts. Maintenance of
recommended pH will minimize micronutrient
deficiencies. Recommendations for raising soil pH
are noted on the soil test report and recommenda-
tions for lowering pH are given in Circular 858,
Selecting and Planting Trees and Shrubs, available
at the County Extension Office.
For each application, apply a maximum of one
pound of nitrogen per 1000 square feet. This rate is
easy to calculate from the information given on the
fertilizer bag. Simply divide the nitrogen percent-
age (the first number of the analysis) into 100.
Example: You have purchased a 15-5-10 fertil-
izer, divide 15 into 100.
Therefore, 6.6 pounds of 15-5-10 will supply one
pound of nitrogen to be distributed over 1000
square feet of landscape area.
VL = VERY LOW
MED = MEDIUM
HI = HIGH
VH = VERY HIGH
Table 1. Target pH and recommended nitrogen, phosphorus pentoxide (P20) and potassium oxide (K 0) fertilizer rates for
ornamentals in the landscape. Phosphorus and potassium rates are based on interpretation of a MehAch-I soil test.
Phosphorus and potassium may not be recom-
mended depending on soil test results (Table 1).
Soils low in phosphorus and potassium should
receive the equivalent of 0.7 and 1.4 pounds of
phosphorus pentoxide (P205) and potassium oxide
(K20), respectively, per 1000 square feet per year.
Phosphorus can be applied in one application;
however, the total amount of potassium should be
divided into three applications per year.
Palms exhibit certain nutritional disorders in
unique ways. A recommended palm fertilizer for
south and central Florida should have 10% to 20%
nitrogen, 5% phosphorus pentoxide, 10% to 20%
potassium oxide, 1% to 3% magnesium and 0.5% of
both manganese and iron. This type of fertilizer is
often referred to as a "palm special." The fertilizer
should also contain sulfur and trace amounts of
zinc, copper and boron. If possible, purchase a
fertilizer which has the nitrogen, potassium and
magnesium in controlled or slow-release forms;
soluble forms of these nutrients must be applied in
small amounts more frequently to prevent leach-
ing. Additional palm fertilization recommendations
are given in the Palm Nutrition Guide by Drs.
Broschat and Meerow of the Ft. Lauderdale Re-
search and Education Center.
Too much nitrogen promotes excessive growth
which increases maintenance costs and time.
Disposing of excess growth as yard wastes is an
additional problem and expense. Application of too
much soluble nitrogen causes environmental
concerns, i.e. nitrogen leaching into water supplies
or polluting surface waters such as lakes, rivers,
bays and retention ponds. Additionally, nitrogen is
not utilized efficiently by unthrifty plants. Dis-
eased or damaged roots, improper soil pH, water-
logged sites and plantings that are too deep can
result in inefficient nutrient absorption and nutri-
ent deficiency symptoms.
1. Gilman, E. F. 1987. Effect of soil compac-
tion and oxygen on vertical and horizontal root
distribution. Journal Environmental Horticul-
2. Gilman, E. F. 1988. Tree root spread in
relation to branch drip line and harvestable root
ball. HortScience 23(2):351-353.
IF SOIL TEST RESULTS INDICATE
NITROGEN PHOSPHORUS PENTOXIDE (P20O) POTASSIUM OXIDE (KO0)
VL LO MED HI VH VL LO MED HI VH
DESCRIPTION pH THEN APPLY (pounds per 1000 square feet per year)
WOODY 6.0 2.3 0.7 0.7 0.4 0 0 1.4 1.4 0.7 0 0
TREES in the
AZALEAS 5.5 1.1 0.3 0.3 0.2 0 0 0.7 0.7 0.3 0 0
IXORA in the
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES,JohnT.Woeste,
director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30 1914 Acts of Congress and is authorized to provide research, educational information and other services only toinividuals and instutions that
function without regard to race, color, sex, age, handicap or national origin. Single copies of extension publications exudingg 4-H and youth
publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers
is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing
this publication, editors should contact this address to determine availability. Printed 6/91.