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Copyright 2005, Board of Trustees, University
FERTILIZER FACTS FOR FOLIAGE GROWERS '4
Charles A. Conover
University of Florida, IFAS
Apopka, FL 32703 '.
ARC-Apopka Research Report RH-78-2
So many types of fertilizer are available to foliage growers- that
selection of a particular source, ratio and analyses is difficult. Of
particular importance to producers are (1) does the fertilizer source
grow good plants, (2) is the fertilizer source efficient, i.e., is use
of all or most of the active ingredients such as nitrogen obtained, and
(3) is the fertilizer source economical in cost per unit of fertilizer,
labor required for application and capital investment in equipment.
None of the presently available fertilizers rate highest in all
categories listed above. Additionally, temperature, rainfall, potting
medium and crop production cycle should all influence selection of a
fertilizer source. Thus, selection of a particular fertilizer depends
on factors listed below:
Results obtained from various fertilizer sources
Nearly 8 years of research on foliage plants with numerous fertilizer
sources has shown that many are acceptable, but that several are more
efficient in terms of growth and quality. Comparisons between fertilizer
sources should only be made when nitrogen is applied at similar levels,
although differences in levels of other nutrients should be considered.
Plant response depends on availability of nutrients as well as the period
of release for slow release sources. Table 1 provides an indication of
fertilizer efficiency for sources used at this research center. As shown
in the table, 1.33 pounds of a Urea Formaldehyde based fertilizer is
needed to get the same response as 1 pound of a liquid fertilizer of the
same analysis. Some of the reasons for this are that not all of the
nutrients may be released from slow release sources during the crop
cycle, and also, as foliage plants normally grow rapidly they require
nutrients be readily available as needed, which may not occur with some
slow release sources.
Table 1. Relative efficiency of several fertilizer sources based on foliage
plant response observed under experimental conditions.
Frequency of Relative* Lbs needed for
Fertilizer source application efficiency equal response
Liquid Weekly 100 '1.00
Dry (100% water soluble) Weekly 100 1.00
Slow release (Osmocote) Every 3 months 90 1.13
Slow release (Sulphur coated) Every 3 months 90 1.13
Slow release (Urea Formaldehyde) Every 3 months 75 1.33
Plant response to liquid fertilizer has been higher than other sources and has
been assigned a relative efficiency of 100 however, actual efficiency would
Fertilizer ratios (Nitrogen:Phosphorus:Potassium) are important, but,
experimentally, we have not noticed any difference between ratios of 1:1:1,
2:1:1 or 3:1:1. However, use of potassium at less than 50% or phosphorus
at less than 75% of the nitrogen level is not recommended, as deficiencies
Actual cost of fertilizers varies considerably even within a local area.
Prices listed in Table 2 are for 1 ton lots purchased from standard supply
sources in January, 1978.
Table 2. Approximate fertilizer cost per ton and/lb N for several fertilizer
Fertilizer source Manufacturer Cost/ton Cost/lb Nitrogen
9-3-6* USS Agri. Chem. $134.75 $ .75
16-4-8* USS Agri. Chem. 195.90 .61
Dry (100% soluble)
20-20-20* Peters 827.20 2.07
20-2-20 Mixed from NH4NO3, HPO4
and KNO3 216.80 .54
Slow Release (Osmocote)
19-6-12 Sierra Chem. Co. 879.90 2.32
18-6-12 Sierra Chem. Co. 916.65 2.55
Slow Release (Sulphur Coated)
14-14-14* Atlantic Fert. Co. 540.00 1.93
14-14-12* Nurseryman's Sure Gro Corp. 602.00 2.15
Slow Release (Urea Formaldehyde)
25-10-10 Scott's 640.00 1.28
18-6-12 Atlantic Fert. Co. 560.00 1.56
It is easy to change the fertilizer cost to reflect price changes in your
area and to obtain costs associated with your type of operation. When
calculating fertilizer costs, one must consider not only cost per ton, but
also cost per unit of fertilizer as well as associated equipment and labor
costs of application.
A quick reference to several commonly used fertilizer sources and
their approximate costs is listed in Table 3.
Table 3. Fertilizer costs ($) when 1500 lb N/A/yr is obtained from several
sources and applied broadcast or placed within containers*.
Cost/1000 ft2 (1000 6" pots)
Fertilizer source Manufacturer Broadcast 6" O.C.
9-3-6** USS Agri. Chem. $ 43.27 $ 8.49
16-4-8** USS Agri. Chem. 38.45 7.55
Dry (100% soluble)
20-20-20** Peters 98.37 19.30
20-2-20 Mixed from NH4NO3, HPO4 51.65 10.14
Slow Release (Osmocote)
19-6-12 Sierra Chem. Co. 99.36 19.50
18-6-12 Sierra Chem. Co. 108.32 21.26
Slow Release (Sulphur Coated)
14-14-14** Atlantic Fert. Co. 84.19 16.52
14-14-12** Nurseryman's Sure Gro Corp. 92.75 18.20
Slow Release (Urea Formaldehyde)
25-10-10 Scott's 67.71 13.29
18-6-12 Atlantic Fert. Co. 80.54 15.81
Includes materials, equipment and labor.
The economic data in Table 3 are self-explanatory. However, several
comments can be made:
1. Broadcast application of liquid or dry soluble fertilizers is
much more expensive than in pot application. In addition,
when either is applied broadcast, the actual amount of fertilizer
being applied to the potting medium surface of container-grown
plants can vary because of deflection by the plant canopy. This
deflection may be as high as 50% with some types of plants.
Another problem with broadcast application is the large amount
of fertilizer that falls between the pots and runs off. New
fertilizer containment requirements by EPA will someday prevent
this application method.
2. Direct container applications of several liquid or soluble
fertilizers are lower in cost than most slow releaseforms
placed in the container. However, a quick inspection of
Table 3 will show that this is not always true, since pre-
mixed soluble fertilizer can be as expensive as other sources.
3. Cost consideration has not been given to inclusion of micro-
nutrients in the fertilizer program. The problem is that just
because a fertilizer source contains micronutrients they may
not be present in the proper ratio or quantity. Several
fertilizer sources listed that do contain some micronutrients
also require the addition of others or inclusion of another
micronutrient supplement in-the potting medium. Lack of
micronutrients or the need to supply additional ones will
add approximately 10% to the total fertilizer cost.
Selection of fertilizer sources
Selection of a fertilizer source depends on several factors in addition
to cost and application systems, and some of those that need to be considered
for listed sources follow:
Liquid Best plant growth usually occurs when liquid fertilizer is applied
to pots on a weekly or every 2 weeks basis, or in a constant feed program.
However, monthly application is often acceptable under greenhouse cover.
Where plants are subject to rainfall, especially during summer when rapid
growth occurs, monthly applications will not be adequate. Stock benches and
beds can be fertilized on a monthly basis without significant loss of'yield.
Be careful when selecting a liquid fertilizer, as some may clog spagetti tube
watering systems. Remember, liquid sources are fast acting and available to
the plant within hours of application. They can be leached from the potting
mixture, but their availability is not limited by temperature or soil micro-
Dry (100% soluble) Basically the same as liquid fertilizer; since it is mixed
with water to form liquid fertilizer. Be sure that all components go into
solution, since this may effect the ratio and analyses if they do not. Also,
suspended solids may lodge in injectors or spagetti tube watering systems if
all fertilizer does not go into solution.
Slow Release (Osmocote) This source releases through osmotic action (a
concentration gradient forms between the potting mixture and the capsule).
However, this can be strongly influenced by temperature. The release curve
is good at a 700F soil temperature, but at 80 or 90F soil temperature it
is often extremely rapid. During periods of extremely high temperature, it
may be better to apply a lesser amount more frequently. Reduced release rate
during cool weather is less important, since plants will not be actively
growing then. As all ingredients are coated, this is truely a slow release
fertilizer. For this reason, it cannot be leached from the potting mixture,
and thus applications should be timed to the production cycle so that large
amounts of fertilizer are not present at time of sale.
Slow Release (Sulphur Coated) Although called a slow release fertilizer
by many, this is not entirely true, since only nitrogen is in a slow release
form. The remaining elements are immediately available and may cause damage
if a high rate is utilized. Nitrogen is released when it goes into solution
and leaches slowly through the sulphur coating. The process of coating urea
with sulphur is somewhat inexact and thus the release rate sometimes varies
between lots. Another problem is possible growth reductions near the end of
the application cycle, since most of the phosphorus or potassium may be con-
sumed or leached.
Slow Release (Urea Formaldehyde) Although often termed a slow release
fertilizer, this is not entirely true, since only nitrogen is in a slow
release form. The remaining elements are immediately available, and may
cause damage if a high rate is used. The nitrogen from Urea Formeldehyde
is made available to plants by the action of microorganisms, as most of
the compound is insoluble in water. Therefore, release is slow when few
microorganisms are present such as with sterilized soils. Since a
significant portion is not available for up to a year, it is necessary
to supply plants higher than recommended rates to get the desired response.
Because of the very slow release characteristic, plant growth is sometimes
slowed during periods when rapid growth could be occurring, because the
release rate is less than plant demand.
This public document was promulgated at an annual cost of $25.97 or
5.2 cents per copy to inform county and state extension personnel,
Foliage growers, marketers and allied trades of research results
and improved practices in ornamental horticulture.