of Rhode Island GreenShare Factsheets
a Fertility Program for Lawns
a fertility program is one of the most important and complex
a turf manager will have to make. While it would be convenient
to have a generic program that could be applied to all situations,
there is no one program which will produce excellent turf under
all conditions. Fertilizer needs vary according to existing
nutrient levels, species conditions, level of quality desired and
many other factors. Thus, rather than providing a "cookbook" recipe
for success, it is more practical to discuss the components
sound fertility program and then adapt those principles to a particular
situation. The four main variables in any fertility program
nutrient to be applied, frequency of application, rate of application
and timing of applications throughout the season.
addition of fertilizer and liming materials to a lawn should be
based on a soil test. A soil analysis for plant nutrients, texture
and pH is especially important at turf establishment or renovation.
When working with an established, healthy turf, a pH test will generally
following guidelines describe how to sample a turf area for accurate
A separate sample should be submitted for each distinct area of
the lawn where soil properties may differ. Poorly drained areas,
previous gardens, etc. should be sampled separately. An average
lawn will require only one or two samples.
2. Each sample submitted should be a composite of several smaller
samples taken within the area. Six to ten cores taken at a depth
of 6 inches (the root zone) will usually provide a good sample of
the area. A half-pint sample will be sufficient. Thatch and other
debris should be removed from the sample prior to submission.
Contact the University of Rhode Island Cooperative Extension for
information on how to submit soil for a soil test, or see GreenShare
Factsheet on soil testing for an order
form in PDF format.The report for your soil will be sent to you
by mail, along with instructions as to what nutrients to apply and
at what rate. Be sure to specify whether the test is for existing
turf or for an area to be established at a later date.
the 16 essential mineral elements necessary for growth, nitrogen
(N), potassium (K), and phosphorous (P) are the principal nutrients
applied in most fertility programs. Fertilizers which contain
P and K are considered to be "complete fertilizers." Turfgrasses
require N, P and K in a ratio of approximately 4-1-2. When fertilizing
existing turf, it is a good idea to use a fertilizer which provides
N, P and K in roughly this ratio, rather than a fertilizer which
provides more P than K, unless specified by soil test results.
is the backbone of a fertility program and is applied in the greatest
amount because of its many effects on turfgrass growth. Adequate
nitrogen maintains a dark green color, high shoot density and the
ability to recuperate from stress or pest injury. Excessive N,
can increase disease problems, reduce tolerance to high and low
temperature and result in moisture stress due to increased growth
exceeding available moisture. Thus it is important to provide N
at a frequency and rate which will assure vigorous growth without
source of N can be chosen which is either quickly available to the
plant [water soluble nitrogen (WSN)] or slowly available to the
plant over a period of months or even years [water insoluble nitrogen
(WIN)]. Both types of N have advantages and disadvantages. WSN comprises
the majority of N applied by turfgrass managers (Table 1). Of these
fertilizers listed, urea is the most commonly used source of N in
most complete fertilizers. Ammonium nitrate, ammonium sulfate and
potassium nitrate have a higher salt index and are more likely to
burn turf than urea. Mono- and diammonium phosphate are used in
fertilizers when P is also desired.
provides a rapid increase in both color and growth rate. It can
be applied in either granular or liquid form and is less expensive
than the WIN sources. Because the release of N from WSN sources
is relatively independent of temperature, WSN can be used throughout
the season with acceptable response.
to more insoluble N sources (WIN), some disadvantages of WSN include:
high foliar burn potential when applied at excessive rates or during
periods of high temperature, relatively short period of plant response
(six to eight weeks at normal rates) and greater potential for loss
via leaching or volatility (gaseous losses).
insoluble nitrogen (WIN) can also be incorporated into a fertility
program. WIN releases its N slowly over a longer period of time
than WSN. Because of their ability to meter out N slowly over a
long period of time, slow release N sources have a low potential
for foliar burn. They also provide a longer residual plant response
than WSN and do not result in flushes of rapid growth. WIN is less
reactive than WSN so that less is lost via leaching and gaseous
Potential disadvantages associated with WIN include: slow color
response, high cost per unit of N and potential carryover of N into
the following growing season. Carryover of N may or may not be a
problem, depending on the situation. In a low-maintenance situation
where the frequency of fertilizer applications is low, carryover
of nitrogen would be beneficial. Nitrogen would be available for
a longer period to supply nutrients to the slowly growing turf.
For homeowners, inclusion of some WIN in a fertilizer is desirable,
especially on sandy soils prone to leaching.
slow release N sources include: ureaformaldehyde products (UF),
isobutylidene diurea (IBDU), sulfur coated urea (SCU), and products
derived from natural organic materials such as activated sewage
sludge, seaweed and other plant and animal residues (Table 2). Ureaformaldehyde
(UF) fertilizers (38% N) depend upon microbial activity to release
N from complex organic polymers (long chain compounds). Thus, factors
which favor microbial activity also favor N release. Soil temperatures
higher than 55 0F, adequate moisture, adequate aeration and pH between
6.0 and 7.0 allow UF products to work properly.
Coated Urea (SCU, 32-36% N) and plastic or resin-coated urea products
release N slowly because the urea pellet (prill) is covered with
a coating of sulfur, plastic or resin. N leaks through the pores
at a slow rate compared to uncoated urea. Prills which have an incomplete
or cracked coating behave like WSN. Thinly-coated prills release
N more rapidly than thickly-coated prills. Adequate moisture and
warm soil temperatures (warmer than 550F) favor release of N from
SCU and other coated urea fertilizer products. Isobutylidene diurea
(IBDU, 38% N) releases N as a result of very slow solubility in
water. The physical process is essentially similar to dissolving
sugar or some other soluble product, only at a much reduced rate.
Finer particle size products are available for use on low-cut areas
or where a more rapid response is desired. Because they rely upon
moisture for release, IBDU is not a good choice for non-irrigated
turf areas. It is not commonly found as the nitrogen component in
most complete fertilizers. Because its release is not affected by
temperature, it is a good choice for early spring or late fall fertilization
when adequate natural rainfall is usually plentiful.
organic fertilizers vary in composition depending on source of nitrogen
used. The most common natural organic products are derived from
sewage sludge by dewatering, aerobic digestion, composting and/or
further processing or some combination of these techniques. Other
natural organic fertilizers include: seed meal (7% N), fish meal
(7-12% N), pelletized sewage sludge (3-6% N), dried blood (13% N)
and various other composted materials. Because both WSN and WIN
have desirable attributes, it is usually a good idea to use a fertilizer
which contains some of each type. Many commercially available fertilizers
contain both WSN and WIN. The ratio of each in the product vary
according to release rate desired, price and other factors. The
percentage of each type in a fertilizer material is listed on the
Once an N fertilizer has been chosen, one must decide the rate to
apply the product. Fertilization rate depends upon many factors
such as: N source to be applied, time of year and fertility requirement
of the species and cultivars present. When using solely WSN, application
rates of 0.75 to 1.5 lbs. N per 1000 sq. feet per application are
recommended to avoid undesirable growth surges and potential foliar
burn. WIN sources may be applied at rates as high as 3 lbs. N/1000
sq. feet per application without fear of burning the turf (we suggest
going no higher than 2 lbs. N/1000 sq. feet). Fertilization during
July and August should be approached cautiously to avoid excess
growth during periods of high temperature and moisture stress. The
proportion of WIN in a fertilizer is often increased when approaching
the summer or during the summer to protect against foliar burn.
Fertilization programs utilizing only WSN require more frequent
applications to maintain acceptable turf than programs which incorporate
some WIN. Fertilization programs can include up to five applications
to a lawn per season with three or four of those applications containing
N fertilizer. The timing of those fertilizer applications during
the season is an important consideration.
agronomists consider late summer (August/early September) and late
fall (late November, when the turf has gone dormant) fertilizations
to be the most important for cool-season grasses. Recovery from
summer stress injury, as well as increased tillering and rhizome
production, occur during the fall. N must be provided to maximize
these processes. The late fall application should be made after
the last mowing when turf has stopped growing, but before it has
lost its green color. An application at this time enhances winter
color and provides spring greenup three to four weeks earlier than
programs without a late-season application. This concept has also
been shown to improve Kentucky bluegrass rooting the following spring.
While late season fertilization is increasing in popularity, it
must be approached cautiously. In areas which may be environmentally
sensitive, late-season fertilizing should be avoided.
N application during late spring is also widely practiced in order
to enhance color going into summer and to encourage growth before
the high temperatures and moisture stress of summer occur. It is
important that this application does not stimulate the turf to rapid
growth during the stressful summer months (especially if irrigation
is not available). Fertilizer applied at this time should contain
a high percentage of slow-release or water-insoluble nitrogen. Many
programs also employ an early spring (April) application of N. This
application is used primarily to enhance greenup at the time when
preemergent weed materials are being applied. If a late-season application
is used, the N rate during early spring can be reduced substantially,
since color will be markedly enhanced from the late season application.
Iron applied without nitrogen at this time of year also enhances
color development without stimulating growth.
N is the main component of all fertility programs, several other
elements also bear mention. Potassium (K) is needed by turf in amounts
second only to N. Adequate K fertility improves wear tolerance,
heat and cold tolerance, stolon and rhizome growth and rooting (improving
water uptake). While every fertilizer application may not include
K, those applications preceding stress periods are good times to
supplement K. The early fall application, in particular, is often
made with a fertilizer containing N and K in a 1:1 ratio to improve
winter survival without overstimulating growth.
(P) improves both rooting and winter hardiness of turf. It is essential
when establishing new seedings of turf. Adequate P in the seedbed
helps to ensure rapid establishment. On mature turf, where P is
rarely found to be deficient, there is little value to applying
P unless a soil test shows it to be deficient. P is strongly bound
to the soil and does not easily move downward. It is a good idea
to apply P in conjunction with some process which will facilitate
its incorporation into the soil (aeration, dethatching, etc.).
element which can be incorporated into a fertility program
(Fe). Iron, which functions in chlorophyll synthesis, provides
a rapid increase in green color when growth stimulation associated
with N is undesirable. Early spring or summer applications
are becoming increasingly popular. Iron is very strongly absorbed
to the soil, making it often unavailable to the plant for use.
order to increase plant availability, iron is applied as a liquid
rather than as a granular product. "Chelated" iron is often
chosen as a source of Fe. A chelating agent is a soluble organic
that binds with Fe to make it more available to the plant. Intelligent
use of Fe can result in a healthier plant and reduced need
A typical fertilization program results in the application of about
2 to 4 lbs. N per 1000 sq. feet per season. The main objective is
to produce acceptable quality turf. If you are satisfied and the
turf is healthy at a rate lower than 3 lbs. N per 1000 sq. feet
per season, reducing the rate is justified. A material containing
both WSN and WIN provides some of the advantages of WSN (quick greenup,
release independent of temperature and lower cost than WIN) while
incorporating some advantages if WIN (lower burn potential, less
leaching and less frequent application than WSN). There are many
factors which must be taken into consideration when formulating
a fertility program. A basic knowledge of plant nutrition, fertilizers
and soils, as well as a willingness to experiment with your current
program, are keys to finding the program best suited to your situation.
from the University of Massachusetts Extension, 2000
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program