GRASS CLIPPING FOR COMPOSTING
increased, and some landfills no longer accept
grass clippings, many individuals and governmental agencies are seeking alternatives for disposal of
clippings. During the maximum grass growing
period, the municipal refuse load in some New
Jersey suburban communities may contain nearly
one-third grass clippings. Collected clippings
become anaerobic very quickly because of their
high demand for oxygen. After becoming anaerobic they emit strongly unpleasant odors. Therefore, grass clippings (in quantity) are difficult to
handle and to process.
From our own experience with the handling
and disposal of grass clippings, and discussions
with others such as lawn care professionals, we
suggest considering the following methods to
reduce landfilling:
1. RETURN TO LAWN — It is most desirable to leave grass clippings uncollected on the
lawn so that they are recycled, contributing to soil
organic matter and supplying part of the fertilizer
needs of the lawn. Adopt a mowing schedule to
keep clippings short enough to filter through
growing grass and not remain as a mat on top of
the lawn. Research and experience indicate that
only 1/3 of the grass length should be removed
during mowing. Never allow the lawn grass to
double its height between mowings. This approach
not only eliminates clipping collection and disposal
problems, but also can contribute to improvement
of the lawn.
Clippings are not a cause of thatch in lawns.
Rather, thatch is formed primarily from a dense
accumulation of grass roots and stemmy material.
Returning clippings along with proper mowing
frequency will not increase disease problems.
Use caution when removing collection bags
from mowers. Some machines are not designed to
operate safely without a bag or other attachment in
place. If you are unsure, check with your equipment supplier.
2. GARDEN MULCH — Grass clippings can
be used as a garden mulch. To minimize any
tendency to protect slugs, clippings can be dried in
the sun for a day prior to being used in this way.
Clippings can be spread on garden soil to check
weed growth, reduce soil spattering and crusting,
moderate soil temperatures, etc. As a precaution,
do not use grass clippings from herbicide-treated
lawns until after two grass cuttings have been
made.
3. SOIL INCORPORATION — Clippings
can serve as a source of organic matter for soil
improvement when incorporated into the garden.
4. BACKYARD COMPOSTING — Grass
clippings can be composted, particularly when
incorporated into a backyard leaf composting pile.
However, grass has a high nitrogen content, a
much higher demand for oxygen than leaves, and a
tendency to mat, thereby greatly reducing the
passage of oxygen. Composting piles containing
grass clippings thus readily become anaerobic.
This, in turn, can produce strong, unpleasant odors.
These odors are particularly noticeable when the
pile is disturbed.
Because of these problems, grass clippings
should not be composted alone, but rather mixed
with composting leaves. The partially decayed
leaves which now (6-9 months after leaf fall) have
a low demand for oxygen, will serve as a bulking
agent permitting more oxygen to reach the grass.
Grass, which is high in nitrogen, will provide a
more rapid decomposition of the remaining leaves
as long as it remains under aerobic conditions.
Grass clippings will also contribute to a better end
product (higher nitrogen content) than that obtained from composting leaves alone. One must be
aware, however, that an excess of damp grass in
the pile will soon become anaerobic, produce very
unpleasant odors, and reduce the rate of decomposition. The objective is to keep the material
aerobic. Also, to ensure that excess nitrogen is not
given off as ammonia, do not add more than 1 part
fresh grass clippings to 3 parts partially composted
leaves.
The resulting compost can be used as a soil
amendment, as a mulch for gardens, flower or
shrub beds, or as a potting medium.
5. MUNICIPAL COMPOSTING — Some
grass clippings can be incorporated into a municipal leaf composting operation. However, problems
that may be experienced with backyard grass
composting could be greatly magnified at a municipal facility. Even grass stored for one day or
less in plastic bags or the back of a lawn maintenance pick-up truck may emit very unpleasant
odors when being unloaded at the site. For this
reason, grass clippings are banned at many leaf
composting facilities, unless they are very isolated.
Research is continuing in this area, but other
problems include the high cost of collection and an
inadequate supply of leaves for the amount of
clippings.
Partially composted leaves should be mixed
with the grass in a 3:1 ratio, or more. Because the
leaves have already decomposed by the time the
grass comes to the site, however, this means the
ratio actually collected must be at least 6:1. For
most towns this would be possible only if most of
the grass clippings are handled directly by residents
on their own property.
6. CLIPPING REDUCTION — Fertilizing
and watering above the requirements of the grasses
may be more detrimental than beneficial to the
lawn. One of the effects is increased production of
clippings. (Another is potential ground or surface
water pollution.) Judicious and proper use of
fertilizer and water can provide an attractive lawn
with a reduction in the costs, effort, susceptibility
to disease, and amount of clippings produced. A
fertilization program should emphasize fertilizing
the lawn in the fall season rather than in the spring.
This can be effective not only in reducing the
amount of clippings produced, but also in contributing to a better lawn.
Two related fact sheets: “Backyard Leaf
Composting” (FS074) and “Using Leaf Compost”
(FS117), and assistance with procedures covered
above, may be obtained from the Rutgers Cooperative Extension office in your county. The telephone number appears under County Government
in your local phone directory.
Peter F. Strom, Ph.D., Associate Professor of Environmental Science; James A. Murphy, Ph.D., Extension Specialist in
Turfgrass Management; and Henry W. Indyk, Ph.D., Extension Specialist Emeritus in Turfgrass Management
(http://ce-drupal01.rutgers.edu)
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