Environmental Management Council
What is composting?
Composting occurs nearly
everywhere! Leaves drop from trees. Grass clippings are left after mowing the lawn. Plants and
animals die. These are some examples of organic materials which, over time, break
down or decompose. The rich, dark, soillike material that results is called compost.
Composting takes place when tiny
living things, called microorganisms, work to break down organic material. Microorganisms
include such things as bacteria and fungi. Animals living in the soil help
microorganisms break down organic materials. Worms and pill bugs are examples of soil animals
that help change organic wastes into compost.
As microorganisms and soil animals
turn organic materials into compost, they use it as food. The organic materials provide
nutrients for growth and activity. Eventually, these nutrients are returned to the soil,
to be used again by trees, grass, and other plants. This is nature’s way of composting
Dutchess County Environmental
AFFECTING THE COMPOSTING
All natural organic material
eventually decomposes. The length of the
composting process depends on
a number of factors:
♦ Carbon and nitrogen contents of the
♦ Amount of surface area exposed
♦ Temperatures reached during
When combining materials to make
compost, its important to understand the carbonto-nitrogen (C:N) ratio of organic wastes.
Simply, all organic materials are made up of the element carbon and may also contain
some percentage of the element nitrogen.
Composting microorganisms and soil animals digest carbon for energy and
ingest nitrogen for
reproduction. Given a proper balance of carbon to nitrogen, microorganisms can decompose compost piles
quickly. The ideal C:N ratio for composting is 30 parts carbon to one part
nitrogen (30:1). Table 1 lists carbon-tonitrogen ratios for materials commonly included in
Most materials available for composting do not fit this ideal 30:1
ratio, so different materials
must be blended to create a fast decomposing pile. In general, coarse, dried-out material contains very little
nitrogen. For example, oak leaves and wood chips are high in carbon and decompose
slowly. Grass clippings have a low C:N ratio and decompose quickly. The presence
of nitrogen in compost piles ensures that temperatures will be high enough for the
process to work efficiently and that decomposer organisms have a nutrient
source for reproduction.
SIMPLER TERMS, ORGANIC WASTES WITH HIGH C:N RATIOS ARE
WASTES WITH LOW C:N RATIOS ARE “GREENS.”
Although proper blending of
“Browns” to “Greens” is necessary, it can be difficult to blend materials to achieve this ratio
exactly. For example, the C:N ratio data included in Table 1 were calculated on a dry-weight
basis. An estimation of the dry weight and the C:N ratio requires knowledge of the
moisture content of the materials being used. Home composters seldom have the equipment,
or the inclination, to measure moisture contents. Also, the C:N ratios in Table 1
are only estimates. For instance, brown grass clippings from a dry lawn will have
less nitrogen than lush, green clippings. Clippings from lawns that have been
abundantly fertilized will have even higher nitrogen content.
OF MATERIALS TO ACHIEVE A WORKING COMPOST PILE IS THE ART OF
WITH CREATIVITY AND CARE, HOME COMPOSTERS WILL DEVELOP THEIR
METHODS THAT RESULT IN GOOD MIXTURES FOR COMPOSTING!
CARBON TO NITROGEN
RATIOS FOR SELECTED
MATERIALS (BY WEIGHT)
|GREENS (High Nitrogen)
manure with litter
manure (with litter)
|BROWNS (High Carbon)
chips and sawdust
Bacteria work to decompose waste at
the surface of each particle in the compost pile. The surface area of material to be
composted can be increased by breaking it into smaller pieces, or by other means. An increased amount of surface
area allows the microorganisms
to digest more material, multiply faster, and generate more heat. Although it is not essential to break
materials into small pieces for composting, it does accelerate the process. This may be
important when space is limited. Materials can be chopped, shredded, split, or
bruised to increase their
surface areas. A wide range of shredders and chippers is available,
large models used by tree services to
small, handcranked types. For
yard wastes, cutting materials
with pruning shears or with a hatchet on a
piece of plywood is adequate.
Even some pounding with a
entry points for decomposer
organisms. An easy way
fallen leaves is to mow them
before raking. The shredded
leaves can then
be collected directly with a
Aeration allows fresh air to
circulate throughout the
pile. Rapid aerobic
only occur in the presence of sufficient oxygen. Aeration occurs naturally when air
warmed by the compost process rises through the pile, drawing in fresh air
from the surroundings. Wind also stimulates aeration. Porosity and moisture content
affect air movement through the compost pile.
Porosity refers to the spaces between particles in the compost pile, or
basically the surface area
contained within the pile. If the material is not saturated with water,
these spaces are partially
filled with air that can supply oxygen to decomposers and provide a path for air circulation. As the
material becomes water saturated, the space available for air decreases.
Compacting the compost pile
reduces its porosity. Excessive shredding can also impede air circulation by creating smaller
particles and pores. Adding coarse materials, such as
leaves, straw, or cornstalks, can increase the pile porosity, although some
coarse materials will be slow to decompose. As the compost
process proceeds, the
porosity decreases, restricting aeration. Regular mixing of the pile,
referred to as turning,
fluffs up the material and increases its porosity. Turning enhances
aeration in a compost pile.
For home composting, turning is easily done using a pitchfork or shovel.
Decomposer organisms work best in
piles that contain the proper amount of moisture. The “squeeze”
test is an easy way to gauge the moisture content of composting materials. The
material should feel damp to the touch, with just a drop or two of
expelled when the material is
tightly squeezed in the hand. If the pile becomes too wet, it should be turned and restacked.
This allows air to circulate back into the pile and loosens the materials for better
draining and air-drying. Adding dry material, such
as straw or sawdust, can also remedy
an excess moisture problem.
If the pile is too dry, it can be watered with a trickling hose. A more
effective practice is to turn
the pile and rewet materials in the process. Certain materials will
shed water or adsorb it only
on their surface. Materials, such as, dead leaves, sawdust, hay, straw,
dried weeds, and vegetables
gradually be moistened until they glisten. Then the squeeze test should be used to evaluate
the moisture content.
A moisture content of 40-60 percent provides adequate moisture without
limiting aeration. If the
moisture content falls below 40%, the bacteria will slow down and may become dormant. When the moisture content
exceeds 60%, nutrients are leached (lost), air volume is reduced, odors are
produced, and decomposition is slowed.
As the microorganisms digest and
multiply they will generate heat, which will increase the temperature of the compost pile. Pile
temperatures between 90°F and 140°F (32° –60°C) are desirable, and indicate rapid
composting. Temperatures greater than 140°F (60°C) reduce the activity of many of the most
Some compostors decide to monitor the temperature of the compost heap.
A temperature probe or a soil
thermometer can be used to
keep track of
pile temperatures. While home
may not be interested in
monitoring pile temperature,
a temperature probe is
for demonstration and useful for
serious composters. Although
this method is
not necessary, it is helpful
as to ways to control the
For instance, a drop
in temperature after
a peak may indicate the need
to turn the
pile to invigorate microbes
with air and a
new food source.
This section discusses materials,
construction, maintenance, and troubleshooting for a compost pile. These principles can be
applied to the turning units, holding units, and heaps that were defined in the
previous chapter. Turning a compost pile regularly can yield compost in one to two
months with the right combination of materials and moisture content. Without turning,
decomposition takes six months to two years. Excellent quality compost can be made
either way. When selecting a composting method, consider volume of organic
waste produced around the home and yard, need for finished compost, and your time
available for maintenance.
and Maintaining a Compost Pile
Almost all natural, organic material
will compost, but not everything
belongs in the compost pile. Some
wastes attract pests; others
contain pathogens that can survive
the compost process, even if
the pile gets hot. Table 2 divides
materials according to whether or
not they cause these types of
MATERIALS THAT SHOULD AND
SHOULD NOT BE IN A COMPOST
peels and rinds
To avoid problems with odors,
neighborhood animals, and other pests do not compost fatty food wastes, such as meat or bones.
To break down properly, animal fats must be composted at high temperatures over an
extended period of time. Never add cat and dog manure as it can contain
harmful pathogens that are not always killed by the heat of composting. Manure may also
attract cats and dogs to the pile.
Plants harboring diseases, or
suffering severe insect infestations, should not be added to the compost pile. Certain damaging
weeds, including morning glories, buttercups, and some grasses with complex root systems
(such as quack grass), may not be killed if the pile does not heat up. Piles
containing these types of weeds must be turned to encourage the high pile temperatures that
will kill them.
Another consideration in choosing materials to go into the compost pile
is the time they need to
break down. Woody materials, such as wood chips, branches, and paper,
may take up to two years to
break down unless they are finely chipped or shredded. Their high C:N ratios indicate that they require
a lot of nitrogen to decompose, so they may slow the decomposition of other materials
existing in the compost heap. Other materials that break down slowly include;
corn cobs, husks, and stalks, sawdust, straw, apple pomace, and some nutshells. These
materials should be cut into small pieces to increase their surface areas and mixed
with “Greens” like fresh grass clippings.
DOWN SLOWLY SHOULD BE MIXED WITH PLENTY OF “GREENS” TO
COOKING. IF A GOOD SOURCE OF “GREENS” IS NOT AVAILABLE, HIGH C:N
SHOULD BE USED AS MULCHES.
While materials such as wood
chips and straw break down slowly, they also are bulking agents that improve the pile
structure, allowing air circulation. When composting dense, high-nitrogen materials,
such as manure, the addition of a bulking agent may be required to facilitate the
The art of composting is
discovering the mix of materials that will provide the best environment for the compost process.
Mixing materials of different sizes and textures helps to provide a healthy and
well-drained compost pile. Diverse material also helps maintain the right balance of
organics for rapid decomposition.
In communities where residents pay
for garbage disposal by the bag, composting your kitchen scraps, along with recycling of
bottles and cans, is a way to save money on disposal. However, care must be taken when home
composting kitchen scraps, especially
on small lots where pest or odor problems can offend your neighbors.
For best results do the
ONLY COMPOST FRUIT, VEGETABLE, BREAD OR GRAIN WASTES AS THESE ITEMS BREAKDOWN
ALWAYS BLANKET OR COVER FOOD WASTES AMONG AN EQUAL AMOUNT OF “BROWNS” OR
WORKING COMPOST. THIS IS ESPECIALLY IMPORTANT WHEN STARTING A NEW PILE
AS IT WILL HELP HIDE THE SMELL OF “FRESH FOOD” FROM NEIGHBORHOOD ANIMALS.
NEVER LEAVE FOOD WASTE UNCOVERED ON TOP OF YOUR COMPOST PILE, AS THIS WILL
ONLY ENCOURAGE PESTS BY GIVING THEM A CONVENIENT MEAL.
• FOR SMALL YARDS,
CONSIDER AN “ENCLOSED” COMPOST UNIT.
Sod can be
incorporated into a compost
pile; it can also be composted in a holding system with or without a structure. Large
quantities of fresh, stripped sod should be piled with the roots up and grass down, to
keep the roots from continuing to grow.
The sod should then be wetted
thoroughly and covered with a tarp, to keep light out. A large pile of sod may take one to three
years to decompose completely. Small quantities of sod will decompose more
quickly if broken into small pieces.
Grass Clippings Sprayed with Pesticides
Some gardeners are concerned about
composting grass clippings that have been treated with pesticides. Table 3 lists the
persistence of some common lawn herbicides in soil. Composting, as an
accelerated decomposition process, biodegrades many compounds faster that
soil degradation. If yard waste has been composted at least one year, pesticide
residues should not be a problem when the compost is used.
PERSISTENCE OF SOME
COMMON PESTICIDES IN SOIL
Source: Rosen, et.
Inoculants, activators, and lime are
compost pile additives. Inoculants are dormant microorganisms; activators contain sugar
or a nitrogen source, such as ammonium sulfate; and lime increases compost pile
pH. Inoculants are rarely needed, since
earth, leaves, kitchen scraps, and
finished compost already contain ample bacteria that can work readily on their own. Other
nutrients added through the application of organic or chemical fertilizers will have
little effect on the composting process. Table
4 lists estimated amounts of
particular nitrogen sources that should be added to high C:N ratio materials.
THE ONLY ACTIVATOR THAT
MAY BE NEEDED IS A NITROGEN SOURCE, SINCE
USUALLY THE LIMITING NUTRIENT. NITROGEN ACCELERATES
THE MATERIALS TO BE COMPOSTED DO NOT INCLUDE A MATERIAL
WITH A LOW C:N
RATIO, SUCH AS GRASS CLIPPINGS (SEE TABLE 1).
AMOUNTS OF VARIOUS
NITROGEN SOURCES NEEDED TO
APPLY 0.15 POUNDS
(2.4 Ounce) NITROGEN
During the initial stages of
decomposition, the compost pile produces organic acids and the pH may drop. However, since
composting organisms perform best at a pH between 4.2 and 7.2, it is best not to add
lime to adjust pH. Adding lime converts ammonium nitrogen to ammonia gas,
creating an odor problem. As the compost matures, pH will rise, typically to
between 6.0 and 8.0 for finished compost.
|Ounces to Apply
A good location is helpful for a
successful compost pile. Direct sunlight in the summer dries the pile. Exposure to high winds can
dry and cool the pile, slowing the decomposition process. The pile location
should not interfere with lawn and garden activities. Water should be readily
available. There should also be enough space for temporary storage of organic wastes. Good
drainage is important; otherwise, standing water could impede the decomposition
process. The compost pile should not be located against wooden buildings or trees;
wood in contact with compost may decay.
A pile should be large enough to hold
heat and small enough to admit air to its center. As a rule of thumb, the minimum dimensions
of a pile should be 3 feet x 3 feet x 3 feet (1cubic yard) to hold heat. The maximum
dimension to allow air to the center of the pile is 5 feet x 5 feet x any length.
If space is a limiting factor,
the pile sides should be insulated so that the higher temperatures can be maintained in a much
smaller volume. Smaller, commercially available units can be insulated with foam
board. Piles larger that 5 feet tall and wide may need to be turned to prevent
their centers from becoming anaerobic. As the material decomposes, the pile will become
smaller. A yardstick can be used to keep track of, or demonstrate, volume reduction.
Compost piles can be constructed by
adding stockpiled material in batches or by placing materials in the piles as they
become available. The batch method accelerates the composting process if the combined
materials have the right C:N ratio and if the materials are mixed. Guidelines for
constructing a compost pile are given in Section 3.
Maintenance of the compost pile
involves turning the pile and adding water to maintain conditions conducive to the composting
process. If the pile is not turned, decomposition will occur, but at a slower
following maintenance procedure will yield
compost in the shortest time.
In a pile constructed
according to the method described in Section
3 the pile temperature
will increase rapidly and soon reach about 110oF. After about a week, check to see if the pile is warm. If not
try adding more “Greens.” Once the pile has heated, it should be turned to aerate and
any compacted material should be loosened. Then the pile should be reconstructed;
material previously on the top and sides of the pile should be moved to the center to
provide microorganisms fresh food. The pile should then reheat as the
re-energized microorganisms digest wastes and reproduce.
At the second turning (after
about another week), the material should be a uniform coffee-brown color and moist. The
relatively undecomposed outer layer can be scraped off and turned back in to the
center of the pile. The center material should be spread over the outer layer of the
reconstructed pile. By the third turning, the moisture content should be checked using the
squeeze test described earlier. Water should be added, if necessary.
carbohydrates (“Browns”) and proteins (“Greens”) provide most of the
energy for the initial, rapid stages of
decomposition. When the more resistant materials, such as lignin and cellulose (found in plant
tissues), become the main food sources, the activity in the pile will slow down. Less
heat will be produced, and the temperature falls, the compost will continue to
If temperatures are monitored,
use this as a method of compost pile management. If temperatures surpass 140°F, the pile should be turned to cool it
off. Extremely high temperatures
can kill many beneficial organisms. If the pile does not reach at least
120°F, more nitrogen or water may be needed.
Cold weather can also prevent the pile from heating. Piles that give off
strong ammonia smells contain too much nitrogen, and may need more high-carbon
The compost will be finished
when the pile cools off and decreases to about one-third of its original volume (depending on the
original ingredients). It will be dark, crumbly, and have an earthy odor. The temperature
usually will be within 10°F of ambient air temperature. Unfinished compost can
be “phototoxic”, meaning that it introduces toxic material into the plant, and results in
death or impairment of the plant. This phototoxicity occurs especially to
seedlings and newly established plants. Therefore, compost must be allowed to decompose
thoroughly before use.
COMPOST JUST HAPPENS.
LOW-INPUT AND SLOW COMPOSTING PILE MAY
SUIT YOUR NEEDS.
Given a comfortable, or even
nourishing environment, rodents and other
animals may be attracted to
compost piles. The chances of
this are greatly
when piles are maintained, are
actively composting, and the
surrounding area kept clean. Using
some type of enclosed
unit may help the ”low-input
composter” on all these
In urban areas, raccoons and
rats are probably the most undesirable pests. In a hospitable environment with plenty of
food, they can multiply very quickly and can become disease transmitters. Therefore, it
is crucial to keep high-protein and fatty food wastes out of the compost pile in
areas where pests may be a problem. Meat and fish scraps, bones, cheeses, butter,
and other dairy products should be excluded. Remember though, any free source of food
wastes can attract pests.
Many flies, including
houseflies, can spend their larval phase as maggots in compost piles. To control their numbers, kitchen
scraps must be covered with finished compost or an equal amount of “Browns.”
See the previous section on Food Waste for more tips on avoiding pests.
The solutions to most compost
problems are often fairly simple. (The COMPOST TROUBLESHOOTING
GUIDE at the bottom of this web page
explains how to trouble shoot common compost problems.)
for Constructing a Compost Pile
♦ Collect enough
material to create a 1-cubic-yard pile. The material should be the right proportion to approximate a 30:1
♦ Chop or shred any coarse
materials to increase their surface area.
♦ Start the pile with a 4- to
6-inch layer of “Browns” (high C:N ratio materials).
♦ Add a 4- to 6-inch
layer of “Greens” (low C:N ratio materials). Add additional nitrogen if needed. Possible nitrogen
sources were discussed in the “Additives” section of Section 2. Manure is another
source of nitrogen.
♦ Vegetative kitchen wastes
should be added in this layer. If very low C:N ratio materials, such as grass clippings, are
used, layers less than 4 inches thick may be appropriate.
♦ If food wastes are added, an
additional thin layer of soil, sawdust, leaves, straw, or compost should be added to absorb odors.
♦ Consider the porosity
of the mixture. If dense materials, such as manure or wet leaves,
are used, wood chips,
straw, or other dry, bulky material should be added to improve the
porosity. The thickness of the layers will depend on the C:N ratio of the
materials being used.
♦ Mix the layers.
♦ Conduct a squeeze test
to gauge the moisture content of the compost.
♦ Add water until squeezing a
handful will yield one or two drops of water. Adding too much water may leach out nutrients.
♦ Continue alternating
and mixing until the pile is 3 or 4 feet high.
Compost can enrich flower and
vegetable gardens and improve soil around trees and shrubs. It can also be used as a soil
amendment for houseplants and planter boxes, or as a lawn top-dressing when screened.
While most compost will greatly improve soils for plants, unfinished compost,
or compost resulting from anaerobic (without air) decomposition, can contain acids or
alcohols that can harm seedlings or sensitive plants.
Benefits of Compost
Compost improves the structure
of soil. When mixed with a sandy soil, compost holds moisture and inorganic minerals.
Compost particles hold soil together, and give it a crumbly texture. The addition of
compost increases the soil’s porosity so that plant roots can more easily penetrate it.
In heavy clay soil, compost
particles bind with clay particles to form larger particles. Surface water can drain between the larger
particles, while the compost portions hold moisture inside the particles for plant
uptake. Surface layers of soil conditioned with compost retain water better, and
resist surface crusting and erosion.
Compost attracts earthworms
and provides them with food, so they breed rapidly. The tunnels that earthworms create aerate
the soil and improve drainage, and the earthworms’ burrowing brings up minerals
from the subsoil, making them available to plants. Earthworms contribute to good soil
structure. They coat soil particles with humus, and stimulate the growth of fungi
that bind the soil particles together.
Although compost is considered
a soil conditioner, rather than a fertilizer, it contains both plant nutrients and essential trace
elements. Some chemical fertilizers release elements so quickly that rain can leach
them away before plants derive much benefit. In compost, most of the nitrogen and
phosphorous are held in organic form and released slowly. The nutrients in compost
are therefore available throughout the growing season.
Current research by several
plant pathologists indicates that incorporation of specific types of compost into soil will suppress
several soil born diseases on crops such as turf grass, peas, beans, and apples. This
research may have important implications
for compost use in coming years.
Compost is usually
applied annually. The thickness of compost application is determined by the landscape use, as
indicated in Table 5. The best time to dig compost into a garden bed is during
preparation of the bed for planting. If only a small amount of compost is available, it can be
incorporated in the seed furrow, or a handful can be added to each transplant hole of
annual or perennial plants. Large quantities can be used to transplant trees or shrubs
or to renovate or replace a lawn. Compost is also an excellent top-dressing around
flower and vegetable plants, shrubs, and trees.
For general soil enrichment, the soil
should be turned thoroughly, and compost mixed with the top 4 to 6 inches. Mixing fresh
clippings with compost provides additional nitrogen for plants and makes an excellent
mulching material. Care must be taken when incorporating compost around
plants to avoid injuring plant roots growing near the surface. Compost as surface mulch (or
top-dressing) provides nutrients that will gradually work their extremes and erosion
caused by hard rain.
Source: USDA publication ARM-NE-6, August
(1 BS/1,000 SQ. FT.)
and athletic field
|3,00 to 6,00
(1 to 2 inches)
|Incorporate into top 4 to 6
inches of soil
|| 400 to 800
(1/8 to ¼ inch)
|Broadcast uniformly on
|Shrub and tree
|200 to 400
(1/16 to ¼) inch
|Work into soil or use as a
|| Not more than 1/3 by
vermiculite, sand, or bark
Compost requirements for a
given area can be
calculated by noting that 3.1 cubic
yards, or 67
bushels, of compost are needed to
1,000 square feet with a 1-inch-deep
Compost applied to lawns must
ground, so that the grass is not
One way of applying the compost is to
aerator to slice up the sod. A
1/8-inch to 1/4-
inch covering of fine compost should
A rake or a rotary mower should be
used to distribute the compost into the crevices. Compost applied in this manner will
provide the grass roots with moisture and nutrients and prevent soil compaction.
Fine-textured compost can also
be used in
potting mixture formulations. No more
one-quarter to one-third, by volume,
potting mix should be compost; higher
levels can result in excess nutrient
Special care must be taken when using
compost for starting seedlings. While
recent research indicates that some
compost can help prevent dampingoff
disease of seedlings, fresh compost
may be phytotoxic and should not be used.
Compost containing brownish
bits of stems and stalks is still undergoing decomposition. Such compost should be
screened before it is applied to lawns or used in potting mixes. Screening will
produce a sifted, smoother soil. A simple screen can be made with ½-inch hardware
cloth and a wooden frame.
Additional web resources:
|| Possible Causes
||• Excess moisture
Turn pile, or add dry, porous material, such as sawdust, wood chips, or straw
• Turn pile,
or make pile smaller
Too much nitrogen
(lack of carbon)
Add high carbon material such as
sawdust, wood chips, or straw
Pile too small
• Lack of
Make pile bigger or insulate sides
• Add water
• Turn pile
• Mix in
sources such as grass
clippings or manure
size, or insulate pile with
an extra layer of material such
Pile too large
Reduce pile size
• Turn pile
Dogs and Cats
Presence of meat scraps or
Remove meat and fatty foods from
pile. Cover with a layer of fresh
compost, soil or sawdust,
or build an animal-proof
compost bin, or turn pile to
• Bury all
waste among brown materials
or active compost