FACTSHEET NO. 6
Revised Nov. 1994
HOW TO PREPARE YOUR OWN COMPOST
Dr. John M. Gerber
Plant materials, animal manures and soil
microorganisms are combined in a pile to create valuable
compost. Compost is partially decomposed organic material
which, when added to the garden, improves both the
physical structure and fertility of the soil. Annual additions
of compost and other organic materials will provide benefits
that may not be immediately apparent but improve the soil
As partially decayed organic matter continues to
decompose in the soil, fine soil particles are collected
together into larger crumb-like masses. These larger
particles will not pack as close together as smaller particles.
This action will improve drainage and aeration and will
"lighten" heavy clay soils.
Sandy, well-drained soils made up of primarily large
size soil particles are likely to dry out rapidly and cause
plants to wilt. Additions of organic matter such as compost
will increase the ability of sandy soils to retain moisture and
As compost decomposes in the soil, plant nutrients are
slowly released to the plant. Although this will not supply all
the nutrients required for optimum growth, it will help supply
most of the plant nutrients required in small amounts (trace
elements). Nutrients required in large amounts, such as
nitrogen, phosphorus and potassium, should be supplied in a
concentrated form, such as 10-10-10 fertilizer for maximum
yields. However, the gardener who is not concerned with
maximum production can supply adequate nutrition using
only manure and compost. Annual applications of 4 bushels
of manure per 100 sq. ft. plus generous amounts of
compost will produce adequate yields.
All plant and animal material will eventually decay if it
is exposed to warm, moist conditions. The compost pile
provides those conditions so that the microorganisms can
rapidly decompose organic materials.
BUILDING THE PILE
A compost built of primarily dry material such as
brown grasses and palm fronds will decompose very
slowly due to a lack of nitrogen and water. The addition of
moist, green matter helps supply both nitrogen and
moisture necessary for microorganisms to live.
A compost built of primarily fresh, green materials,
such as grass and kitchen wastes, will decompose very
rapidly. However, green material lacks bulk. The pile will
shrink in size as water is lost, leaving a small volume of
Successive layers of moist or green organic materials
should be alternated with dry, brown material. Each layer
should be no more than 8 inches deep to allow proper
mixing. Approximately equal proportions of moist and dry
materials would be ideal, however, a 2:1 ratio of dry to
moist material is acceptable.
The pile should be at least 4 ft. long by 4 ft. wide and
4 ft. high. A smaller pile will dry out too fast. The optimum
size for your compost pile is 7 ft. long by 7 ft. wide at the
bottom and 5 ft. high. This pile will retain the moisture and
heat necessary for decomposition. If it gets much larger, air
will not get to the center of the pile. A compost that lacks
air will emit odors similar to rotting garbage.
The pile can be enclosed in a wire cage or a cinder
block bin for convenience. Wooden enclosures decompose
too rapidly for use in the tropics.
Most organic refuse, such as weeds, old plants, fallen
leaves, kitchen wastes and grass clippings, can be saved
for composting. Diseased plant materials should be burned
and the ashes may be included in the compost. Scraps of
meat and animal bones should not be included because
they will attract rodents. Vegetable wastes from the
kitchen can be put in the pile if they are buried. Sewage
sludge is not recommended because it may contain toxic
heavy metals such as cadmium and lead.
Coarse materials, such as tree branches, twigs and palm
leaves, will take too long to decompose when added to the
compost. Although a small amount of these materials will
help aerate the pile, too much can increase the rate of dry-
ing and slow down decomposition.
A partial list of acceptable materials includes:
sawdust (from untreated wood)
rotted fruits and vegetables
(m) = moist material
(d)= dry material
SHREDDING THE MATERIALS
Chopping the materials into smaller pieces is not
necessary, however, it will greatly increase the rate of
decomposition. This is especially true for the coarse, dry
ingredients. Grasses can be chopped up with a lawn
mower but more fibrous materials should be put through a
chopper-shredder. Large leaves, such as banana, can be
cut into smaller pieces with a machete.
TURNING THE PILE
A pile that is built in layers as described above should
be turned about 4 weeks after building. It should be turned
7 ~T~ J
a second time 3-4 months later.
For most gardeners it is difficult to obtain all the
materials at one time. Therefore, most piles are built as
materials become available. This type of pile must be turned
more often. Whenever you have a lot of material to add,
turn the pile and mix in the new material.
It may be convenient to turn compost contained in one
enclosure into another. Two cinder block bins side by side
make turning easier and also make a well-shaped, neat pile.
COVERING THE PILE
All above ground compost piles in the Virgin Islands
must be moistened and covered. The tropical sun and
drying winds will dehydrate a pile before decomposition can
begin. A black plastic cover will help retain moisture and
also increase the heating of the pile. A plastic cover will
also protect the pile from heavy rains which may wash
away valuable nutrients.
THE PIT COMPOST
Another means of keeping the pile moist is to build it
under ground. Dig a hole about 4 ft. deep and 4-6 ft. wide.
Mix the ingredients as described for the above ground com-
post and moisten the materials. The pit should then be
.-II r: rI -I r
-= ~--' -
o .rrrn nor~
-s On~ al0l
r ~ r; -g rIn S
-a a -s
composting and possibly reduce the odor and rodent
REQUIREMENTS FOR A GOOD COMPOST
1. Microorganisms, such as bacteria and fungi
(molds) are needed to decompose the organic materials.
These microorganisms "eat" organic matter and produce
humus. The microorganisms that decompose organic
materials in the Virgin Islands are found in our soils.
2. The microorganisms require a food source to live
and grow. The food is the compost itself, the dried grasses,
the manure, the eggshells, etc. The bulk of the food is
made of dry materials which are used by the
microorganisms for energy. The rest of the food is supplied
by fresh, green materials which are needed for water,
nitrogen and other nutrients. The microorganisms "eat" this
"food" and leave humus and other decomposition products.
3. A hospitable environment for the microorganisms
to live and grow is necessary. This environment should be
warm and moist, yet contain enough air for the micro-
organisms to breathe. The failure of most compost piles is
usually due to the lack of a hospitable microbial environ-
ment. In the Virgin Islands, drying out of the pile is the
PROBLEMS AND SOLUTIONS
What should you do if your compost doesn't work?
First check the following list of possibilities. Then, should
you not find the answer to your problem, call the
Cooperative Extension Service of the College of the Virgin
1. Too wet. This problem is not very likely in the
Virgin Islands due to the hot tropical sun, yet it is a
possibility. When a pile becomes waterlogged it will not
decompose rapidly due to lack of air for the
Although decomposition without air will occur, (as in
a pit compost), the pile will emit an offensive odor. A well-
aerated, moist pile will not emit such odors.
A plastic cover during the rainy season will prevent
over-saturation of the pile. If your pile continues to be wet,
you may turn in some fibrous material such as corn stalks
or dry grass. The turning action as well as the dry material
will help aerate the pile.
2. Fertilizer (1 cup/layer)
3. Leaves, manure, etc.
covered with several inches of soil. This compost will work
without air, however it will smell like rotting garbage and
may also attract more rodents and cockroaches than the
above ground pile. The addition of ammonium sulfate
(21-0-0) or 10-10-10 fertilizer will increase the rate of
If the pile is larger than the recommended size, the
center may stay wet and lack air. A pipe with holes in it,
placed vertically through the center, will help aerate the
2. Too dry. Drying of the pile is the number one
problem with composts in the islands. Many composts dry
up and blow away before they can decompose. Drying can
be prevented by not putting large branches and palm fronds
in the pile. Including a substantial portion of fresh manure,
green leaves and kitchen wastes will also help prevent
All above ground composts in the islands should be
moistened and covered with black plastic. This will prevent
drying and encourage decomposition.
3. Lack of nitrogen. Nitrogen is needed by
microorganisms as well as by plants. A pile made of
primarily dry materials such as dead grass and sawdust
may be lacking nitrogen. Without adequate nitrogen, the
microorganisms will not grow and the pile will not
Nitrogen is usually supplied by fresh green organic matter.
If green materials are not available, you should add
nitrogen fertilizer. Approximately one-half pound of
ammonium sulfate (21-0-0) or one pound of 10-10-10
fertilizer should be mixed in each bushel of compost. The
pile should then be moistened and covered.
4. Lack of microorganisms. The bacteria and fungi
that decompose organic materials exist everywhere in the
islands. Failure of a pile due to lack of microorganisms
would be a very rare occurrence. The addition of several
shovels of garden soil will insure that the pile contains the
proper organisms. Commercially prepared compost activa-
tors are not necessary.
5. Acidity too high. Most decomposing plant and
animal materials tend to acidify the pile. Many micro-
organisms cannot survive acid conditions. Since many soils
in the Virgin Islands are quite alkaline, the soil added to the
pile should neutralize the acidity. If your soil is not alkaline,
you may add lime to the pile. Approximately 3-5 pounds of
lime in a 5 ft. by 5 ft. by 5 ft. pile should be adequate.
Products and suppliers mentioned by name in this publication are used as examples and in no way imply endorsement or recommendation of these products or suppliers
Issued in furtherance of Cooperative Extension work, acts of Congress of May 8 and June 30, 1914 (as amended), in cooperation with the U S Department of Agriculture,
D S Padda, Director, College of the Virgin Islands Cooperative Extension Service The College of the Virgin Islands Cooperative Extension Service is an Equal
Opportunity/Affirmative Action organization, providing educational services in the field of agriculture, home economics, rural development, 4-H youth development and related
subjects to all persons regardless of race, color, religion, sex or national origin