The art of composting
has been part of our global culture since ancient times.
The basic principles are quite simple, and adhering to
them will result in an efficient and
successful outcome. Studies have shown that home composting
can divert an average of 700 lbs. of material per household
per year from the waste
stream. Municipal composting carries a greater environmental
cost, but not nearly as high as if leaf and yard waste
are disposed of by conventional
means. Composting is an excellent way to avoid both wasting
useful, natural resources and creating environmental
problems, while at the
same time producing a high quality and inexpensive soil
Composting is the transformation of organic material
(plant matter) through decomposition into a soil-like
material called compost. Invertebrates (insects and
earthworms), and microorganisms (bacteria and fungi)
help in transforming the material into compost. Composting
is a natural form of recycling, which continually occurs
An ancient practice, composting is mentioned in the
Bible several times and can be traced to Marcus Cato,
a farmer and scientist who lived in Rome 2,000 years
ago. Cato viewed compost as the fundamental soil enhancer,
essential for maintaining fertile and productive agricultural
land. He stated that all food and animal wastes should
be composted before being added to the soil. By the
19th century in America, most farmers and agricultural
writers knew about composting.
Today there are several different reasons why composting
remains an invaluable practice. Yard and food wastes
make up approximately 30% of the waste stream in the
United States. Composting most of these waste streams
would reduce the amount of Municipal Solid Waste (MSW)
requiring disposal by almost one fourth, while at the
same time provide a nutrient-rich soil amendment. Compost
added to gardens improves soil structure, texture, aeration,
and water retention. When mixed with compost, clay soils
are lightened, and sandy soils retain water better.
Mixing compost with soil also contributes to erosion
control, soil fertility, proper pH balance, and healthy
root development in plants.
The standard means of disposal for most yard and food
waste include landfilling and incineration. These practices
are not as environmentally or economically sound as
composting. Yard waste which is landfilled breaks down
very slowly due to the lack of oxygen. As it decomposes,
it produces methane gas and acidic leachate, which are
both environmental problems
Landfilling organic wastes also takes up landfill space
needed for other wastes. Incinerating moist organic
waste is inefficient and results in poor combustion,
which disrupts the energy generation of the facility
and increases the pollutants that need to be removed
by the pollution-control devices. Composting these wastes
is a more effective and usually less expensive means
of managing organic wastes. It can be done successfully
on either a large or small scale, but the technique
and equipment used differ.
Decomposition occurs naturally anywhere plants grow.
When a plant dies, its remains are attacked by microorganisms
and invertebrates in the soil, and it is decomposed
to humus. This is how nutrients are recycled in an ecosystem.
This natural decomposition can be encouraged by creating
ideal conditions. The microorganisms and invertebrates
fundamental to the composting process require oxygen
and water to successfully decompose the material. The
end products of the process are soil-enriching compost,
carbon dioxide, water, and heat.
Composting is a dynamic process which will occur quickly
or slowly, depending on the process used and the skill
with which it is executed. A neglected pile of organic
waste will inevitably decompose, but slowly. This has
been referred to as "passive composting,"
because little maintenance is performed. Fast or "active"
composting can be completed in two to six weeks. This
method requires three key activities; 1) "aeration,"
by turning the compost pile, 2) moisture, and 3) the
proper carbon to nitrogen (C:N) ratio. Attention to
these elements will raise the temperature to around
130=-140=, and ensure rapid decomposition.
The success with which the organic substances are composted
depends on the organic material and the decomposer organisms
involved. Some organic materials are broken down more
easily than others. Different decomposers thrive on
different materials as well as at different temperature
ranges. Some microbes require oxygen, and others do
not; those that require oxygen are preferable for composting.
A more diverse microbial community makes for a more
efficient composting process. If the environment in
the compost pile becomes inhospitable to a particular
type of decomposer, it will die, become dormant, or
move to a different part of the compost pile. The transforming
conditions of the compost pile create a continually
evolving ecosystem inside the pile.
All organic material
will eventually decompose. The speed at which it decomposes depends
- carbon to nitrogen
ratio of the material
of surface area exposed
or oxygen in the pile
- temperatures reached
in compost pile
- outside temperatures
Carbon and nitrogen are the
two fundamental elements in composting, and their ratio
(C:N) is significant. The bacteria and fungi in compost digest or "oxidize" carbon
as an energy source and ingest nitrogen for protein synthesis. Carbon
can be considered the "food" and nitrogen the digestive
The bulk of the organic matter
should be carbon with just enough nitrogen to aid the decomposition
process. The ratio should be roughly 30 parts carbon to 1 part nitrogen
(30:1) by weight. Adding 3-4 pounds of nitrogen material for every
100 pounds of carbon should be satisfactory for efficient and rapid
composting. The composting process slows if there is not enough nitrogen,
and too much nitrogen may cause the generation of ammonia gas which
can create unpleasant odors. Leaves are a good source of carbon; fresh
grass, manures and blood meal are sources of nitrogen.
Decomposition by microorganisms
in the compost pile takes place when the particle surfaces are in
contact with air. Increasing the surface area of the material to be
composted can be done by chopping, shredding, mowing, or breaking
up the material. The increased surface area means that the microorganisms
are able to digest more material, multiply more quickly, and generate
more heat. It is not necessary to increase the surface area when composting,
but doing so speeds up the process. Insects and earthworms also break
down materials into smaller particles that bacteria and fungi can
The decomposition occurring
in the compost pile takes up all the available oxygen. Aeration is
the replacement of oxygen to the center of the compost pile where
it is lacking. Efficient decomposition can only occur if sufficient
oxygen is present. This is called aerobic decomposition. It can happen
naturally by wind, or when air warmed by the compost process rises
through the pile and causes fresh air to be drawn in from the surroundings.
Composting systems or structures should incorporate adequate ventilation.
Turning the compost pile is
an effective means of adding oxygen and brings newly
added material into contact with microbes. It can be done with a pitchfork
or a shovel,
or a special tool called an "aerator," designed specifically
for that purpose. If the compost pile is not aerated,
it may produce an odor symptomatic of anaerobic decomposition.
Microorganisms can only use
organic molecules if they are dissolved in water, so
the compost pile should have a moisture content of 40-60 percent. If
the moisture content
falls below 40 percent the microbial activity will
slow down or become dormant. If the moisture content exceeds 60 percent,
aeration is hindered,
nutrients are leached out, decomposition slows, and
the odor from anaerobic decomposition is emitted. The "squeeze test" is
a good way to determine the moisture content of the
composting materials. Squeezing a handful of material should have the
moisture content of
a well wrung sponge. A pile that is too wet can be
turned or can be corrected by adding dry materials.
Microorganisms generate heat
as they decompose organic material. A compost pile
with temperatures between 90= and 140=F (32=-60=C) is composting efficiently.
higher than 140=F (60=C) inhibit the activity of many
of the most important and active organisms in the pile. Given the high
required for rapid composting, the process will inevitably
slow during the winter months in cold climates. Compost piles often
steam in cold
weather. Some microorganisms like cool temperatures
and will continue the decomposition process, though at a slower pace.
Backyard composting can be done
using a variety of different systems, enclosures, or containers. Composting
systems or bins can be constructed at home or purchased commercially.
Depending on where you live, youmay have a problem with rodents if vegetative
food wastes are combined with yard wastes. If so, an enclosed space
or bin is advisable. The methods employed will vary somewhat depending
on the system you choose, but the principles and purpose remain the
same. This is true for large-scale composting projects as well.
Some municipalities collect
yard waste at the curbside similar to the way recyclables are collected.
It is taken to a central location and formed into windrows, triangular-shaped
rows from 5 to 8 feet high and as long as necessary. Turning for aeration
is done about once a month using a front-end loader or other type of
heavy equipment made specifically for that purpose. The temperature
and moisture are checked twice a week. The finished compost may be sold,
given away, or used by the municipality in public works projects. Backyard
composting eliminates the environmental and economic costs of the heavy
equipment used to bring yard waste to a composting site and turn the
Vermicomposting or worm composting
is the easiest way to recycle food wastes and is ideal
for people who do not have an outdoor compost pile. Composting with
the needless disposal of vegetative food wastes and
enjoy the benefits of a high quality compost. It is done with "redworms" (Eisenia
foetida) who are happiest at temperatures between 50= and 70= F and
can be kept indoors at home, school, or the office. As with outdoor
composting, it is best to avoid putting bones, meats, fish, or oily
fats in the worm box as they emit odors and may attract mice and rats.
When cared for properly, worms process food quickly and transform
food wastes into nutrient-rich "castings." Worm castings
are an excellent fertilizer additive for gardens or
The redworms are placed in
a box or bin which can be built or purchased, along
with "bedding" of
shredded cardboard and/or paper moistened to about
75% water content. The container should be wide enough so that food
scraps can be buried
in a different location each time. The dimensions of
the container and the amount of worms required initially will depend
on how much
organic food waste will need to be composted each week.
The worms will gradually reproduce
or die according to the amount of food they receive.
A sudden addition of a large amount of food waste may attract fruit
flies, so increases
should be made gradually. In a healthy box, worms can
build large populations and consume four to six pounds of food scraps
About four to six months after the box has been started,
the worms will have converted all of the bedding and most of the food
into "castings" which will need to be harvested so the process
can begin again.
Food waste digestors are an
option for people who want to reduce the amount of
food waste they produce but do not have a compost pile. These units
produced compost bins, but differ in purpose. They
are designed to accept food wastes otherwise inappropriate for composting
meats, fish, fats, or oily food scraps. In general
they are built to prevent odors from being released and prevent rodents
the unit. Food waste digestors are fundamentally different
from worm boxes and compost piles, because the digestors do not ultimately
a soil enhancing product. Their purpose is to cut down
on the volume of food waste generated. Food waste digestors are not
hole in the ground" however, and the decomposed food residue
must periodically be emptied into the trash.