Department of Plant and Soil Science
Leonard P. Perry, Extension Ornamental Horticulturist
Compost is a dark, crumbly, and earthy-smelling amendment
for soils, made from organic matter decomposed by microbes. It is a great amendment for soils, adding
nutrients and improving soil structure.
Compost improves both heavy clay soils and sandy soils. Since it breaks down over the year, it should
be added to soils yearly.
Compost is an easy way to recycle yard wastes without
hauling them to a landfill. Enclosures
can be as simple as a freestanding pile, to ones you make or buy. The procedure can be as simple as dumping organic
materials to rot on their own, which will take longer than adding certain
materials in layers and turning regularly.
The method depends on your goal—just to get rid of wastes, or to make a
soil conditioner as quickly as possible.
ENCLOSURES—These range from commercially available slatted
metal or plastic enclosures, perforated barrels and plastic-coated wire mesh
products, to those you can make yourself from wire- or snow-fencing, boards,
pallets, or cement blocks. All should
have frequent openings to allow for air movement. The size of the enclosure can be relatively
small—as with garbage can size units, or quite large. Generally, your enclosure should allow for
pile dimensions of 3 to 5-feet wide and no more than 5-feet high when
finished. Piles smaller than three feet
on each side likely will not get hot enough to work well, while piles larger
than five feet on each side may not allow enough air to reach the center. If no room for a larger pile, you can
compensate to some extent by using a black barrel or bin that will absorb heat from
the sun. Or you can insulate with straw bales.
You can make an enclosure from a 4 to 6 foot length of
turkey mesh wire, or reinforcing wire as used in concrete construction. Simply attach the ends together and you will
have formed a 3 or 4-foot diameter enclosure.
With several of these on hand, you can keep several piles going at
once. More elaborate structures can be
equipped with movable partitions to separate different lots of compost. I like to have more than one bin so I can
keep different ages of compost, or when turning move materials from one bin to
INGREDIENTS—Most any organic matter that was once alive can
be used to make compost. Waste from the
home that you should NOT add includes meat scraps, fatty foods (like cheese),
bones, pet manures, and litter. Waste from
the garden that you should NOT add includes weeds, diseased plant material, and
woody plant material that isn't chipped (it takes too long to break down
To make successful compost, four main ingredients are
needed—a source of carbon, a source of nitrogen, oxygen, and water. Carbon serves as an energy source for the
microbes that decompose organic matter, and nitrogen is needed for their
activity. All organic matter has a ratio of carbon to nitrogen (C:N). This ranges from 500:1 for sawdust to 15:1
for vegetable scraps. An ideal range for
compost microbes for fastest decomposition is 30:1. More carbon can be used, the pile will just
decompose slower. Since grass clippings
are 20:1 and leaves 60:1, a mixture of two part grass clippings to one part
leaves would be best. You don't need to
get concerned about exact ratios and weighing, just make sure to add lots more
carbon materials than nitrogen ones.
In general, coarse
and woody material is high in carbon.
Examples of good carbon sources for compost are wood chips, sawdust,
paper, straw, and leaves (shredded leaves decompose faster). In general, moist and dense material is high
in nitrogen. Examples of good nitrogen
sources for compost are manures, grass clippings, coffee grounds, and vegetable
waste. If too much carbon, the pile may decompose slowly. If too much nitrogen, you may smell
ammonia. A shredding machine, or rotary
mower for grass and leaves, chops materials into finer bits that decompose
PROCESS—Of course you can just add organic waste and scraps
to a bin to decompose on their own. This
is a good way to recycle, but may take a year or more to decompose. Faster compost requires a little more
organization and labor.
Once you have an enclosure, if other than open pile, and
begun gathering ingredients, start layering.
Layering helps you get the best proportions of ingredients, and mixed
well. As you add each layer or carbon or
nitrogen sources, moisten to the stage of a damp sponge. You may add a few shovels of soil, leftover
compost, or bagged compost to each layer to add microbes. Some stores sell compost starters containing
microbes. If short on nitrogen materials such as manures, some add a handful of
garden fertilizer for each bushel of organic matter.
As the microbes begin decomposition, the compost pile should
warm. You can check with your hand, or a
compost thermometer (a dial on a long rod) available at complete garden
stores. If it doesn't heat, or the heat
begins to decrease, add more high nitrogen materials. Check the pile for moisture regularly,
especially if a closed bin, and dampen if needed. Once the pile heats, then begins to cool, it
is time to turn it either in place or into an adjacent bin. This turning ensures adequate oxygen for the
microbes. Even if the pile doesn't warm
much, still turn it every few weeks. If
warm weather, and the compost pile is properly constructed and maintained, you
may see usable compost in two to six months.
PROBLEMS—If your compost pile isn't decomposing as quickly
as planned, here are some symptoms to watch (and smell) for.
*If you smell a bad or rotten odor, there may not be enough
air (anaerobic conditions), so turn the pile. The pile also may be too large,
or too wet.
*If you smell ammonia, there may be too much nitrogen, so
add more carbon materials.
*If you notice the center or the pile is dry, add more
*If the compost is damp and warm in the middle only, the
pile may be too small.
*If the compost is damp throughout, but won't warm, add more
*If the pile is too hot, it may be too large, or not be
getting enough air so need turning more often.
*Especially for larger piles, turn them more often. This
avoids anaerobic conditions as above.
*If the weather is cold, correct as for a small pile.
*If you have pests in the pile, such as raccoons or rats,
make sure there are no meat scraps or fatty foods.
KEYS TO SUCCESS—for the best and quickest compost, remember
these simple steps.
1. Provide the right ingredients.
2. Provide much more carbon than nitrogen.
3. Add ingredients in layers, and keep moist. A layer of soil may help.
4. Turn the compost often.
More on compost and related gardening topics can be found in
articles and leaflets on Perry’s Perennial Pages online (perrysperennials.info).
Return to Perry's Perennial
Adapted from a previous UVM Extension leaflet by Ed Bouton,
and leaflets from University
of Maine Cooperative Extension. 5/08
University of Vermont Extension and U.S. Department of
Agriculture, cooperating, offer education and employment to everyone without
regard to race, color, national origin, gender, religion, age, disability,
political beliefs, sexual orientation, and marital or familial status. Issued in furtherance of Cooperative Extension
work, Acts of May 8 and June 30, 1914, in cooperation with the United States
Department of Agriculture. University
of Vermont Extension, Burlington, Vermont.