|This how-to document contains information about
composting fundamentals for those interested in an introduction to
how composting should be done. In addition, a set of composting
questions and answers provide information about
how to tell if compost is finished, how to use
compost, and how compost benefits the soil.
As a composter, you can put as much effort as you like into your
composting system, but at its heart composting is really a very simple
process that needs only minimal maintenance. Once you understand the
basics, you will need to
choose a bin
system and build or purchase it (of course, binless compost piles
can work just fine as well). With an understanding of the
fundamentals, a spot set up for composting, and a few ingredients,
you'll be ready to build a compost pile.
Good composting is a matter of providing the proper environmental
conditions for microbial life. Compost is made by billions of microbes
(fungi, bacteria, etc.) that digest the yard and kitchen wastes (food)
you provide for them. If the pile is cool enough, worms, insects, and
their relatives will help out the microbes. All of these will slowly
make compost out of your yard and kitchen wastes under any conditions.
However, like people, these living things need air, water, and food.
If you maintain your pile to provide for their needs, they'll happily
turn your yard and kitchen wastes into compost much more quickly. Keep
in mind the following basic ideas while building your compost piles:
Composting microbes are aerobic -- they can't do their work
well unless they are provided with air. Without air, anaerobic
(non-air needing) microbes take over the pile. They do cause slow
decomposition, but tend to smell like putrefying garbage! For this
reason, it's important to make sure that there are plenty of air
passageways into your compost pile. Some compost ingredients, such as
green grass clippings or wet leaves, mat down very easily into slimy
layers that air cannot get through. Other ingredients, such as straw,
don't mat down easily and are very helpful in allowing air into the
center of a pile. To make sure that you have adequate aeration for
your pile and its microbes, thoroughly break up or mix in any
ingredients that might mat down and exclude air. You can also
turn the pile to get air into it, which means completely
breaking it apart with a spade or garden fork and then piling it back
together in a more 'fluffed-up' condition.
Ideally, your pile should be as moist as a wrung-out sponge to fit the
needs of compost microbes. At this moisture level, there is a thin
film of water coating every particle in the pile, making it very easy
for microbes to live and disperse themselves throughout the pile. If
your pile is drier than this, it won't be very good microbial habitat,
and composting will be slowed significantly. If your pile is a great
deal wetter, the sodden ingredients will be so heavy that they will
tend to mat down and exclude air from the pile, again slowing the
composting process (and perhaps creating anaerobic odor problems). If
you are using dry ingredients, such as autumn leaves or straw, you'll
need to moisten them as you add them to the pile. Kitchen fruit and
vegetable wastes generally have plenty of moisture, as do fresh green
grass clippings and garden thinnings. Watch out for far-too-soggy
piles in wet climates (a tarp may help to keep rain off during wet
weather). In dry climates, it may be necessary to water your pile
occasionally to maintain proper moisture.
In broad terms, there are two major kinds of food that composting
'Browns' are dry and dead plant materials such as straw, dry brown
weeds, autumn leaves, and wood chips or sawdust. These materials are
mostly made of chemicals that are just long chains of sugar molecules
linked together. As such, these items are a source of energy for the
compost microbes. Because they tend to be dry, browns often need to be
moistened before they are put into a compost system.
'Greens' are fresh (and often green) plant materials such as green
weeds from the garden, kitchen fruit and vegetable scraps, green
leaves, coffee grounds and tea bags, fresh horse manure, etc. Compared
to browns, greens have more nitrogen in them. Nitrogen is a critical
element in amino acids and proteins, and can be thought of as a
protein source for the billions of multiplying microbes.
A good mix of browns and greens is the best nutritional balance for
the microbes. This mix also helps out with the aeration and amount of
water in the pile. Browns, for instance, tend to be bulky and promote
good aeration. Greens, on the other hand, are typically high in
moisture, and balance out the dry nature of the browns. If you'd like
specific information on different materials, check the
'What to Compost'
OTHER THINGS TO CONSIDER
If you live in a cold climate, your compost pile will probably go
dormant in the winter. No problem -- it'll start back up again when
the springtime thaw comes.
A common misunderstanding about compost piles is that they must be
hot to be successful. This just isn't true. If you have good
aeration and moisture, and the proper ingredient mix, your pile will
decompose just fine at temperatures of 50 degrees Farenheit or above.
Hotter piles will decompose a bit faster, however. One way
to understand why this is so is to realize that the heat in a hot pile
is the result of the collective body heat of billions of microbes that
are busy digesting the ingredients in the pile. Generally speaking, a
hotter pile means more microbes or conditions that allow the microbes
to have faster metabolisms, and therefore a faster composting process.
If you'd like to keep your pile as warm as possible, consider the
For a pile to get hot and stay hot for a long period of time, the
typical minimum size for the pile is one cubic meter (a cube one
meter, or about three feet, on a side). A pile this size has plenty of
mass in which those billions of heat-generating microbes can live, yet
is also large enough that the center of the pile is well-insulated by
the material surrounding it. Smaller piles just cannot insulate
themselves well enough to remain hot for long, if at all. You can also
provide additional insulation to a pile by stacking bales of hay or
straw, or bags of dry autumn leaves, around your bin system. Some
people even used stacked hay bales to make bin systems (this
kind of bin will slowly compost itself, of course).
Composting Questions and Answers:
When is my compost finished?
Finished compost is dark in color and has an earthy smell (like the
smell of soil). Usually, it's difficult to recognize any of the
original ingredients, although bits of hard-to-decompose materials
(such as straw) sometimes can be seen.
There is no single point at which compost is finished -- it's a bit
more subjective than that. For many outdoor garden applications, for
instance, it can be fine to use compost that still has a few
recognizable bits of leaves or straw -- it will finish rotting in the
soil. If you plan to use compost in seed-starting mixes, though,
you're best off having a well-finished compost, because seedling roots
may be attacked by decomposer microbes if the roots contact unfinished
How can I use my finished compost?
To tell you the truth, well-finished compost looks so fine that I'm
tempted to eat the stuff sometimes. However, there are several more
common ways that compost can be used, on gardens, lawns, landscapes,