Digging In

Compost pile is a science unto itself

November 7, 2010

By: Jane Martin, Horticulturist


Compost pits hidden behind hedges in the Netherlands

Now that we've had temperatures dipping into the low 30s, it's time to gather garden debris and leaves and compost them, which is the green thing to do.

For those who are new to composting, some guidelines will help you get started.

Most of the time compost "happens" despite what you do or don't do to manage a pile. Successful composting is both art and science. A mix of green and brown matter is required; brown matter is high in carbon content; green matter is high in nitrogen content.

A carbon-to-nitrogen ratio of 30-to-1 is ideal for microbial activity. The compost pile will give you hints as to whether the mix is a good one.

For example, a pile will not degrade very quickly with too much brown matter, which can be remedied by adding a pound of urea (high nitrogen) fertilizer per cubic yard of debris. On the other hand, a pile will have a faint odor of ammonia with too much green stuff, which can be remedied by mixing in more brown stuff.

The size of the pile should range from 3 feet on all sides (27 cubic feet) to 5 feet (125cubic feet). Those sizes will allow proper heating but won't cut off oxygen to the center of the pile.

Build it in a well-drained area; debris can simply be piled on the ground or enclosed in snow fencing, wire mesh, concrete blocks or wood pallets.

Start by layering 3 to 4inches of coarse material, such as shrub branches. Next, add 6 to 8inches of mixed green and brown stuff. If it's shredded, breakdown will occur quicker.

Next, add a thin layer of soil or finished compost, which serves as a source of microorganisms. If you don't have much green stuff now, add nitrogen in the form of high-nitrogen fertilizer. Repeat until the pile reaches the desired size.

For the process to work, material in the pile should be damp, so watering might be needed initially. A properly constructed pile will reach about 140 degrees in four to five days and will begin to settle.

Finished compost is called 'black gold' because of its value as an amendment for improving clay soil. When finished, it is dark and crumbly, has an earthy smell and is within 10 degrees of air temperature. The original pile will degrade to be about one-third of its original size.

To use compost as a soil amendment; start by turning over the garden soil to be amended, then apply compost over the area at the rate of 1 to 3 inches and turn it in to a 6- to 8-inch depth. Some gardeners also layer compost in garden beds in the fall, an inch or two deep, which eventually aids soil structure.

Once you produce a good batch of compost, it's hard to quit, and most gardeners seem to increase the number or size of their piles. It's a good way to recycle yard waste on your own property!