Given even remotely acceptable materials and conditions, compost will occur over time. The breakdown of organic matter is a normal part of nature’s cycle. To create compost in a timely manner and of quality that is useful in our gardens, it helps to understand how some factors influence the composting process.
Carbon and Nitrogen supplying material — These materials are the food and energy sources for the microorganisms that facilitate the compost process. They will also provide numerous nutrients to feed our plants once broken down into their chemical components.
Air — Composting is an aerobic process; that is one that takes place in the presence of oxygen. Lacking oxygen, the process will become anaerobic. The pile will ferment and may start to smell. The compost pile needs to contain some pore space to allow for the presence of air. Mixing small particles with larger coarse particles will create needed pore spaces. Turning the pile as broken down material starts to settle and the process slows down, also fluffs up the pile and introduces air to keep the oxidation process moving.
Moisture — This is possibly the most important factor influencing the composting process. Ideally, you want to maintain a moisture content between 40 and 60% — that is moist, but not dripping — much like a wrung out sponge. If you can squeeze moisture from your compost it is too wet. In wet areas or rainy seasons, covering the compost pile may be needed. Likewise, in the heat of a dry summer, you may need to water your pile; just as you would your garden, if there is not enough natural rainfall.
Temperature — The compost process typically takes place best between 120 and 150 degrees F. This is the temperature range within which the microbes involved in the process function best and reproduce to keep the process moving. If weeds with seed heads are thrown on the pile, as is often the case, the seeds will lay dormant to sprout later in your garden unless the pile becomes sufficiently hot to kill the seeds. This is typically achieved at 130 degrees F or above. Compost piles smaller than a cubic yard may not heat up sufficiently to kill weed seeds.
Particle size — Smaller particles have more surface area exposed for microorganisms to populate. Consequently, smaller particles will be broken down more quickly to a useful compost. When adding coarse materials to the pile such as woody branches, corn cobs, or tough plant stalks, it is helpful to chip, grind, or cut up these materials for faster composting.
Pile size or volume — Small volume compost piles have a tendency to dry out too quickly and require more frequent watering. In northern climates the winter temperatures may be too cold to allow composting to occur on the exterior of the pile. If the pile volume is large enough, as suggested earlier, the interior of the pile will continue to “work,” albeit at a slower pace.
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Compost Conundrums — Troubleshooting your compost pile