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How Compost Becomes Compost

After you build a compost pile, nature does most of the work. Your job is to bring the raw materials together in a way that promotes decomposition. Successful composting requires four things:

A higher ratio of carbon to nitrogen is preferable; 30:1 is ideal. High carbon materials are commonly referred to as brown and high nitrogen materials as green. A variety of materials is desirable, with a rule of thumb being a ratio of five parts brown to one part green. (Its not 30:1 because every organic waste has a different ratio, ranging from 5:1 all the way to 500:1, so our five parts to one part is based on averages.) The composting process slows if there is not enough nitrogen, while too much nitrogen may cause the unpleasant odor of ammonia gas.

  • Organic matter, such as leaves, grass clippings, garden plants, kitchen scraps and shredded paper make excellent compost materials. Leaves, woody branches and paper have a high carbon content, which microorganisms need for energy. Grass clippings and vegetables are higher in nitrogen, needed to make the enzymes used in decomposition and other processes. Achieving an optimum balance of carbon to nitrogen (C:N ratio) is important for effective composting.

  • Soil organisms, such as bacteria, fungi and other decomposers, are largely responsible for the composting process. Since these organisms naturally occur in soil and vegetable matter, their presence is guaranteed. A couple shovelfuls of compost will make a great starter of decomposers for your next batch.

  • Water is essential for composting. A moisture level of 40 - 60 percent is best. Your compost pile should be about as wet as a wrung-out sponge. If it is too soggy, the bacteria and other beneficial organisms will not get enough air. On the other hand, a lack of moisture will cause microorganisms to go dormant and delay the composting process. Generally, the initial moisture will be adequate when grass clippings, vegetable trimmings or garden plants are used. Since leaves usually contain little moisture, a pile with large quantities of leaves will probably require the addition of water.

  • Oxygen is vital because composting is essentially an aerobic (requiring air) process. The bacteria need oxygen to live and multiply. If the air supply is cut off, anaerobic bacteria will take over, resulting in unpleasant odors. To ensure that enough oxygen is available, turn your compost pile. Turning also brings the outer, less decomposed portions of the pile into the center where the soil organisms do their work.