nyc compost project: mixing compost

mixing compost All compost organisms need a certain amount of water and air to survive. The amount of air and water in a compost pile will determine the rate of decomposition. Too much air circulating in the pile can make it too dry for bacteria to function. If the pile is too wet, anaerobic bacteria, which thrive in the absence of oxygen, can take over the pile. Anaerobic decomposition is slow, and can produce a rotten-egg odor and by-products that are toxic to plants.

WATER

In our New York City climate, materials usually require the addition of some water as they are added to a compost pile and they may continue to require watering over the course of decomposition. Optimal moisture levels for composting occur when materials are about as moist as a wrung-out sponge—obviously moist to the touch, but yielding no liquid when squeezed. This level of moisture provides organisms a thin film of water on the organic materials while still allowing air to circulate.

If a compost pile is too wet, it should be mixed frequently to allow air back into the pile and to loosen up the materials for better drainage. Dry, brown materials can also be added to absorb some of the moisture. Mixing materials of different sizes and textures also helps to provide a well-drained and well-aerated compost pile.

If a compost pile becomes dry, it needs to be pulled apart and watered as it is mixed. Watering an intact pile from above is not effective, because dry organic materials often shed water. Dry materials must be gradually wetted and mixed until they glisten with moisture. Prolonged exposure to rain can effectively soak a dry compost pile. It is best to cover a pile once materials are uniformly moist to retain moisture and prevent nutrients from leaching out.

AIR

To make sure that air can penetrate to the center of your pile, keep it no larger than 5 feet wide. A 1-cubic-yard pile (3 x 3 x 3 feet) is fine, and will be easier to turn. Also be sure to add lots of coarse materials to help air circulation, or aerate your pile by turning or mixing it periodically.

For smaller piles or enclosed compost bins—the methods most practical for dense, urban spaces—effective aeration can be achieved by using a long-handled rake or shovel or a compost crank (a specialized tool for turning compost also available at most compost givebacks). Just push the tool down into the center of the pile and "fluff" the pile up.

For more information, see:
• compost timing—how to tell when it's ready to use
• troubleshooting outdoor composting
• compost science

nyc compost project | how to compost | compost science | nyc compost resources
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