For efficient composting, a compost pile must be large enough to hold heat and moisture, but small enough to admit air to the center.
A pile that is approximately one cubic yard (3 ft. tall x 3 ft. wide x 3 ft. long) is optimal for home compost piles.
- Small piles dry out quickly and cannot retain the heat required for quick composting.
- Piles that are larger than 5 ft. tall by 5 ft. wide of any length must be turned frequently or have air blown through the pile to prevent anaerobic conditions.
Bacteria become dormant when the temperature drops below 55ºF (13ºC). If properly built, a compost pile’s interior will stay well above that temperature even in freezing weather. Decomposition will slow during the winter months, but a pile built in the fall and kept covered should be reasonably finished by the spring.
To achieve optimum hot composting temperatures (140ºF or 60ºC) in any season, a minimum pile size is required. Otherwise, the heat generated by the initial organisms quickly dissipates before the pile can reach the right temperature for thermophilic organisms. A pile must be at least 3 feet in each dimension to provide the necessary critical mass.
For continuously composting household, yard and garden waste while maintaining optimum pile size, a “wandering compost pile” is effective. Starting with minimum dimensions of 3 feet high by 3 feet wide by 3 feet deep, this type of heap “wanders” as fresh ingredients such as kitchen refuse (minus meat or animal fat), are tossed onot the sloping front face and finished compost is sliced from the back. By screening the finished compost as it is removed and using the larger particles to cover additions to the front of the pile, newly added materials are seeded with the necessary microorganisms.