Other nutrients such as phosphorus and potassium are usually present in adequate amounts for decomposition. During the initial states of decomposition organic acids are produced, decreasing the pH. In the past, small amounts of lime have been suggested for maintaining and enhancing microbial activity at this time. However, high rates of lime will convert ammonium nitrogen to ammonia gas which will lead to the loss of nitrogen from the pile. In general, lime is not necessary for degradation of most yard wastes. If large quantities of pine needles, pine bark, or vegetable and fruit wastes are composted, additional lime may be necessary.
Many organic materials are suitable for composting.
Yard wastes, such as leaves, grass clippings, straw, and non woody plant trimmings can be composted. Leaves are the dominant organic waste in most backyard compost piles. If clippings are used, it is advisable to mix them with other yard wastes, otherwise the grass clippings may compact and restrict airflow. Kitchen wastes such as vegetable scraps, coffee grounds, and eggshells may also be added. Sawdust may be added in moderate amounts if additional nitrogen is applied.