Composting is a microbial process that converts plant materials such as grass clippings and leaves to a more usable organic soil amendment or mulch. Gardeners have used compost for centuries to increase soil organic matter, improve soil physical properties, and supply some of the essential nutrients for plant growth. Mulching refers to the practice of applying a layer of materials such as compost, leaves, or grass clippings to the soil surface in order to modify soil temperature and moisture as well as control weeds and soil erosion.