Mulch, any material, usually organic, that is spread on the ground to protect the soil and the roots of plants from the effects of soil crusting, erosion, or freezing; it is also used to retard the growth of weeds. A mulch may be made of materials such as straw, sawdust, grass clippings, peat moss, leaves, or paper. For large areas under cultivation a tilled layer of soil serves the purpose of a mulch.
A layer of bark, peat moss, compost, shredded leaves, hay or straw, lawn clippings, gravel, paper, plastic, or other material spread over the soil around the base of plants. During the growing season, a mulch can help retard evaporation, inhibit weeds, and regulate soil temperature. In the winter, a mulch of evergreen boughs, coarse hay, or noncompacting leaves can help protect plants from heaving.
Organic mulches decay over time and are temporary. The way a particular organic mulch decomposes and reacts to wetting by rain and dew affects its usefulness.
Organic mulches can negatively affect plant growth when they are decomposed rapidly by bacteria and fungi, which require nitrogen that they remove from the surrounding soil. Organic mulches can mat down, forming a barrier that blocks water and air flow between the soil and the atmosphere. Some organic mulches can wick water from the soil to the surface, which can dry out the soil.