The most common reason for using a mulch is to help control weeds. Where the mulch is thick enough, usually four to six inches, very few weeds will grow. Mulches also help conserve moisture during periods of drought by reducing the amount of soil moisture lost through evaporation. At the same time, mulches maintain uniform levels of soil moisture, which is important in preventing blossom-end rot of peppers and tomatoes. Wide fluctuations in soil moisture may induce this physiological disorder.
Mulches also aid in maintaining a uniform soil temperature.
They act as an insulation, keeping the soil cooler during the warm months of the year. Organic mulch materials increase water-holding capacity of sandy soil and increase aeration of heavy clay soils as they gradually become mixed with the soil. Organic mulches also furnish food for microorganisms found in the soil. During decomposition of the organic material, soil microorganisms secrete a sticky material that promotes granulation of the soil. Mulch aids in preventing surface soil erosion, particularly if it has been established for a few weeks.