Organic material: A wide variety of organic materials are used for mulching. Some of the most common are straw, leaves, lawn clippings, wood chips, shredded bark, and ground corncobs. All organic mulches conserve soil moisture and modify the soil temperature near the surface. As these materials decompose, they improve the tilth of the soil. Choose a mulching material that is free of weed seeds, and that has not been recently sprayed with an herbicide. Apply organic mulches 3 to 6 inches thick. A thick mulch also controls weeds.

Inorganic material: These materials do not decompose, so they are more permanent than organic mulches. Inorganic mulches include rocks, gravel, and coarse sand. These materials are more expensive but longer lasting than organic mulches. There is also less danger of bringing weed seeds or diseases into your garden.

Impervious films: The most popular impervious film mulch is black polyethylene. Clear plastic and builder's paper are also used. Black plastic gives excellent control of weeds. It can even be placed over existing weeds to kill them. Films also control water loss and warm the soil slightly. Clear plastic does not control weeds, but warms the soil quickly, and can even be used to pasteurize the soil with heat (see Soil Fumigation and Solarization). Because plastic films reduce the amount of oxygen that penetrates the soil, do not use them over large areas around trees and shrubs.