A mulch is any non-living material used to cover the soil. That’s a broad definition, including a number of different materials, each with their own uses and drawbacks. This section categorizes different types of mulches.
Particle mulches include straw, sawdust, gravel, and pine cones — mulches that are composed of separate pieces. They are spread by wheelbarrow and shovel to the depth required. Some — the organic mulches — rot slowly or quickly to improve the soil. They must be replace regularly, usually once a year, as they decompose.
Mineral mulches and coarse organic material, such as fir bark chunks, last for years and can be thought of as nearly permanent if they are cared for. These materials are usually used as mulches in ornamental areas. Many different types of river rock, gravel, and decomposed rock materials make attractive and long-lasting ornamental mulches that prevent weeds, conserve water, and benefit the plants growing through them.
Many of the same materials are used as both mulches and soil amendments. The difference between a soil amendment and a mulch is not in the nature of the material but in the method of application: a soil amendment is incorporated into the soil, using a tiller or spade, to improve the soil’s texture and structure. A mulch is applied in a fairly thick layer on top of the soil, and although it performs some of the functions of an amendment, a mulch has a number of other effects.
Film mulches may be made of plastic, roofing paper, or aluminum foil. These impermeable films have different characteristics than particle mulches. As long as they remain unbroken, they absolutely prevent weed growth and evaporation from the soil. Their effect on soil temperature depends on the material.
Most film mulches are unattractive, but they can be hidden with a layer of a more attractive mulch. Film mulches are simple and quick to spread, but usually only last one season; most decompose in the sun, becoming weak and tattering before long.