In agriculture and gardening, mulch is a protective cover placed over the soil, primarily to modify the effects of the local climate. A wide variety of natural and synthetic materials are used.

Mulch is used for various purposes:

• to adjust soil temperature by helping soil retain more heat in spring and fall
• to control weeds by blocking the sunlight necessary for growth
• to retain water by slowing evaporation
• to add organic matter and nutrients to the soil through the gradual breakdown of the mulch material
• to repel insects

A variety of materials are used as mulch:

• organic residues - grass clippings, leaves, hay, straw, sawdust, wood chips, shredded newspaper, cardboard, wool , etc. Many of these materials also act as a direct composting system. There are many differing opinions on what to use.
• compost
• plastic sheeting - Crops grow through slits or holes. This method is predominant in large-scale vegetable growing, with millions of square feet of plastic mulch used worldwide each year. (Disposal of plastic mulch is cited as an environmental problem.)
• organic sheet mulch - Various products developed as a biodegradable alternative to plastic mulch.

Mulching is an important part of any No-dig gardening regime, such as practiced within permaculture systems.

Application

Mulch is usually applied towards the beginning of the growing season, and may be reapplied as necessary. It serves initially to warm the soil by helping it retain heat. This allows early planting of certain crops, and encourages faster growth.

Plastic mulch used in large-scale commercial production is layed down with a tractor-drawn or standalone plastic mulch layer . This is usually part of a sophisticated mechanical process, where raised beds are formed, plastic is rolled out on top, and seedlings are transplanted through it. Drip irrigation is often required, with drip tape layed under the plastic, as plastic mulch is impermeable to water.

In home gardens and smaller farming operations, organic mulch is usually spread by hand around emerged plants. For materials like straw and hay, a shredder may be used to chop up the material. Organic mulches are usually piled quite high, six inches or more, and settles over the season.