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:
Pine needles used as mulch. Also called "pinestraw" in the southern U.S.to adjust soil temperature by helping soil retain more heat in spring and fall, and by keeping soil cool and evening out temperature swings during hot and variable summer conditions
to control weeds by blocking the sunlight necessary for germination
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
to incrementally improve growing conditions by reflecting sunlight upwards to the plants, and by providing a clean, dry surface for ground-lying fruit such as squash and melons.
for erosion control - protects soil from rain and preserves moisture
for sediment control - slows runoff velocity
A variety of materials are used as mulch:
organic residues - grass clippings, leaves, hay, straw, shredded bark, 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 - This relies on fully composted material, where potential weed seed has been eliminated, or else the mulch will actually produce weed cover.
plastic mulch - Crops grow through slits or holes in thin plastic sheeting. This method is predominant in large-scale vegetable growing, with millions of acres cultivated under plastic mulch 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.
rock and gravel can also be used a mulch. In northern climates the heat retained by rocks will extend the growing season.
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