A mulch is any material placed around plants as a protective covering on the soil. Mulching is a valuable tool in both the garden and the landscape as mulching reduces weed growth and therefore labour. Water run-off and erosion is controlled and soil moisture retained by a mulch. The mulch insulates the soil against temperature extremes; it slows soil warming in the spring reducing the danger of late frost to plants and extends the growing period in the fall by keeping the soil warm. Mulching keeps fruit and vegetables in the garden clean and makes a planting more attractive. A surface mulch prevents soil compaction, improving soil aeration, and moisture penetration, and thereby improving root growth.
A good mulch should be practical, inexpensive, easily obtained and easily applied. It should be heavy enough not to be blown around by the wind but should not pack so tightly that air and water are unable to penetrate it. Mulches such as straw may provide an over-wintering location for diseases, insects, and rodents, and the problems these cause may outweigh the benefits of the mulch. Some mulch materials may be a fire hazard so care must be used if they are close to a house.
Mulches can be used in vegetable and flower gardens, around trees and in shrub beds. They will inhibit weed growth as well as adding a top-dressing of organic matter to the soil. Mulches are usually applied around plants after the soil had been worked in the spring but before the hot weather approaches. If weeds grow through the mulch remove them by hand to avoid working the surface mulch into the soil.
Where sawdust is used as a mulch extra nitrogen must be applied to the soil so adequate nitrogen is available to the plants. In the first year apply 6kg of ammonium nitrate per lm3 of sawdust applied, in the second year 3kg of ammonium nitrate per lm3 of sawdust applied, and in the third year 1.2kg of ammonium nitrate per lm3 of sawdust applied.
Winter mulching moderates soil temperatures so there is less freeze-thaw action in the soil which can damage roots. A winter mulch should be applied in the fall after a hard frost. Evergreen boughs, straw, and reliable snow cover are all excellent winter mulches.