A mulch is a layer of material that is spread over the surface of the soil to retain moisture and suppress weeds. Some mulches also add nutrients to the soil and improve soil texture. The most popular mulches are bark chips, cocoa shell and various blends of composted timber, bark, manure and green materials. Your own homemade garden compost can also be used as a mulch. Coarse mulches such as bark chips are decorative in their own right. Mulches should only be applied to warm moist soil. If you spread them when the soil is cold or even frozen it will take a long time for the soil to warm up. If you apply them when the soil is dry it may take a long time for rain to penetrate. The best times to apply a mulch are in the autumn as a way of protecting the soil and stop nutrients leaching out, and in late spring when the soil has started to warm and weeds are beginning to grow.