Mulch
A layer of material spread over soil to hold moisture, keep down weeds and protect roots.
Mulch covers bare soil. Organic mulches include bark chips, straw, leaf mould, garden compost, coconut husk and dry leaves. As they rot they feed the soil. A layer a few centimetres thick slows evaporation, blocks light from weed seeds and keeps roots cooler in heat and warmer in frost. Gravel is used as mulch around alpines and succulents, which rot if their necks stay wet. Mulch is best laid on soil that is already moist.