Mulch is a protective covering, usually of organic matter such as leaves or straw, placed around plants. It prevents the evaporation of moisture, the growth of weeds and (in cold climates) it prevents freezing of roots. It can have a positive effect on the fertility of the soil.
The layer of mulch also provides shelter and food for beneficial insects and spiders that feed on small insects that are present in the mulch (e.g. Collembola).
Mulching is a cultural practice often recommended in the cultivation of vegetables (tomato, okra, cucumber, lettuce, etc.) and fruit trees. It has been found to be useful in reducing populations of whiteflies and thrips. In many cases mulching helps to increase yields.
Care should be taken when pests are present that use the mulch as a hiding place or for pupating.