Cover crops are fast growing plants, usually grains, legumes or grasses, that are utilized by farmers and gardeners for one or more of their beneficial qualities and not usually intended as food crops.
Some of the benefits of cover crops are:
Weed control
Cover crops are fast growers so they are able to beat out weeds on the surface.
Disease/Pest control
Cover crops replace the diseased organisms that pests usually feed off of. This beneficial feature is also preventative.
Soil enrichment
When cover crops decay they leave behind organic matter.
Some cover crops have strong roots that help to break up tough soils.