Cover crops grow between or under a main crop are called

Leguminous crops are often very good cover crops. Summer annual legumes, usually grown only during the summer, include soybeans, peas, and beans. Winter annual legumes that are normally planted in the fall and counted on to overwinter include Austrian winter field peas, crimson clover, hairy vetch, and subterranean clover. Some, like crimson clover and field peas, can overwinter only in regions with mild frost. Berseem clover will overwinter only in hardiness zones 8 and above. Hairy vetch is able to withstand fairly severe winter weather. Biennials and perennials include red clover, white clover, sweet clover, and alfalfa. Crops usually used as winter annuals can sometimes be grown as summer annuals in cold, short-season regions. Also, summer annuals that are easily damaged by frost, such as cowpeas, can be grown as a winter annual in the deep southern United States.

One of the main reasons for selecting legumes as cover crops is their ability to fix nitrogen from the atmosphere and add it to the soil. Legumes that produce a substantial amount of growth, such as hairy vetch and crimson clover, may supply over 100 pounds of nitrogen per acre to the next crop. Legumes such as field peas, bigflower vetch, and red clover usually supply only 30 to 80 pounds of available nitrogen. Legumes also provide other benefits, including attracting beneficial insects, helping control erosion, and adding organic matter to soils.

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