Best Bets: Plants for Particular Uses
Cover crops are often transition plantings used in crop rotation or before establishing more permanent landscaping to improve soil texture, water infiltration, or fertility. They can be used in barren areas where soil is depleted, compacted, or eroded, but they also can serve as green mulch in beds. Many store nitrogen in soil, which promotes growth of later plantings.
The sequence above is of a bed planted with clover and oats in the Organic Vegetable Garden in the fall of 2020. The Extension Master Gardeners turned over the beds in April 2021. They waited about 3 weeks to plant this bed to allow the organic material to decompose. Photos by Judy Salveson & Judy Johnson.
The winter and summer cover crops and mixes described here are used at the MGNV Demonstration Organic Vegetable Garden located in the Potomac Overlook Regional Park (2845 Marcey Road, Arlington, Virginia). Visitors are welcome to observe the crops growing there during the appropriate seasons.
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Winter Cover Crops*
Crimson Clover (Trifolium incarnatum)
Plant from late August through September, alone or with winter rye or other cover crops. Produces dense green carpet by early winter and crimson blossoms by early May. Fixes nitrogen. Builds soil. Shade tolerant. Attracts beneficial insects. Does not multiply with runners. Cut at soil level when blooms start to fade and before seeds form. For a green manure, till cut tops into soil 2–3 weeks before planting something else. Alternatively, use cut tops as mulch around subsequent plantings and till into soil at the end of season.
Field Peas (Pisum sativum subsp. arvense)
Plant from late summer to early fall, alone or with oats or other cover crops. Excellent nitrogen source. Hardy to 10 degrees. Good choice for areas planted in early spring, especially with oats. Oats add biomass, hold plant nutrients, and, like field peas, are fairly easy to till into soil. Turn under 2–3 weeks before planting something else.
Oats (Aveena sativa)
Plant from late summer to early fall alone or with field peas or other legumes. Suppresses weeds, prevents erosion, adds biomass, and captures excess nutrients. May be killed by cold in winter, making it easier to till into the soil in spring for early crops.
Winter Rye (Secale cereale)
Plant September to October with nitrogen fixing cover crops such as crimson clover or hairy vetch. Adds plentiful organic matter, enhances soil life, and suppresses weeds. Extensive root system improves soil structure. Does not fix nitrogen, but captures excess nitrogen and other nutrients. May be tilled under in spring while still succulent about four weeks before planting another crop. Rye tends to regrow when it is tilled under at less than 12 inches tall. For more organic matter, cut after flowering, but before seeds form and use tops as mulch for later crop. Best used in areas where later season crops will be planted.
Hairy Vetch (Vicia Villosa)
Plant with winter rye or other cover crops in early fall. Excellent nitrogen source. Grows slowly in fall, then rapidly in spring. The combination with rye ensures good ground cover over the winter and the rye allows the vetch to climb in spring. Cut Hairy Vetch to terminate growth before or as soon as you see its purple flowers. It can easily become a weed if allowed to produce seed.
Winter Cover Mixtures*
Plant cover crop seed mixtures for winter cover from early September through mid October. Cover crop mixtures may contain two, three or several different cover crops and are often more effective than a single species planted alone. A mix can combine the nitrogen fixing effects of one or more legumes with the soil building properties of one or more grains or other plant species
Summer Cover Crops*
Buckwheat (Fagopyrum esculentum)
Plant from June through July as a quick cover crop between spring and fall plantings (after early lettuce and before fall kale or after spring pansies and before fall mums). Grows quickly up to 24 inches, producing abundant small white flowers in 5 to 6 weeks. Attracts beneficial insects, including pollinators for summer crops. Smothers weeds. Stores phosphorus to release for next crop. To prevent reseeding, cut before dark seeds form in flowers. Stems and roots are easy to cut up and till into soil.
Cowpeas (Vigna unguiculata)
Plant in late spring after soil has completely warmed as this crop is frost sensitive. Fast-growing in hot weather. High nitrogen producer and good soil builder. Cowpeas are edible (black-eyed peas and crowder peas are varieties of cowpea). Cut cowpeas after pod formation for higher nitrogen production. If pods are allowed to mature for harvest as a food crop, cut and till into soil as soon as harvest is complete to prevent stink bug attraction.
*The planting schedules described above are for winter cover crops in USDA Plant Zone 7
- Fleming, Cathy and Wade Thomason. Beneficial Uses of Cover Crops. Virginia Cover Crop Fact Sheet Series 1. Virginia Cooperative Extension.
- Magdoff, Fred and Harold van Es. Building Soils for Better Crops, 4th Edition. 2021. Sustainable Agriculture Research and Education (SARE).
- Managing Cover Crops Profitably, 3rd Edition. 2012. Sustainable Agriculture Research and Education (SARE).