Ron and Jennifer Kujawski: Improving Soil with Cover Crops

Cover crops can do wonders for next year’s garden. So how do you decide which to plant?

Oats used as cover crop grow between rows of maize. Photo © Alan Manson, via Wikimedia Commons

Planting a cover crop is a great way to improve garden soil during the times when it’s not actively involved in vegetable production; cover crops prevent soil loss from erosion, as well as returning organic matter to the soil. Cover crops are also effective during the growing season to control weeds, reduce soil compaction, and take up any excess nutrients crops don’t use. You can also plant low-growing cover crops like clover between rows of vegetables and in paths.

In our own garden, we like to experiment with different cover crops and have had success with oats and winter rye in fall, as well as buckwheat, Sudan grass, and berseem clover in summer. Following are some common cover crops you might try:

Grasses

Winter rye (Secale cereale)

Seeding time and rate: Late summer to mid-October at 2 – 3 lbs/1,000 square feet
Cut/kill method: Mow in spring before seeds set (if extensive growth) and till under
Benefits and tips:

• Germinates at low temperatures and can be planted later than other cover crops
• Cold hardy and tolerant of low-fertility soils
• Produces a lot of growth in spring
• May prevent weed-seed germination, but can also affect tiny vegetable seeds if tilled in spring too close to planting time

Oats (Avena sativa)

Seeding time and rate: Mid-August to mid-September at 1 – 2 lbs/1,000 square feet
Cut/kill method: Till under in spring
Benefits and tips:

• Fast-growing cover
• Tolerant of wet soils
• Winter killed

Sorghum-Sudan-grass (Sorghum bicolor × S. sudanense)

Seeding time and rate: Late spring to midsummer at 1 lb/1,000 square feet
Cut/kill method: Mow during summer if needed and till under in spring or transplant vegetable seedlings into winter-killed grass
Benefits and tips:

• Fast growing, but requires good fertility and moisture
• Excellent weed control 
• Winter killed

Legumes

Hairy vetch (Vicia villosa)

Seeding time and rate: August to early September at 1– 2 lbs/1,000 square feet
Cut/kill method: Cut in spring and till under or cut at flowering and till under
Benefits and tips:

• Best nitrogen-fixing legume
• Produces substantial growth
• Mix with vetch/pea inoculant before sowing 
in new areas
• Winter hardy
• Can be sown with rye or oats

Crimson clover (Trifolium incarnatum)

Seeding time and rate: Late summer to early fall at 0.5 – 2 lbs/1,000 square feet
Cut/kill method: Till under in spring
Benefits and tips:

• Adds nitrogen to soil
• Not reliably winter hardy
• Can also be spring planted and grown as summer cover crop
• Use true clover inoculant before sowing in new areas

Cowpea (Vigna sinensa)

Seeding time and rate: Early summer to late summer at 2 – 3 lbs/1,000 square feet
Cut/kill method: Till under at flowering or if late planting, allow to winter-kill
Benefits and tips:

• Adds nitrogen to soil
• Develops deep taproot and is tolerant of droughty, poor soil once established
• Good for summer weed control
• Winter killed
• Use cowpea/peanut inoculant before sowing in new areas

Other

Buckwheat (Fagopyrum esculentum)

Seeding time and rate: Early summer to midsummer at 3 lbs/1,000 square feet
Cut/kill method: Mow and/or till under at flowering
Benefits and tips:

• Fast growing, can get two crops in summer if allowed to reseed
• Good for summer weed control
• Tolerates acid soil
• Winter killed

Text excerpted from Week-by-Week Vegetable Gardener’s Handbook © 2010 by Ron Kujawski and Jennifer Kujawski. All rights reserved.