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Cover Crops and Soil Fertility


By Marvin Fisher

What can cover crops do for your Garden in the summer? Well let’s take a look.

Abundant biomass. In summer, large yields of biomass are typical, especially if you cut the cover crop during its vegetative stage to encourage rapid regrowth. You can work this surplus biomass into the soil or use it as livestock feed, compost fodder or mulch. Although overwintered covers provide those same benefits, summer cover crops yield a wider range of home-produced feeds for poultry and livestock, including cut-and-come-again greens, grains and seeds, and dried cover crops used as hay.

Weed suppression. Summertime is prime weed time, and fast-growing summer cover crops suppress weeds. They’re especially useful for filling that blank spot between early and later crops, space that would otherwise offer a field day for weeds.

Biodiversity boost. Summer covers make greater contributions to biodiversity because insects, birds and amphibians feed and reproduce during the growing season. Biodiversity creates ecological balance that can help mitigate plant diseases and damaging insects.

Let’s consider four summer cover crops that best rise to the challenge of warm summer conditions and offer a broad range of benefits, especially in mixed plantings. Nature will do the work of killing these cover crops at the end of the season: All four are intolerant of frost and will die down into a protective mulch as freezing temperatures set in.


This broadleaf annual’s greatest virtues are extremely rapid growth and profuse flowering. Its greatest limitation, extreme sensitivity to frost, can actually be turned into an advantage. Buckwheat can form a tight canopy within two weeks, outstripping and shading out weeds. Its weed-suppressing prowess offers a responsible alternative to toxic herbicides. Tillage plus back-to-back successions of buckwheat have proved effective at suppressing even tough perennial weeds.

For preventing soil’s exposure to baking sun, buckwheat may be the best of all covers to fill a gap between early and later crops. Plant buckwheat after all danger of frost has passed and make additional plantings anytime, up to 35 days before frost. Buckwheat flowers early (30 days from seed to bloom in my northern Virginia garden) and profusely, encouraging honeybees and other beneficial insects. Increase biomass yield by cutting the crop just before it reaches 25 percent bloom. Regrowth is rapid and a second such cutting may be possible. Plants make good fodder for poultry or rabbits, and chickens love buckwheat seeds: Just toss cut stems with seedheads to your flock.

Buckwheat’s vulnerability to frost makes it a useful “nurse” for fall-planted, cold-tolerant crops, such as alfalfa and winter greens, which are often difficult to germinate in late-summer heat. The quick cover of some buckwheat sown with a winter crop will shade and cool the soil. The cold-hardy crop will grow in buckwheat’s shade until a killing frost mows down the buckwheat, freeing the other plants for a surge of growth before winter dormancy.


Hybrid crosses of forage-type sorghum and sudangrass yield dramatic improvements to soil texture and increases in organic matter. Strains of sorghum-sudangrass grow 5 to 12 feet tall and produce an impressive amount of biomass. Cut back to 6 inches when the crop reaches 4 feet high to stimulate regrowth and encourage deeper, more aggressive root growth for opening compacted soil. The cut stalks make long-lasting mulches.

Plant sorghum-sudangrass about two weeks after the date for planting sweet corn in your area and anytime thereafter until six weeks before frost; it thrives in summer heat. After it’s established, sorghum-sudangrass is highly drought-resistant. If planted tightly — in rows spaced 8 inches apart and seeds at 1.5 inches apart, planted 1 inch deep — sorghum-sudangrass will beat out weed competition. Allelopathic compounds exuded from this crop’s roots will suppress damaging nematodes and inhibit many sprouting weeds and crop seeds. However, this means gardeners should wait six to eight weeks after killing sorghum-sudangrass before sowing another crop in the same spot.

Sorghum-sudangrass makes good livestock forage, though you must not feed your animals young plants (those less than 24 inches high) or those stressed by drought or killed by frost, which may cause prussic acid poisoning. Ducks and geese love the leaves, and goats eat the stalks like candy.


Cowpeas thrive in heat, grow fast and, with taproots reaching almost 8 feet deep, are highly drought-tolerant. They set about 130 to 200 pounds of nitrogen per acre and typically contribute a couple of tons of biomass to replenish soil organic matter. They do well in a wide range of soils, except highly alkaline soil.

Plant cowpeas in thoroughly warmed soil a week or two after your recommended date for planting sweet corn. Make successive plantings up to nine weeks before a killing frost. Treat the seeds with a rhizobial inoculant specific to cowpeas to ensure maximum nitrogen fixation. Tight plantings shade out weeds and conserve moisture, so plant seeds 1 inch deep in rows 6 inches apart (up to 15 inches apart for viny varieties) with seeds 2 inches apart in each row.

Beneficial insects feed on cowpeas’ flowers and “extrafloral nectaries” (nectar-secreting glands near leaf nodes).The green plants make good fodder, which can also be dried for hay. Mature seeds provide feed for poultry and livestock and are a delicious table legume, too. Because a number of varieties set seeds at as early as two months, cowpeas are outstanding candidates to follow spring crops and set nitrogen for heavy-feeding, fall-planted alliums.

D & S Farm and Garden is located at 4738 Gates East Road (44062) 440-693-4632.


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