Multiple Purpose Cover Crops

By Bill Duesing

There are numerous good reasons to plant cover crops in your garden or on your farm. And fall is the ideal time to plant cover crops.

These crops, also called green manures, grains, legumes or forage crops, provide a wide range of benefits including:

• Great beauty

• Beneficial soil covering to control erosion

• Better understanding of the two-way relationship between plants and soil organisms

• Weed suppression

• Healthy habitat for pollinators and other beneficial organisms

• Nitrogen production

• Compaction control, breaking up hard pan

• Pest management

• Green manure for added soil nutrients

•   Food for insects, animals and people

•   Biomass (organic matter)

•   Seeds for subsequent cover crops

•   A good way to get more carbon into the soil

Winter Rye

Winter rye and hairy vetch are often sown together in late summer.  They both survive the winter and produce lots of biomass in the spring.  In addition, the rye helps suppress weeds. New techniques using a roller-crimper are able to turn these vigorous crops into a thick mulch.

Winter rye is the best known cover crop. It is an annual grain crop that can be planted most anytime in the next several months. It grows quickly, stays green all winter and starts growing again in the late winter. Throughout the winter, winter rye protects the soil against erosion, and when it photosynthesizes, it sends nutrients to feed soil organisms. (Plants feed soil organisms. Soil organisms feed plants.) Winter rye also has an allopathic effect which helps control weeds.

In mid-to-late spring, rye will be a thick stand of grass about a foot or so tall.  Rye is most often turned into the soil, after mowing, at this time to prepare for planting the next crop. However, its extensive root system (a benefit for soil organisms and organic matter) makes this difficult without serious tillage equipment or a good back and shovel. I've had success mowing it and then digging a furrow through it for planting a crop such as potatoes, while leaving the rest as a ground covering between the rows. 

In late May or June, rye starts to go to seed.  If it is cut after that, it will stop growing taller but remain green.  It is then easy to place larger plants into it (tomatoes or squash for example).  If rye is cut after it is between five or six feet tall and left in place, the straw provides a great ground covering mulch for pumpkins or squash.

By July the rye is six to seven feet tall, a golden color with heads full of rye seeds. The seed can be harvested for baking or eating (if you are so inclined and careful to avoid the ergot fungus that rye is susceptible to) or for planting several months later. That leaves a lot of wonderful straw, those six foot tall dried stems made of slow-to-break-down, carbon-rich fiber that is perfect for mulching, animal bedding or making compost. (John Jeavons, author of the classic How to Grow More Vegetables, recommends planting about three quarters of your growing area to compost crops that can provide grains for food and stems for compost.)

Other cover crops

It is advisable to use other cover crops (besides winter rye) throughout the year.  This helpful chart can get you started. It lists 28 farm seed crops with information about planting times, requisite soil temperatures, hardiness, growth rate, planting depth and the amount to plant per 1,000 square feet or acre.  The chart also indicates the benefits of each crop. 

Here are some of my favorite cover crops used on our Old Solar Farm over the years.

Clovers

Mammoth red clover.

Mammoth red is the best clover for poor soils. It is very cold tolerant and can fix up to 70 to 110 pounds of nitrogen per acre. It also is deep rooted so it loosens soils and brings nutrients to the surface. Like all of the nitrogen-fixing legumes, it does best if it is inoculated with the appropriate species of nitrogen-fixing bacteria before planting. Red clover attracts bees and hummingbirds. Its flowers make a healthy tea.  I frequently leave a few of these plants in the beds or rows. For several years I've been experimenting with red clover mixed in the strawberry patch. We'll see how that works.

There is also a medium red clover that is lower growing and can be cut for hay or silage.  It also can be grown between rows of vegetables if it is mowed. This clover can fix up to 150 pounds of nitrogen per acre, or over three pounds per 1,000 square feet!

Crimson clover has beautiful dark flowers. A winter annual, it is treated like winter rye-planted in late summer.  It starts flowering the following May before dying back.

White clover.

New Zealand, Dutch or other varieties of white clover are likely the best known of the clovers. They withstand traffic and close mowing. As a result, they are often used between vegetable rows or beds.  Before America began the destructive practice of using chemical fertilizers and herbicides on our lawns, white clover was an important ingredient in a lawn seed mix. It provides needed nitrogen and a deep green color all season long.

The author next to a seven foot tall white sweet clover plant. This plant is its second year when it provides one of the best sources of honey. Its deep roots break up compacted soil. It also fixes nitrogen, controls erosion, suppresses weeds and  provides green manure, forage and biomass. Notice seeds along the stems which can be collected for planting. There is also a yellow flowering variety.

Sweet clover is a very tall biennial that is the source of clover honey.  See the caption above for more information.

Hairy Vetch

For beauty it is hard to beat hairy vetch with its abundant and beautiful bluish purple flowers. As a legume, it fixes nitrogen. It climbs up any nearby plant or post with stems five or more feet long. Although it can occupy a lot of space, it has a small and easy to break connection with the soil. At the Rodale Farm they use a roller-crimper on the front of a tractor to kill the vetch and turn it into a thick mulch. A planter on the back of the tractor drops corn seed into a slit it's made through the vetch. That cover crop provides both nitrogen and weed control. No chemical fertilizers or herbicides needed.

Hairy vetch was growing in many places on our farm this year. I was many times stopped by its beauty. Hairy vetch can be planted anytime, but is most often planted in late summer. It fixes nitrogen and the next spring and summer its stunning purple flowers feed bees. 

At Rodale farm they use a roller crimper to turn hairy vetch into a nitrogen rich, weed inhibiting  mulch for corn which is planted by a slit seeder in the same pass as the rolling and crimping operation.

Buckwheat

A quick growing crop that can suppress weeds and feed the bees.

Buckwheat is a beautiful, quick-growing crop that is frost sensitive. It can be tilled in after about a month of growth. This is important if you don't want it to set seeds, which could be weeds in some crops. However, I like to let it flower because of its beauty and the great variety of insects, including honey bees, which feed on its flowers. It is not a sturdy plant, so is easy to get rid of if you don't want it.

Forage Radish

Forage radish in bloom.

This is a daikon radish selected for its ability to penetrate hard pan soils and extract nutrients. Forage radishes are planted in the late summer and are eventually killed by several consecutive nights with temperatures in the low 20s. It is a daikon, so we harvest some for eating. Others we let go to seed for collecting and planting the next year. If left in the ground, the roots decompose over the winter leaving water holding holes, a good thing.

Oats

Oats are another good cover crop grain. If planted in mid-August, it will grow into a dense grass that lives through the first frosts before the really cold winter weather kills it. Then it is a good thick covering for the soil in winter which is easier to plant into than winter rye. It can also be planted in spring for early incorporation into the soil or for grain.

Cover Crop Cocktails

Winter rye and hairy vetch is a classic winter cover crop. The vetch keeps flowering after the rye has set its seeds.

Many farmers are now using cover crop cocktails which combine the benefits of many of these crops for the soil and environment. Johnny's Selected Seeds sells spring and fall green manure mixes. The spring mix includes field peas, oats and hairy vetch, to provide nitrogen, organic matter and weed suppression. Their fall mix includes winter rye, field peas, ryegrass, crimson clover and hairy vetch. Any time you plant legumes, the seed should be mixed with an appropriate inoculant before planting.

Fedco sells a PVO soil building mix which includes field peas, hairy vetch and oats. The oats grow first, and are pulled down by the climbing peas before the whole is covered by the smothering vetch. This combination can produce four tons of organic matter per acre which is disked in or mowed and incorporated in the fall.

Now, as the leaves begin to turn and the days get shorter, consider planting some or all of these beneficial crops on ground that is bare or will be bare soon. Good planting to you!