University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article


Dr. Leonard Perry, Extension Professor
University of Vermont

 A cover crop is just that-- a crop sown to cover a fallow garden area.  There are many choices, depending on the purpose.

While growing, cover crops can slow soil erosion, outcompete weeds, provide cover over the ground so no light reaches it and so no weed seeds germinate, and to help air and water permeate the soil.  By reducing soil compaction, they increase water infiltration.  This in turns reduces run-off of nutrients into waterways. Cover crops increase the diversity of plant species, helping beneficial insects and microorganisms.

Some legume (pea family) crops such as hairy vetch, clovers, and Fava beans also add nitrogen. They have special bacteria on their roots that take nitrogen from the air, and convert it to a nitrate form that plants can then use. Such legumes should be plowed under before they bloom.

When you till the crops under, they add organic matter to the soil.  This improves soil structure and fertility, recycling nutrients back into the soil.

Most cover crops are perennial, but buckwheat is an annual.  Sow it in early summer, with 2 to 3 pounds per 1000 square feet.  It grows rapidly, especially in heat, reaching 2 or 3 feet high. Use it to control weeds and erosion, then till into the soil in late summer.

Another annual crop, annual or Italian rye, is also used to control weeds.  Sow in spring, or even the fall prior, with 2 to 3 pounds per 1000 square feet.  Then till into the soil in fall or even the following spring.

Red, crimson, and berseem clovers are summer cover crops to control weeds.  Sow either in spring or early fall, with 2 to 3 pounds per 1000 square feet.  You can then till into the soil in late fall while still green (a "green manure" crop), or leave overwinter and till in the next spring.  Mowing first before tilling is easiest.  Clovers are legumes, so also add some nitrogen to the soil.

Alfalfa is also used to add nitrogen to the soil.  It is also a long term cover crop to provide ground cover and control erosion.  Sow with 2 to 3 pounds per 1000 square feet in fall or spring, and leave for two years before tilling into the soil.

Another crop to add nitrogen to the soil is hairy vetch.  It is also drought tolerant.  Sow in spring or fall with 2 to 4 pounds per 1000 square feet.  Then till into the soil in fall if sown the previous fall or spring.  A spring sowing may be left overwinter and tilled in the following spring.

Oats are used to control weeds, and as a winter cover crop.  Depending on desired use, sow in spring and till in during fall for the former.  For the latter use, sow in late summer or early fall and till in the following spring.  Use 4 to 5 pounds per 1000 square feet when sowing.  For small gardens, use 4 ounces per 100 square feet.  Since oats are winter killed, plant early for the most growth before frost.

Combine oats or rye with hairy vetch for the benefits of both.  Sow 5 pounds of this mix per 1000 square feet in spring, then till in during fall.  You may sow such crops in fall, then till in the following spring or plant directly in the residue without tilling.

If you want a winter cover crop, but are like me and don't get around to sowing one in late summer, consider winter rye.  It can be seeded later than most others, into early fall, with 4 to 5 pounds per 1000 square feet.  Then till in the following spring.  Like the hairy vetch, this one is also drought tolerant.

If you have the space, it is best to rotate your garden to a different area every year or two.  This gives the previous beds a rest, and allows you to leave them for a season with a cover crop.  This will help replenish soil structure and fertility, keeping weeds under control, and result in better gardens back there the following year.

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