Winter Cover Crops 101

As we close to the end of another growing season, it is a good time to look back at the past season, and think about next year’s garden. Did you have too many weeds, still battling heavy clay soils, and felt the battle-of-the-bugs was lost? Me too! If you’re like me, I would have loved to have had a better handle on just one of these problems, but with lack of time, did nothing. So what is my solution for nest year? - A winter cover crop.

Cover crops, not knew to most farmers, have not been well utilized by home gardeners. Cover crops are plants grown to cover the soil during idle periods. Gardeners usually plant cover crops in the fall for winter cover, but some gardeners also use cover crops as part of a summer rotation. In the spring, when cover crops are tilled into the soil, they supply plant nutrients and organic matter. When Cover cropped are turned into the soil they are often referred to as “green manures” Even the smallest garden will benefit from the use of cover crops. They provide a number of advantages to the otherwise wasteful use of space during your garden's off-season. Cover crops can:

1. Control Erosion – Heavy fall and spring rains, along with dry winter winds can carrying away small surface particles off topsoil. A thick stand of a cover crop protects the soil surface from wind and its roots hold soil in place against water.

2. Suppress Weed - Cover crops act as a "living mulch", reducing sunlight from reaching the soil surface and subsequently allowing weed seeds to germinate and grow. Also some grasses, such as annual rye, have alleopathic properties that prevent weed seeds from germinating and suppress weed seedlings around the root zone of the rye.

3. Fix Nitrogen– Legume cover crops, inoculated with their specific rhizobium bacteria, will take nitrogen out of the air (present in the soil) and store it in their plant tissues via nodules on the roots of the legume. When the legumes are turned over in the spring the nitrogen becomes available.

4. Improve Soil structure – Cover crops improve soil tilth, texture, moisture-holding ability, and ease of tillage. Added organic matter will help to develop of a wide range of soil microorganisms and earthworms, and help to retain plant nutrients in the soil.

5. Reduce pest Insects - Cover crops encourage beneficial insect populations, often minimizing need for other insect control measures.

What to Plant?

Success in the growth of cover crops requires proper selection of a cover crop, correct timing of seeding and good management techniques. There are many traditional cover crops to select from, including annual ryegrass, winter rye, winter wheat, oats, white clover, sweet clover, hairy vetch and buckwheat.

There are three basic types of cover crops, Legumes, grasses and other boardleaves. Legumes have the ability to symbiotically associate with certain soil bacteria, rhizobium, that fix atmospheric nitrogen. Normally, no commercial fertilizers are necessary to produce abundant biomass from legumes when compared with grasses. Legumes normally produce organic matter higher in N content than grasses. As a result, organic matter originating from legumes usually decomposes at a faster rate than that from grasses. When planting legume cover crops such as clover, vetch, and soybeans, seeds should be inoculated before planting. Inoculum contains beneficial bacteria that the legume needs to fix nitrogen in the soil. In most cases, these bacteria are not found naturally in the soil

Cereal and grasses can grow quickly, even in cool conditions and usually produce more biomass than legumes under adequate fertility levels. Grasses can be easier to grow than legumes, such as clover, because they germinate more quickly and do not require inoculation. Annual ryegrass is a good choice for small gardens in West Virginia. It comes up in seven days or so, and will be well-established by the time plants go dormant. Winter rye and ryegrass grow in a very dense habit and are much more effective at shading out weeds than oats or small seeded legumes.

Broadleaved plants are more difficult to grow and manage than cereal grains and do not provide the nitrogen-fixing benefits of legumes. Buckwheat is a frost-sensitive broadleaf that is easy to grow in warm weather and does well as a summer cover crop. There is no perfect cover crop. Each will have some drawbacks. Seeding dates should be by mid-October at the latest.

Table 1. Buckwheat and Legumes

Cover Crop	Type	Characteristics	Seeding Rate per Acre	When to Plant
Buckwheat	Summer annual	Tolerates many soil conditions	50 lb	After mid-May
Cowpea	Summer annual	Good green manure crop	30-40 lb	After mid-May
Crimson Clover	Winter annual	Good nitrogen producer	12-20 lb	Late August
Flat Pea	Long-lived perennial	Very competitive, slow to establish, high nitrogen producer	20-25 lb	Late August
Hairy Vetch	Winter annual	High nitrogen producer	25-40 lb	August
Medium Red Clover	Perennial	Tolerant of many soil conditions	10-15 lb	March-May
White Clover	Perennial	Widely adapted, long-lived	5-7 lb	March-May
Yellow-Blossom Sweet Clover	Biennial	Allelopathic, bee pasture	12-15 lb	May

Poole. Terry, E. 2004 “Cover Crops” Extension Agent, Agricultural Science University of Maryland Cooperative Extension

Table 2. Grasses

Cover Crop	Type	Characteristics	Seeding Rate per Acre	When to Plant
Annual Rye Grass	Winter annual	Germinates quickly, competitive	25-35 lb	Mid-August
Cereal Rye	Winter annual	Grows quickly, allelopathic	60-120 lb	October
Spring Oats	Summer annual	Quick growth, suppresses weeds	30-60 lb	March-April
Sorghum/Sudex	Summer annual	Quick growing, allelopathic	30-40 lb	May-June
Winter Wheat	Winter annual	Tall-growing living mulch	60-120 lb	October

Poole. Terry, E. 2004 “Cover Crops” Extension Agent, Agricultural Science University of Maryland Cooperative Extension

What’s the catch?

Like all good things, too mush of it can be a problem. In this case, a cover crop can become a weed crop. This is particularly true if the cover crop is permitted to produce seed. The solution to this problem is to mow or till the cover crop before the seed matures. In the spring more than one mowing may be needed to keep seeds from forming. Also, when the cover crop is mowed, turning it into the soil is much easier when doing it by hand or tiller.

Please note this article is only meant to raise awareness and interest in cover crops and by no means covers this broad topic. For more information please contact the WVU Extension Service.