Cover crops can protect the soil from erosion, add nitrogen to the soil and add organic matter to the soil. Winter cover crops useful for Cabarrus County include crimson clover, red clover, and annual rye.
During the winter clovers make a good choice for a cover crop. Crimson clover and red clover both can be planted in September. The crimson clover seems to have more bulk but the nitrogen fixation for red clover is listed at 114 pounds of nitrogen per acre compared to 94 lbs. per acre for crimson clover. Once disadvantage of planting these legumes is that most of the nitrogen fixation occurs in late April and early May. Crimson clover does even better if allowed to go until the end of May. A lot of the biomass is formed this time of the year.
If the clover is plowed down for an early garden, there is not much benefit. Crimson clover is recommended at 1/2 lbs. per 1000 square feet. Red clover can be seeded at 1/4 lb. per 1000 square feet.
Clovers come up best when planted in soil that has been limed recently.
Trying to get a plant that fixes nitrogen earlier has lead some people to try hairy vetch.
I think hairy vetch has the potential to become weedy in my garden so I have avoided it so far.
Austrian winter peas are another choice for winter cover. Austrian winter peas are not recommended as reliable a crop for the piedmont, but I know several people in Cabarrus county growing Austrian winter peas for deer feed. They have the potential to fix more nitrogen but again this is in May.
Annual rye is another winter crop. Choose rye when you need something besides a legume in the rotation or when you have adequate nitrogen. The seeding rate is around one lb. of rye for every 1000 square feet.
Rye can give more forage than any of the other small grains. Oats, barley or wheat could be grown as a cover crop but I don't see any advantage of these grains over rye for an average home gardener.
Mixing the clover and rye is a possibility to get advantages from both. You can get organic matter from the rye and nitrogen fixation from the clover. I have never personally tried a mixture but have seen it work for others. This mixture can be hard to turn under. Since you are planting a mixture cut back on the seeding rate for each crop.
Rye is different from ryegrass. My tendency is to stay away from ryegrass because it can become a weed. Perennial ryegrass seems to be worse as a weed. Ryegrass is also hard to work down and hard to kill. It may be a crop of choice for some types of no till were you kill it down with Round-up. Otherwise, I would steer clear of it.
Some people are planting brassicas as cover crops. The brassicas include all the greens like turnips and kale. There are several forage brassicas. They are not grown by the livestock farmers in our area, because the cows don't like the taste. The reason gardeners might want to grow them is that they produce more organic matter than turnips or other edible brassicas.
The disadvantage is the fact that seed has to be ordered. I would suggest using a readily available seed like turnips. I generally have part of my garden planted in turnips through the fall. Turnip roots have a good amount of organic matter. In fact, I have had trouble disking them under. It is possible to get brassicas to produce the same chemical available in a herbicide called basimid. Basimid can give excellent results but I haven't seen any research on how effective brassica cover crops might be.
The other thing I have done is to use weed seeds that are present in the soil as a green cover crop. By disking on a regular basis you can reduce the number of weed seeds as well as turn under lots of organic matter. On the negative side, you can also ruin the structure of the soil if you till too much or till without lots of green weeds. If you run short on weed seed during the summer, you can add some buckwheat so you can keep tilling in organic matter.
During the winter the ground is normally too wet to turn under the weeds.
Native weeds can still help in the winter. In the part of the garden that isn't in turnips, there are several winter weeds that have grown well most years. One of these was chickweed although that one didn't do too well this past year. I think the reason that the chickweed didn't do very well this past year was because I have finally got enough lime in the soil. So this year I will be growing some clover in parts of the garden.
Article was written by David Goforth Agriculture Extension agent North Carolina Cooperative Extension Cabarrus County Center. Visit my homepage http://cabarrus.ces.ncsu.edu/ or http://cabarrus.ces.ncsu.edu/index.php?page=lawngarden or my blog http://gardeninggurugoforth.blogspot.com/
Contact me at David_Goforth@ncsu.edu. Reviewed 2007.