Cover crops come in many forms. There are annual and perennial cover crops. They range from several-inch-tall clover to seven-to twelve-foot-tall Sudan grass. To choose a crop, think about how long you can spare the space, or what time of year it is, as well as the strengths and limitation of each option.
Buckwheat (Fagopyrum esculentum) is an excellent annual cover crop with allelopathic attributes. This means that buckwheat releases chemicals into the soil that discourage the germination of weed seeds. The bees in your neighborhood will also appreciate buckwheat when it’s in bloom. That said, it is quick to bloom and set seed. If you want a continuous crop of buckwheat, this can work out, but if you have other plans, you will need to plow your crop under before seeds form.
Oats (Avena sativa) die in winter, making it a good choice when you need a fast-growing cover crop that you don’t want to have to plow under when spring arrives.
Rye (Lolium multiflorum) is a sturdy cover crop that lasts a long season, but winter temperatures won’t kill it, so it must be plowed in well ahead of spring planting.
Sudan grass (Sorghum bicolor) provides excellent biomass and it dies over the winter, but even so it may generate more material than which home gardeners can cope (without access to tractors). The best way to handle Sudan grass on a small scale might be to mow it first than till or shovel in what remains.
Legumes, such as small-seeded fava beans, cow peas and soybeans also make excellent nitrogen-fixing cover crops. The use of nitrogen-fixing innoculants increases their contributions.