Green manures are created when a gardener plants a certain type of nutrient-rich crop, and mixes the plants into the soil bed to enrich the garden soil. The practice of making green manure is also called planting cover crops, or break crops. Most cover crops are types of grasses or legumes, such as clovers, ryegrasses, wheat and buckwheat. Red clover (Trifolium pratense) is a good choice for a cover or green manure crop, because its roots improve the soil structure, and the plant can deliver organic matter and large amounts of nutrients to the soil.
Prepare the soil bed by removing all weeds, grasses and other debris. Loosen the soil until it achieves a finer texture using a rototiller, and then firm down the soil using a roller and level the seed bed. You can plant the red clover between April and August, either prior to, in place of or after the harvest of your summer crops.
Plant the red clover seeds 1/3- to ½-inch deep into the soil at a rate of 13 to 18 pounds per 1 acre, or at a rate of 1 to 4 ounces of seed per 100 square feet for smaller areas. Plant the seeds using a slit-seeder, seed spreader or strip-seeder.
Weed the red clover bed by hand-pulling any weeds that emerge. Red clover cannot compete very well with weeds.
Begin topping the red clover after the plants begin to grow tall and crowded. Mow the red clover about four to six weeks before the first frost in fall if you planted the clover in autumn, preferably after the clover begins to bloom but before they go to seed.
Turn the red clover into the soil bed and mix the plant materials into the soil using a pitchfork and/or a rototiller. Wait about three weeks before planting the next crop to allow the plant materials to decompose.