Clover (Trifolium spp.) is called nitrogen fixing because it hosts bacteria nodules in its roots that yield nitrogen that nearby plants can use. When clover dies, this nitrogen becomes useful to vegetables and flowers. Because of this, clover is sometimes called "green manure," making it useful as a cover plant in gardens, and it can also be planted for turf. The timing of sowing depends on its use.
General Planting Time
Plant clover in the spring when frost has past and temperature is 40 degrees Fahrenheit or warmer at night. The best time to plant clover in the spring is from mid-April to mid-May to coincide with spring rains. Clover needs about 30 inches of rain, ideally at least 45 inches, and from four to six hours of sunlight daily. If you are able to irrigate, seed clover in late summer to early autumn. If you plant it then, do it at least six weeks before the first heavy freeze. If freezing temperatures are rare in your climate, you can plan it any time in the winter. Dutch white clover )Trifolium repens) will grow in U.S. Department of Agriculture plant hardiness zones 4a through 9b. Red clover (Trifolium pretense) will grow in USDA plant hardiness zones 3a through 8b.
Planting as Garden Cover
As a living mulch, clover not only contributes nitrogen to the soil, it keeps weeds at bay and holds moisture in the soil. If you plant clover between rows of vegetables, sow it one-third of the way through the growing cycle of the vegetables. If the clover is already growing, dig rows in it for pole beans or dig holes for broccoli, tomatoes, eggplants or other tall-growing vegetables.
Planting as Turf
Dutch white clover is often mixed with grass seed for lawns in spring planting because it will grow in areas that are too shady or poorly drained for conventional grass species. Clover spreads rapidly, crowding out broadleaf weeds that appear in lawns, plus it resists drought, remaining green in dry, hot summer weather. This spreading quality give some annual species invasive qualities. These include the narrow-leaved clover (Trifolium angustifolium), shamrock clover (Trifolium dubium), knotted clover (Trifolium striatum) and subterranean clover (Trifolium subterraneum).
Clover Planting Basics
Clover needs soil with a pH between 6 to 7. Spread 2 ounces of tiny clover seeds on top of 1,000 square feet. Mixing the seeds with sand makes them easier to spread. Rake the seeds lightly into the soil and rake no more than 1/4 inch deep. Water newly sown seeds occasionally to keep the soil moist. When temperatures are warm, clover seeds will germinate in seven to 15 days. Clover grows from 6 to 8 inches tall. If you mix clover seeds with lawn grass seeds, they should be 5 to 10 percent of the total seed weight. There is no need to fertilize.