In an area with full sun, loosen the soil to 12 inches, work an organic fertilizer into the soil, and sow the turnip seeds approximately two to three weeks before the last expected frost date of the region or in early spring. Turnips grow well in weed-free gardens with slightly damp soil and in temperatures that range from 40 to 75 F. Harvest the turnips 30 to 60 days after planting.
Sow turnip seeds directly in the garden after adding a 2- to 4-inch layer of mulch and tilling the mulch into the soil to allow for adequate drainage. Plant the seeds as soon as the ground thaws in early spring by scattering the seeds onto the ground then covering the seeds with up to 1/2 inch of soil.
Thin the seedlings to one plant every 6 inches when the plants reach 4 inches tall. Do not thin the seedlings when growing turnip greens. Provide the plants with 1 inch of water each week. To reduce weeds and prevent sunburn on the turnip tops, place a thick layer of mulch over the established seedlings. When the main plant stalks are 2 to 3 inches in diameter, lift the turnips out of the ground with a gardening fork.