Fill a planting container almost to the top with potting soil. Plant the turnip seeds along the top of the soil, spacing the seeds about 2 inches apart. Cover the seeds with 1/2 inch of soil.
Water the soil evenly immediately after planting the seeds.
Place the container in a location with temperatures ranging from 40 to 75 degrees Fahrenheit. A cool room near a sunny window or a basement room with a grow light would be ideal for growing turnips. Provide about six hours of light in each 24-hour period. Keep the soil evenly moist while the turnips grow.
Thin the turnip seedlings when they reach a height of 4 inches. Pull the weakest ones to leave seedlings spaced about 6 to 8 inches apart in the container. Use the greens from the pulled seedlings salads or other recipes.
Harvest turnips between one and two months after sowing the seeds. Pull the turnip roots from the soil whey they are between 2 and 3 inches in diameter. Loosen the potting soil gently around the turnips with a hand rake or trowel and grasp the greens firmly in your hands to lift the turnips.