Work garden soil until loose. Amend with compost, if necessary, to achieve moderately fertile conditions in a well-drained area that receives full sun to partial shade, with a pH of between 5.5 and 6.8. Make shallow trenches with your finger about 1/2-inch deep. Space the trenches 12 to 24 inches apart.
Sow purple top turnip seeds about 1 inch apart in the trenches, four to six weeks before the last frost for harvest in late spring, covering the seeds lightly with soil. Purple top and other turnip varieties grow best in daytime temperatures of 60 to 65 degrees Fahrenheit. You must plant them so that you have 45 to 65 days before daytime temperatures reach 75 degrees Fahrenheit. Alternatively, sow them in late summer for a fall harvest after high temperatures have passed, or in regions with cooler summers, sow them every two weeks through the middle of the summer for a continuous yield.
Thin the young turnip sprouts 4 to 6 inches apart when they are a few inches tall, keeping the hardiest ones.
Mulch the purple top plants with straw to protect the top of the tubers from harsh sun.
Water the purple top turnips regularly to keep the soil continually moist. This assures the fastest growth and most tender tubers. Never let the soil become dry.
Side dress the purple tops with compost halfway through the growing season, which means spreading the compost between the rows next to the plants.
Weed the turnip bed constantly. Roots from weeds may cause small purple top tubers and may encourage pest infestations.
Harvest the purple top turnips when the roots are 3 to 4 inches in diameter and the temperature has not risen above 75 degrees Fahrenheit. Use a garden fork to gently lift them out of the ground, and then shake off excess soil. Cut off the greens and eat them immediately, or freeze them for use later. Store the purple top roots in the in a cool, moist place such as a cellar.
Things You Will Need
Plant purple top turnips with bush beans, southern peas or peas for companion plants.