A young, tender turnip (Brassica rapa) and its tasty leaves add fiber, vitamin C and calcium to the family's diet. Turnips are a cool-weather crop, easy to grow in the home garden. Normally grown as an annual, turnips are actually a biennial. The root and leaves develop through the first growing season, and the following year the plant flowers and sets seed. Gardeners growing heirloom varieties may allow a few turnips to overwinter in U.S. Department of Agriculture plant hardiness zones 2 through 11 so they can harvest the seeds for future crops.
Prepare the Garden Bed
Turnips prefer full sun in moist, well-drained, but cool, garden soil. Remove all vegetation and debris from the garden bed. Rake 2 to 4 inches of compost and well-aged manure over the soil and dig it in to a depth of 12 inches. Turnips thrive in an acidic soil with a pH between 5.5 and 6.8.
Planting the Seeds
Like most root crops, turnips are planted directly in the garden bed; they do not transplant well. Gardeners planning an early crop should plant their turnip seeds two to three weeks before the last frost date. Turnip seeds germinate in two to 14 days in soil temperatures between 40 and 85 degrees Fahrenheit. Turnips are also planted in August for a fall crop, approximately eight to 10 weeks before the first frost date.
Planting, Spacing and Thinning
Plant the seeds 1/2 inch deep and 1 inch apart in rows spaced 12 to 24 inches apart. Keep the soil moist but not waterlogged. Water when the soil is dry to the touch, applying 1 inch of water weekly. When the seedlings are 4 inches tall, use scissors to thin the unneeded seedlings, leaving 3 to 4 inches between the remaining plants.
Keeping Turnips Tender
Turnips that grow slowly develop tough, woody roots. Keep the turnips growing rapidly by watering regularly to keep the soil evenly moist and adding 2 to 4 inches of mulch between the rows. Add a shovelful of compost as a side dressing four weeks after the seedlings appear to provide additional nutrients. Harvest the turnips when they are between 1 and 3 inches in diameter, between 30 and 70 days after planting, depending on the variety.