You will need at least 8 inches of dirt and some sand for planting. Plant about 6 inches apart. Keep your bed weed-free and harvest when tennis ball sized.
Turnip greens are fairly easy to grow. The seeds are small but they ssprout like crazy. I would spread out seeds in the ground about 1/8 of a inch deep. Make sure when they sprout to thin them out. Pick turnips after first light frost.
Plant the turnip seeds in soil that has been raked thoroughly and raised in to rows about 4 inches high. Keep a distance of 12 inches between the planted seeds. Water the seeds so they stay moist until you see sprouts. Thin the rows so they don't over-grow.
Grow turnip greens in well-drained soil in the fall. They need water and to grow fast for tender leaves. Plant greens 6 to 8" apart. Don't mind growing in clumps.