Plant radishes from seed in the spring as soon as you can dig and till the soil. Till the soil -- in an area with full sun -- about 8 inches deep and work in approximately 3 inches of peat moss, compost or another type of organic matter. Plant seeds 1/4 inch deep, spaced 1 inch apart. Water them in with 1/2 inch of water.
Thin seedlings to one every 4 inches. Continue to keep the soil moist and the garden weed free. Let the radish tops die back to the ground in the fall. The roots are still alive.
Begin to water the radishes and keep the garden weed free the next spring when they start to grow again. They will bloom the second summer. Since radishes are biennials, they will die after the weather cools.