Dig the soil to a depth of 6 inches for quick-growing radishes and up to 2 feet for large, sharper-tasting, slower-growing winter types. Space seeds ½ inch deep and 1 inch apart; firm the soil and water gently. Make weekly spring sowings as soon as you can work the soil (4 to 6 weeks before the last expected frost) until early summer; start again in late summer. Sow winter radishes in midsummer for a fall harvest.
Thin seedlings to 2 inches apart, 3 to 6 inches for the larger winter types. Mulch to keep down weeds. For quick growth and the best flavor, water regularly.
Companion Planting for Insect Control
Sow Radishes amid hills of cucumbers and squash to repel cucumber beetles. Plant them near spinach. Radishes attract leafminers away from the spinach. The damage the leafminers do to radish leaves doesn't prevent the radishes from growing nicely underground.
Cabbage maggots are attracted to radishes but seldom ruin a whole crop; for controls, see the Top Ten Garden Insect Pests.
Pull as soon as the roots mature. Oversized radishes often crack and are tough or woody.