Spring radishes should be planted from as early as the soil can be worked until mid-spring. Make successive plantings of short rows every 10 to 14 days. Plant in spaces between slow-maturing vegetables (such as broccoli and Brussels sprouts) or in areas that will be used later for warm-season crops (peppers, tomatoes and squash). Spring radishes also can be planted in late winter in a protected cold frame, window box or container in the house or on the patio. Later-maturing varieties of radishes (Icicle or French Breakfast) usually withstand heat better than the early maturing varieties and are recommended for late-spring planting for summer harvest. Winter radishes require a much longer time to mature than spring radishes and are planted at the same time as late turnips (usually midsummer to late summer).
Spacing & Depth
Sow seed 1/4 to 1/2 inch deep. Thin spring varieties to 1/2 to 1 inch between plants. Winter radishes must be thinned to 2 to 4 inches, or even farther apart to allow for proper development of their larger roots. On beds, radishes may be broadcast lightly and thinned to stand 2 to 3 inches apart in all directions.
Radishes mature rapidly under favorable conditions and should be checked often for approaching maturity. Harvest should begin as soon as roots reach edible size and should be completed quickly, before heat, pithiness or seeds talks can begin to develop.
Pull radishes when they are of usable size (usually staring when roots are less than 1 inch in diameter) and relatively young. Radishes remain in edible condition for only a short time before they become pithy (spongy) and hot. Proper thinning focuses the harvest and avoids disappointing stragglers that have taken too long to develop.