Early radish varieties usually grow best in the cool days of early spring, but later-maturing varieties can be planted for summer use. One variety — French Breakfast — holds up better than a lot of the early types in summer heat if water is supplied regularly. Additional sowing of spring types can begin in late summer, to mature in the cooler, moister days of fall. Here are some good spring varieties to try:
Burpee white (25 days to harvest, round, smooth white skin). Champion, (28 days, large, red and round). Cherry Belle (22 days, round, red). Cherry Queen Hybrid (24 days, deep red, round, slow to become pithy). Early Scarlet Globe (23 days, globe shaped, small taproot, bright red). Easter Egg (25 days, large, oval, color mix includes reddish purple, lavender, pink, rose, scarlet, and white. For spring and summer use, the best types seem to be the French Breakfast and the Icicle.
Spring radishes should be planted as early as the soil can be tilled until mid-spring. Make successive plantings of short rows every 10-14 days. Plant in spaces between slow-growing vegetables such as broccoli and brussel sprouts. You can also put them in areas where you are waiting until it warms up to plant the peppers, tomatoes and squash. Spring radishes could also be planted earlier if you have a cold frame.
Winter radishes must be thinned to two to four 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 two-three 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 seed stalks begin to develop. Harvest radishes when they are about less than one inch in diameter and pretty young. Radishes remain edible for only a short time before they become pithy (or spongy) and hot. Proper thinning focuses the harvest and avoids disappointing stragglers that have taken too long to develop. Winter varieties mature more slowly and can be harvested when they are larger in size. Once they reach maturity, they can keep their good quality for a longer time, especially in the cooler fall. Buy extra seed in the spring if you plan to have late radishes because it’s hard to find radish seed in August. The Daikon, or Chinese radish, can achieve particularly large size and still maintain excellent quality. Winter radishes can be pulled up before the ground freezes and stored in moist cold storage for up to several months. Several things could cause your radishes to have all tops and no roots. The seeds may have been planted too thickly.