Colorful and crunchy, the radish is a fast-maturing, easy-to-grow vegetable that prefers cool weather. It is also surprisingly varied. The edible roots may be short and rounded or long and slender; flavor may be sweet, mild, or hot; and colors include red, pink, rose, lavender, purple, black, and white.
Radishes are divided into spring, summer, and winter types.
Spring radishes mature in just three to four weeks from seed. Their crisp texture and mildly pungent flavor result from growing in cool weather. Begin planting two to six weeks before the last frost, and continue until four weeks after it; quality declines with warm weather in late spring. You can also plant them for a fall crop by sowing seed in early fall, four to six weeks before the first frost. And in the Coastal and Tropical South (USDA 9-11), radishes can be grown in winter. Recommended selections include 'Burpee White' (25 days from sowing to harvest; round white roots), 'Cherry Belle' (22 days; round red), 'Cherriette' (24 days; round red), 'Easter Egg II' (25 days; oval roots in mix of lavender, pink, rose, red, white), 'Long Scarlet' (25 days; long, narrow red), and 'Sparkler White Tip' (24 days; round red-and-white).
Summer radishes tolerate heat better than spring types. Plant for harvest in spring, early summer, or fall. The group includes 'French Breakfast' (23 days; oblong red roots with white tip) and 'White Icicle' (25 days; long, slender white roots).
Winter radishes, which require 50 to 60 days to mature, are larger and firmer than spring and summer radishes. Some are rounded; others, including the oriental daikon types, are long and carrot shaped. Roots are crisp and mildly pungent and keep well in storage. They require cool weather at the end of their growing season, so plant them as a fall crop (or as a winter crop in the Coastal and Tropical South). Sow seeds at least four weeks before the first fall frost. If you plant them in spring, they may flower before forming roots. Selections include 'April Cross' (60 days; white daikon type), 'Miyashige' (50 days; white daikon type), 'Red Flame' (24 days; sweet, long, narrow, white-tipped), 'Red Meat' (50 days; pink flesh, green skin), 'Round Black Spanish' (55 days; round, black roots with white flesh), and 'Summer Cross' (50 days; white daikon type). There are also novelties like 'Misato Rose Flesh' (60 days), which is green outside and pink inside; 'Watermelon (55 days; green skin that fades to white and bright red interior); and 'China Rose' (55 days; red outside and white inside).
Like other root crops, radishes need soft, loose soil. If your soil is heavy clay, till in plenty of organic matter or plant in raised beds. Sow spring and summer radishes inches deep in rows spaced 612 inches apart. Sow winter radishes inches deep; space rows 1820 inches apart. Thin plants soon after they emerge, leaving 23 inches between spring and summer radishes and 6 inches between winter radishes. When first true leaves emerge, apply cup of 10-10-10 fertilizer per 10 feet of row. Keep soil evenly moist; excessive or uneven moisture may cause radishes to split or become tough and hot in flavor. Floating row covers placed over developing plants will protect them against flea beetles (which eat the foliage) and root maggots (which eat the roots).
Harvest spring and summer radishes as soon as they reach 1 inches in diameter. ('White Icicle' pushes up out of the ground when it is ready.) Leaving them in longer than this can result in hot-tasting, woody roots. Winter radishes can stay in the ground longer, especially in cool weather. Daikon types can grow 11 feet long with no loss in quality.