Seed Specifications

Ra

dish

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GA

RD

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MG 225 March 1, 2003

Master Master Gardeners Gardeners

JournalJournal

Culture

Minimum germination standard: 80%. Usual seed life: 4 years. Approximately 80 seeds per gram; 28 grams per ounce.

Raphanus sativus

Radishes grow best when sown in spring or late summer so they mature when days are shorter, sunlight is weaker, and temperatures are lower. They quickly become pungent (hot) when the weather gets too warm. Rad-ishes are mainly a cool-weather crop, but there are cultivars suited to a wide range of growing conditions. Some daikon and all over-wintering types are frost-tolerant. The best quality and root shape are obtained when the crop grows and matures at moder-ate temperatures (50 to 65oF) in intermediate to short day lengths.

Spade or till the bed deeply when the soil is on the dry side to avoid making clods. Work the soil to a fine texture 6-10 inches deep to obtain, nicely shaped roots. Soft and sandy soils, rich in humus, are best for radish pro-duction. Work in plenty of organic matter, preferably in the fall. Avoid freshly manured soil or the incorporation of green manure just prior to seeding. Radishes are often planted in raised beds to improve root growth and shape. This method improves soil drainage and allows access to the crop without caus-ing soil compaction. Raised beds are typi-cally 4-foot wide by any convenient length

Start planting spring radishes in April as soon as the soil can be worked. Successive

plantings can be made every 10 to 14 days until mid-June. Additional sowings of spring types can be made between mid-August and mid-September to mature in the cooler, moister days of fall. Spring radishes also can be planted in late winter in a pro-tected cold frame, window box, or container. Winter radishes, grown for storage, are not usually sown until mid to late August. They are slower to develop than spring radishes; and they grow considerably larger, remain crisp longer, are usually more pungent, and hold in the ground or store longer than spring varieties.

Sow seed ½ inch deep, ½ inch apart, in rows 15 to 18 inches apart (space 3 to 4 inches apart in both directions for wide row planting). Days to emergence: 4-11. Opti-mum soil temperature for germination: 55-85oF. Radishes will not germinate when the soil temperature is above 95oF or below 45oF. Germination rate declines sharply when soil temperature falls below 55oF. It is essential to thin promptly. Thin spring va-rieties to 1 to 1 ½ inch between plants. Winter radishes must be thinned to 1 to 4 inches, or farther to allow for proper root development. Dry or crowded conditions will slow growth and make roots hot or pithy.

Radishes belong to the Brassicaceae family (cole crop family). Like other brassicas, rad-ishes contain mustard oils, which give them pungency. Radishes have been cultivated for thousands of years in both China and the Mediterranean area. Radishes were a com-mon food in Egypt before the building of the pyramids and are one of our most ancient culti-vated plants.

Radish leaves are deeply pinnate and form a basal rosette. Most radishes produce flower stalks the second year, after cool temperatures followed by long days initiate bolting. Flower-ing or bolting in annual radishes can occur af-ter roots reach edible size and the plant is ex-posed to warm temperature. With warm

weather the seed stalk may develop so rapidly that no edible root is formed. Roots of globe varieties tend to elongate and develop poor shape in hot weather when the tops also grow taller and larger than in cool weather. Once the plant produces a flower stalk, radish flavor and quality deteriorate.

Radishes may be grown as a cool-season an-nual sown in the spring and early summer, or as a biennial if sown in fall. Small, round types have roots up to 1 inch in diameter; small long types up to 3 inches long. Large forms include oriental types (daikon or mooli), and the large winter radishes. Immature seedpods from some varieties and young seedling leaves are edible raw.

Plants require very low nitrogen levels, so fertilize cautiously. To fertilize, use 4 pounds of 5-10-10 or 2 pounds of 10-10-10 per hundred square feet of gar-den as a preplant fertilizer. Radishes

need moderate amounts of boron, cop-per, manganese, molybdenum, and zinc. The optimum soil pH for radishes is 6.0 to 7.0.

Cultivar Selection

MASTER GARDENERS

Pests

Compiled By John T. Kovatch

Diseases Radishes are almost completely disease-free.

Irrigation Radishes should never be allowed to dry out. In dry weather, water the crop ever week at the rate of 2 gallons/sq yd. Over-watering, however, encourages leaf rather than root development, whereas too little water will produce an overly pun-gent taste..

Fertility

Harvest

Flea beetle damage (pinholes in leaves) can reduce growth rate and thus reduce quality of the radishes. Using row cov-ers such as Reemay or AG-19 has shown to be an effective means of preventing flying insects from laying eggs and feeding on plants. Using a row cover can also reduce root maggot populations. You can reduce the amount of time (and therefore the damage) that root maggots have to invade the radish root by encouraging rapid growth, followed by prompt harvesting. For more information, consult University of Wisconsin -Extension publication A2088, Managing Insects in the Home Vegetable Garden.

Radish cultivars are grouped according to the season in which they will be grown. Cultivars may be classified as spring, summer, or winter radishes. Spring radishes are globe-shaped and bright red. They mature in only 25 to 30 days. Summer radishes are similar to spring radishes but are larger and slower to mature. Summer and winter

radishes require approximately 50 to 60 days to mature. Daikons are a long white Asian type of winter radish. Win-ter radishes favor cool temperatures and short days and are normally grown as a fall crop in Wisconsin. Radish breeders select for taste, bolt resis-tance, disease resistance and appear-ance.

Harvest radishes before roots become too large or cracked. Make multiple sowings for a steady supply throughout the season. Spring radishes may be harvested when roots reach edible size (½ to 1 ½ inch in diameter). Remove the tops as you harvest to keep the roots from wilting. Radishes may be kept 10 to 14 days in the refrigerator if

stored in plastic bags with holes punched for air circulation.

The harvest of winter radishes de-pends upon the variety. Winter rad-ishes, grown for storage, may be lifted and stored in boxes of moist sand in a frost-free place for three or four months.

Providing university research-based horticulture information and educational opportunities

Milwaukee County UW-Extension 932 South 60th Street

West Allis, WI 53214-3346 Phone: (414) 290-2400

Fax: (414) 290-2424 http://milwaukee.uwex.edu

Ozaukee County UW-Extension Box 994

121 West Main Street Port Washington, WI 53074

Phone: (262) 284-8288 http://www.co.ozaukee.wi.us

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