Radish (Raphanus raphanistrum)

Description

Raphanus sativus, commonly called the radishes, have had a long relationship with man. Southern Asia is believed to be the country of origin since truly wild forms have been found there. Middle Asia and India appear to be secondary centers where many different forms developed subsequently. Third-century B.C. Greeks wrote of their radishes, and by 100 A.D., Roman writers described small and large types, mild and biting varieties, and round and long forms. A German botanist in 1544 reported radishes of 100 pounds. Radishes appear to be one of the first European crops introduced into the Americas, closely behind the arrival of Columbus. The white daikon (“big root” in Japanese) is common in Japan, and gardeners in increasing numbers are growing it here. The daikon has a milder, sweeter flavor than ordinary radishes. The root shape of all varieties is either long and cylindrical or short and round. The cylindrical roots range from 6" to 2' long and are either tapered or blunt at the end. The round varieties are the size of a baseball. Radishes are annual or biennial brassicaceous crops grown for their swollen tap roots which can be globular, tapering, or cylindrical. The root skin colour ranges from white through pink, red, purple, yellow, and green to black, but the flesh is usually white. Smaller types have a few leaves about 13 cm (5 in) long with round roots up to 2.5 cm (1 in) in diameter or more slender, long roots up to 7 cm (3 in) long. Both of these are normally eaten raw in salads. A longer root form, including oriental radishes, daikon or mooli, and winter radishes, grows up to 60 cm (24 in) long with foliage about 60 cm (24 in) high with a spread of 45 cm (18 in). The flesh of radishes harvested timely is crisp and sweet, but becomes bitter and tough if the vegetable is left in the ground too long. Leaves are arranged in a rosette. They have a lyrate shape, meaning they are divided pinnately with an enlarged terminal lobe and smaller lateral lobes. The white flowers are borne on a racemose inflorescence. The fruits are small pods which can be eaten when young. Radishes are a fast-growing, annual, cool-season crop. The seed germinates in three to four days in moist conditions with soil temperatures between 65 and 85 °F (18 and 29 °C). Best quality roots are obtained under moderate day lengths with air temperatures in the range 50 to 65 °F (10 to 18 °C). Under average conditions, the crop matures in 3–4 weeks, but in colder weather, 6–7 weeks may be required. Radishes grow best in full sun in light, sandy loams, with a soil pH 6.5 to 7.0, but for late-season crops, a clayey-loam is ideal. Soils that bake dry and form a crust in dry weather are unsuitable and can impair germination. Harvesting periods can be extended by making repeat plantings, spaced a week or two apart. In warmer climates, radishes are normally planted in the autumn. The depth at which seeds are planted affects the size of the root, from 1 cm (0.4 in) deep recommended for small radishes to 4 cm (1.6 in) for large radishes. During the growing period, the crop needs to be thinned and weeds controlled, and irrigation may be required. Radishes are a common garden crop in many parts of the world, and the fast harvest cycle makes them particularly suitable for children's gardens. After harvesting, radishes can be stored without loss of quality for two or three days at room temperature, and about two months at 0 °C (32 °F) with a relative humidity of 90–95%. Radishes can be useful as companion plants for many other crops, probably because their pungent odour deters such insect pests as aphids, cucumber beetles, tomato hornworms, squash bugs, and ants. They can function as a trap crop, luring insect pests away from the main crop. Cucumbers and radishes seem to thrive when grown in close association with each other, and radishes also grow well with chervil, lettuce, peas, and nasturtiums. However, they react adversely to growing in close association with hyssop.