The radish (Raphanus sativus or Raphanus raphanistrum subsp. sativus) is a flowering plant in the mustard family, Brassicaceae. Its large taproot is commonly used as a root vegetable, although the entire plant is edible and its leaves are sometimes used as a leaf vegetable. Domesticated in Asia, radishes are grown and consumed globally. The radish is sometimes considered to form a species complex with the wild radish and instead treated as the subspecies Raphanus raphanistrum subsp. sativus. Radishes are often used raw as a crunchy salad vegetable with a pungent, slightly spicy flavor, varying in intensity depending on its growing environment. There are numerous varieties varying in size, flavor, color and length of time they take to mature. Radishes owe their sharp flavor to the various chemical compounds produced by the plants, including glucosinolate, myrosinase, and isothiocyanate. They are sometimes grown as companion plants and suffer from few pests and diseases. They germinate quickly and grow rapidly, common smaller varieties being ready for consumption within a month, while larger daikon varieties take several weeks. Being relatively easy to grow and quick to harvest, radishes are often planted by novice gardeners. Another use of radish is as a cover or catch crop in winter or as a forage crop. Some radishes are grown for their seeds; others, such as daikon, may be grown for oil production. Others are used for sprouting.
Description
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. The roots obtain their color from anthocyanins. Red varieties use the anthocyanin pelargonidin as a pigment, and purple cultivars obtain their color from cyanidin. Smaller types have a few leaves about 13 centimetres (5 inches) 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). Radishes harvested at the proper time are crisp and mild but become bitter and tough if 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. The radish is a diploid species, and has 18 chromosomes (2n=18). It is estimated that the radish genome contains between 526 and 574 Mb.
Varieties
Origins Varieties of radish are now broadly distributed globally, but almost no archeological records are available to help determine their early history and domestication. However, scientists have tentatively located the origin of Raphanus sativus in Southeast Asia, as this is the only region where truly wild forms have been discovered. South Asia, Central China, and Central Asia appear to have been secondary centers where differing forms were developed. Radishes enter the historical record in third century BC. Greek and Roman agriculturalists of the first century AD gave details of small, large, round, long, mild, and sharp varieties. The radish seems to have been one of the first European crops introduced to the Americas. A German botanist reported radishes of 45 kilograms (100 pounds) and roughly 90 cm (3 feet) in length in 1544, although the only variety of that size today is the Japanese Sakurajima radish. The large, mild, and white East Asian form was developed in China, though it is mostly associated in the West with the Japanese daikon, owing to Japanese agricultural development and larger exports.
Cultivation
Radishes are a fast-growing, annual, cool-season crop. The seed germinates in three to four days in moist conditions with soil temperatures between 18 and 29 °C (65 and 85 °F). Best quality roots are obtained under moderate day lengths with air temperatures in the range 10 to 18 °C (50 to 65 °F). Under average conditions, the crop matures in 3–4 weeks, but in colder weather, 6–7 weeks may be required. Homegrown varieties can be significantly sharper. 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 (1⁄2 in) deep recommended for small radishes to 4 cm (1+1⁄2 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%.
Companion plant 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 also 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.
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