The radish (Raphanus sativus) is an edible root vegetable of the Brassicaceae family that was domesticated in Europe in pre-Roman times. Radishes are grown and consumed throughout the world, being mostly eaten raw as a crunchy salad vegetable. They have numerous varieties, varying in size, flavor, color, and length of time they take to mature. Radishes of spicy varieties 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, smaller varieties being ready for consumption within a month, while larger daikon varieties take several months. Another use of radish is as cover or catch crop in winter or as a forage crop. Some radishes are grown for their seeds; daikon, for instance, may be grown for oil production. Others are used for sprouting and both roots and leaves are sometimes served cooked.
Varieties of radish are now broadly distributed around the world, but almost no archeological records are available to help determine their early history and domestication. However, scientists tentatively locate the origin of Raphanus sativus in southeast Asia, as this is the only region where truly wild forms have been discovered. India, 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 100 lb (45 kg) and roughly 3 ft 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, but is mostly associated in the West with the Japanese daikon, owing to Japanese agricultural development and larger exports.
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.
The radish is a diploid species, and has 18 chromosomes (2n=18).
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 the United States, and the fast harvest cycle makes them a popular choice 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.
As a fast-growing plant, diseases are not generally a problem with radishes, but some insect pests can be a nuisance. The larvae of flea beetles (Delia radicum) live in the soil, but the adult beetles cause damage to the crop, biting small "shot holes" in the leaves, especially of seedlings. The swede midge (Contarinia nasturtii) attacks the foliage and growing tip of the plant and causes distortion, multiple (or no) growing tips, and swollen or crinkled leaves and stems. The larvae of the cabbage root fly sometimes attack the roots. The foliage droops and becomes discoloured, and small, white maggots tunnel through the root, making it unattractive or inedible.
Broadly speaking, radishes can be categorized into four main types according to the seasons when they are grown and a variety of shapes lengths, colors, and sizes, such as red, pink, white, gray-black, or yellow radishes, with round or elongated roots that can grow longer than a parsnip.
It is not widely known that Beatrix Potter's famous character "Peter Rabbit" is shown eating long scarlet radishes, not carrots, in Mr McGregor's garden.
Sometimes referred to as European radishes or spring radishes if they are planted in cooler weather, summer radishes are generally small and have a relatively short three- to four-week cultivation time.
'Black Spanish' or 'Black Spanish Round' occur in both round and elongated forms, and are sometimes simply called the black radish (Raphanus sativus L. var. niger (M.) S.K. or L. ssp. niger (M.). D.C. var. albus D.C) or known by the French name Gros Noir d'Hiver. It dates in Europe to 1548, and was a common garden variety in England and France during the early 19th century. It has a rough, black skin with hot-flavored, white flesh, is round or irregularly pear shaped, and grows to around 10 cm (4 in) in diameter.
Daikon refers to a wide variety of winter oilseed radishes from Asia. While the Japanese name daikon has been adopted in English, it is also sometimes called the Japanese radish, Chinese radish, Oriental radish or mooli (in India and South Asia). Daikon commonly have elongated white roots, although many varieties of daikon exist. One well-known variety is 'April Cross', with smooth white roots.The New York Times describes 'Masato Red' and 'Masato Green' varieties as extremely long, well-suited for fall planting and winter storage. The Sakurajima radish is a hot-flavored variety which is typically grown to around 10 kg (22 lb), but which can grow to 30 kg (66 lb) when left in the ground.
The seeds of radishes grow in siliques (widely referred to as "pods"), following flowering that happens when left to grow past their normal harvesting period. The seeds are edible, and are sometimes used as a crunchy, spicy addition to salads. Some varieties are grown specifically for their seeds or seed pods, rather than their roots. The rat-tailed radish, an old European variety thought to have come from East Asia centuries ago, has long, thin, curly pods which can exceed 20 cm (8 in) in length. In the 17th century, the pods were often pickled and served with meat. The 'München Bier' variety supplies spicy seed pods that are sometimes served raw as an accompaniment to beer in Germany.
In a 100 gram serving, raw radishes provide 16 calories and have a moderate amount of vitamin C (18% of Daily Value), with other essential nutrients in low content (table).
The most commonly eaten portion is the napiform taproot, although the entire plant is edible and the tops can be used as a leaf vegetable. The seed can also be sprouted and eaten raw in a similar way to a mung bean.
The bulb of the radish is usually eaten raw, although tougher specimens can be steamed. The raw flesh has a crisp texture and a pungent, peppery flavor, caused by glucosinolates and the enzyme myrosinase, which combine when chewed to form allyl isothiocyanates, also present in mustard, horseradish, and wasabi.
Radishes are mostly used in salads, but also appear in many European dishes. Radish leaves are sometimes used in recipes, like potato soup or as a sauteed side dish. They are also found blended with fruit juices in some recipes.
The seeds of R. sativus can be pressed to extract radish seed oil. Wild radish seeds contain up to 48% oil, and while not suitable for human consumption, this oil is a potential source of biofuel. The daikon grows well in cool climates and, apart from its industrial use, can be used as a cover crop, grown to increase soil fertility, to scavenge nutrients, suppress weeds, help alleviate soil compaction, and prevent winter erosion of the soil.
The daikon varieties of radish are important parts of East, Southeast, and South Asian cuisine. In Japan and Korea, radish dolls are sometimes made as children's toys. Daikon is also one of the plants that make up the Japanese Festival of Seven Herbs (Nanakusa no sekku) on the seventh day after the new year.
Citizens of Oaxaca, Mexico, celebrate the Night of the Radishes (Noche de los rábanos) on December 23 as a part of Christmas celebrations. This folk art competition uses a large type of radish up to 50 centimetres (20 in) long and weighing up to 3 kilograms (6.6 lb). Great skill and ingenuity are used to carve these into religious and popular figures, buildings, and other objects, and they are displayed in the town square.
About seven million tons of radishes are produced yearly, representing roughly 2% of the global vegetable production.