Date: Aug 2007 Author: Doug Hocking
Radish (Raphanus sativus) belongs to the Cruciferae (Brassicaceae) or mustard family. The botanical name Raphanus is a Latin form of the Greek for radish. It is said to derive from a phrase meaning ‘easily reared’. This is appropriate considering the plant’s wide adaptability and its short period from sowing to maturity. The radish has been cultivated for a long time. Writings of ancient naturalists show that it was popular in Egypt at the time of the pharaohs.
In New South Wales, commercial radish production is mainly confined to the Sydney and outer metropolitan district. Radishes are generally marketed fresh in the central wholesale markets.
The radish is essentially a cool-season crop. It grows best in the spring and autumn and will tolerate light winter frosts. The high temperatures of summer cause the plant to develop small tops, and roots rapidly become pithy and strongly pungent after reaching maturity. For this reason producing quality radishes during midsummer can be difficult.
Radishes do best on the lighter, sandy, well-drained soils. This allows for even root development and ease of washing after harvest.
There are several types of radish that can be grown. The main differences between them are in size, shape and colour of the root. The main types grown are globe, oval, oblong and long.
These varieties are generally quite spherical in shape and are mostly red in colour. Varieties include Red Prince, Scarlet Knight and Fireball.
These varieties are not a true globe shape but are slightly oval. The main varieties in this group are Mars and Mars Improved. The Mars types of radish are the major varieties grown in New South Wales.
This type is nearly cylindrical with a blunt, rounded tip. They are either plain red or plain white or red and white. Some varieties are Red Baron (red), French Breakfast (red with white tip; 5 cm long), Inca (red, 5 cm long) and White Icicle (white, 10 cm long).
This type has long tapered roots. Cultivars are either red or white. Long White and Hybrid Long White are the more popular with commercial growers. Roots are 35 to 40 cm in length.
There are several types grown depending on the requirements of the ethnic group. Chinese and Indo-Chinese require a white-necked thin root (5 cm diameter) growing to 25 cm in length. The Japanese prefer the green-necked fat root (7–10 cm diameter) grown to 30–35 cm in length.
A fine, well-prepared seed bed is important for growing radishes. The application of animal manure or compost approximately 6 weeks before sowing helps build up the water-holding capacity of the soil and balance the nutrient supply.
Liberal applications of animal manure are normally used for growing radishes. Apply a good quality fowl manure at the rate of 15 t/ha (1.5 kg/m2) two to three weeks before planting. Prior to sowing, broadcast 100 g/m2 of 5:5:5 N:P:K fertiliser. This ensures that the young seedlings have a ready supply of major elements immediately after germination. This is important for radishes, as they have such a short growing period.
Radishes will tolerate slightly acid soil, but the pH should not be allowed to fall below 5.5. To avoid using excessive fertiliser, apply fertiliser according to a soil analysis.
Seed is sown 10–20 mm deep in rows about 20 cm apart. Plants germinate 4–8 days after sowing. A density of 40–55 plants per metre of row is desirable and early thinning may be required to achieve this. Excessive plant densities will produce irregular-sized, misshapen roots.
To produce a high quality radish, plants must make continuous growth. One way to ensure this is to maintain satisfactory soil moisture throughout the growth of the plant. This will often mean irrigating every day in the warmer months of the year.
Because radishes have such a short growing period and are grown only in small areas, weed control is generally not a serious problem. If weeds are a problem, encourage the weed seeds to germinate and control them with a knockdown herbicide prior to planting radishes. It may also be necessary to use inter-row cultivation and hand-weeding during the growth of the crop.
As a member of the crucifer family, radishes are attacked by the same pests which attack cabbages and cauliflowers. Major pests include cabbage white butterfly, aphids and diamondback moth. Other pests of crucifers will cause damage from time to time.
Because of the short growing period, only a few diseases cause economic losses in radishes. The most important is black rot, a disease caused by a soil-borne fungus. Dark irregular patches develop on the radish root and eventually give the entire root a black colour. Long-rooted cultivars can be severely attacked. The round types may escape infection in infested soil but are not resistant. The disease is controlled by good soil drainage and crop rotations of 3–4 years.
Radishes are also attacked by white rust. This disease causes raised white pustules on the leaves, stems and flowers. It is controlled by the destruction of diseased crop residues, rotations of 3–4 years and the separation of young from old crops.
Under normal conditions, harvest commences 6 weeks after planting. Roots are mature when they reach a satisfactory size. Radishes are harvested by hand and either tied in bunches of a dozen roots or sold in bulk to prepackers who top them and then sell them by weight in prepacks. Daikon radish can be processed and an emerging market is developing for the dried and pickled product.
Radishes are very susceptible to wilting. Harvest them in the cool and keep them cool and moist until they can be put into cool storage at a temperature of 0°C and a relative humidity of 90%.