Radishes are of several types. Some of them are annuals, others are biennials and they are all grown for the swollen roots. The small types can be either round and measure up to 2.5 cm in diameter, either long and grow up to 7 cm long. Large forms include oriental radishes known as mooli or daikon and the large, overwintering, winter radishes. The round large form may grow over 23 cm in diameter and the long form will grow up to 60 cm long.
Radish skin color can be white, pink, red, yellow, purple, black or green, and the flesh of all species is normally white. Small roots are eaten raw when fresh and large roots are used raw or cooked, fresh or stored. Immature seed pods from some cultivars and young seedling leaves from most cultivars are edible raw.
Radishes are mainly a cool-season crop, but now you can find cultivars that can be grown in a wide range of growing conditions. All overwintering species and some mooli types are frost-tolerant. Grow them in an open site, in light, rich, well-drained soil. Never allow them to dry out and if the weather is dry, water the crop every week at a rate of 11 liters per square meter. Make sure you do not overwater them as this will encourage leaf production rather than root development. Make sure you rotate the radish crop as they may be attacked by flea beetles, cabbage root fly and slugs.
Saw small types outdoors throughout the growing season, starting when the soil is workable. For a continuous crop, sow radishes at 15 days intervals. They are ready to harvest 3-4 weeks after sowing. For extending the growing season, very early and late sowings may be made undercover. Sow overwintering radishes in summer. For small types, broadcast seeds very thinly or sow 1 cm deep in drills 15 cm apart. Thin the seedlings to at least 2.5 cm apart, never letting them to become overcrowded. If possible sow seeds 2.5 cm apart so that no thinning is needed. Large types of radishes may be sown 2 cm deep in rows of about 23 cm apart, thinning them to 15-23 cm apart, depending on the cultivar.
Small radishes type mature 3-4 weeks after sowing and large one after 8-10 weeks. Harvest small types as they mature since they will become woody if left in the ground for long. Large types may be left in the ground for several weeks with no risk of deterioration. Overwintering types may be left in the soil for lifting when required, except in severe winter weather or in heavy soils. In these cases, lift and store them in boxes of moist sand in a frost-free place or outside in clamps for three or four months.
Propagation is done by seeds. To collect your own seeds, leave a few plants to produce seeds. Harvest the pods while they are still young and green. Dry them and collect the seeds.