Daikon can be grown as a winter cover crop and green manure. These varieties are often named "tillage radish" because it makes a huge, penetrating root which effectively performs deep cultivation.
They bring nutrients lower in the soil profile up into the higher reaches; are good nutrient scavengers, so they are good partners with legumes instead of grasses; if harsh winters, the root will decompose while in the soil in Spring releasing early nitrogen stores.
The growing plant repels beetles from tomatoes and cucumbers. It is also useful for repelling various other insect pests such as carrot root fly.
Very easily cultivated fast-growing plants which prefer a rich light soil with ample moisture. They dislike very heavy or acid soils. Plants are susceptible to drought and require irrigation during dry spells in the summer or the root quality will rapidly deteriorate and the plant will go to seed.
Radishes are a good companion plant for lettuces, nasturtiums, peas and chervil, tomatoes and cucumbers. They are said to repel cucumber beetles if planted near cucumber plants and they also repel the vine borers which attack squashes, marrows and courgettes. They grow badly with hyssop and with grape vines.
Raphanus sativa is most famously grown for it's large edible root but the seeds, flowers and young leaves and seedpods are also often eaten or added to dishes to impart some spice.
The Japanese radishes have higher concentrations of glucosinolate, a substance that acts against the thyroid gland. It is probably best to remove the skin.
Young flower clusters are edible raw or cooked. With a spicy flavour with a crisp pleasant texture, they are reported to make a nice addition to salads or can be used as a broccoli substitute.
Young leaves are edible raw or cooked. A somewhat hot taste, and the texture is somewhat coarse. As long as they are young, they make an acceptable addition in small quantities to chopped salads and are a reasonable cooked green.
Root - raw or cooked. Crisp and juicy, they have a hot and spicy flavour and are a very popular addition to salads. The summer crops do not store well and should be used as soon as possible after harvesting. The winter varieties (including the Japanese forms) have much larger roots and often a milder flavour. These store well and can be either harvested in early winter for storage or be harvested as required through the winter.