Origin
Radishes are found growing wild in Turkey, Palestine and Armenia. The white Radish is common and a staple food in Asia. Spain grows the black variety.
Uses
Radishes are more than decorative garnishes. The tops are eaten as a green vegetable as well as the immature, barely developed roots that result when plants are thinned out. They are good forage for pigs that will root for tubers that have grown too large, are woody, tough and strong flavored.
Cultivation
Radishes are easily grown under conditions that include sun, adequate moisture and soil that is fertilized before planting or is rich with organic matter. Plant seeds close together in loose, light, well-drained soil with hay mulch. They may be planted at the beginning of the cool season and at the very end of the hot season when most of the growth will take place in cooler weather. Radishes must be thinned to allow for root growth. Early varieties should have a 1-in space between and late varieties 2-in to 4-in as they will develop larger roots. Early Radishes must mature quickly (30-45) days before soil temperature rises.
Harvesting and Seed Production
Early Radishes can be pulled up as soon as the root can be seen at ground level and is at least 1-in in diameter. The Japanese daikon (meaning “great root”) can grow to 18 inches in length and 5-6 lbs. in cool weather. For seed production, cut when pods are brown, hang to dry or spread on screens. Pods must be crushed to obtain the few seeds in each. Get rid of chaff and dust and dry seeds for a week. Seeds will last 4 years if stored in airtight containers.
Pests and Diseases
Root maggots are the most common pests especially above 40 degrees north latitude.
Cooking and Nutrition
Early and late maturing Radishes can be eaten raw but larger ones are also cooked, preserved by pickling, or added to soups and stews. In Japanese cooking, peeled, grated daikon is always added to tempura dipping sauce. It is thought to aid in digestion especially of fatty foods. Daikon greens are finely cut, salted, stored for a week and added to rice or other recipes. The foliage can also be cooked like spinach in large amounts of water to eliminate bitterness. Radishes are low in calories and good sources of potassium, vitamin C, folate and fiber. It is best to remove the green tops before storing fresh radishes in the refrigerator. Later varieties can remain in the ground until the ground freezes, then stored for several months if kept in a moist, very cool environment.
References
http://ecocrop.fao.org/ecocrop/srv/en/cropView?id=1839
http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=278044&isprofile=0&letter=R