Best grown in full sun in loamy or sandy soils. Can be seeded directly in two-week intervals between mid-April and the first of May for a spring crop and in the month of August for a fall crop. Radishes become tough and develop a hotter taste as they become older. Harvest when young before radishes bolt and become woody.
Daikon radishes (R .s. Longipinnatus Group) are best planted in July and August when soil temperatures are above 60 degrees F and the radishes have an opportunity to mature by fall. Sow seeds in full sun directly into the garden 1/4 to 1/2" deep, firming the soil somewhat after planting. Thin to 4 or 6" apart to ensure adequate room for root development. Before sowing, be sure the soil is cultivated and loose as deep as the radishes will be long. Raised beds are ideal for long radishes. Keep well fertilized and watered to insure mild flavor and tenderness.
Radishes have had a long relationship with man. Southern Asia is believed to be the country of origin since truly wild forms have been found there. Middle Asia and India appear to be secondary centers where many different forms developed subsequently. Third-century B.C. Greeks wrote of their radishes, and by 100 A.D., Roman writers described small and large types, mild and biting varieties, and round and long forms. A German botanist in 1544 reported radishes of 100 pounds. Radishes appear to be one of the first European crops introduced into the Americas, closely behind the arrival of Columbus.
The white daikon (“big root” in Japanese) is common in Japan, and gardeners in increasing numbers are growing it here. The daikon has a milder, sweeter flavor than ordinary radishes. The root shape of all varieties is either long and cylindrical or short and round. The cylindrical roots range from 6" to 2' long and are either tapered or blunt at the end. The round varieties are the size of a baseball.
Flea beetles can be a problem as well as other pests typically found on Brassicaceae crops. Floating row covers can be very useful.