The German Giant is my favorite Radish. It's not fancy or hard to grow and tastes great at any size. The Radish may be a cool-weather crop but I continue to have success even in South Florida.
Grow radishes in full sun or partial shade. Plant radishes in loose, well-drained soil. Remove soil lumps, rocks, and roots from radish planting beds. Obstructions can cause roots to grow malformed. Add organic matter to planting beds before sowing radishes. Radishes prefer a soil pH of 5.5 to 6.8.
Sow radish seed ½ inch deep and 1 inch apart; thin successful seedlings from 1 to 4 inches apart in wide rows depending upon the variety.
Sow radishes in the garden 2 to 3 weeks before average date of the last frost in spring. Sow succession crops every 2 weeks in spring and in autumn. Two or more crops can be grown in spring. Radishes require 22 to 70 days to come to harvest. Warm weather can result in small roots. Long days may also cause radishes to flower; plant radishes during the shorter days of spring and autumn. In mild winter regions, grow radishes in late autumn and early winter. Radishes can withstand frost.
Keep radish planting beds moist but not wet. Even, regular watering will result in quick growth. Radishes that receive too little water will become woody tasting. Prepare planting beds with aged compost. Side dress radishes with aged compost at midseason.
Radishes can be grown in containers. Sow radishes in containers at least 6 inches deep. Plant radishes in round containers in concentric circles. Move containers to cool locations if the weather grows warm.