Radishes are a cool weather crop that will tolerate some heat. Sow radishes in the garden as soon as the soil can be worked in spring and plant succession crops every 10 days until the end of spring.
Lifting radishes as soon as they are large enough to eat is important. Radishes that stay too long in the garden will become woody. Radishes germinate readily and grow rapidly so don't sow radishes too thickly and thin seedlings right away so that they don't stand closer than 1½ inches apart.
For radish growing tips see How to Grow Radish or Radish Growing Success Tips at the bottom of this post.
Here are common radish growing problems with cures and controls:
Roots fail to form.Seed are sown too thickly. Thin radishes early and harvest roots as soon as they are large enough to eat. Thin seedlings to 1½ to 2 inches apart.
Seeds rot or seedlings collapse with dark water-soaked stems as soon as they appear.Damping off is a fungus that lives in the soil, particularly where humidity is high. Do not plant in cold, moist soil. Make sure soil is well drained.
Tiny shot-holes in leaves of seedlings.Flea beetles are tiny bronze or black beetles a sixteenth of an inch long. They eat small holes in the leaves of seedlings and small transplants. The larvae feed on roots of germinating plants. Spread diatomaceous earth around seedling. Cultivate often to disrupt life cycle. Keep garden clean.