Radishes prefer cool weather. Direct sow seeds outdoors 3/24 – 6/15. For fall, sow seeds 8/21- 9/7. Plant seeds ½” deep, 1” apart in rows spaced 8” apart. Days to germination: 3 - 6 (longer in cool soil). Keep seeds and plants consistently moist. Space saving tip: Try interplanting radish seeds with beet seeds. The early radish will mature long before the beet. Use crop rotation to avoid clubroot (all brassicas). If necessary, cover with row cover fabric to protect against flea beetles and cabbage root maggots.
Harvest radishes as soon as they reach full size. Do not leave them in the ground too long or they will become pithy.
Radishes require vernalization (exposure to cold weather) in order to bolt, flower, and produce seed. Sow “Spring” radish seeds no later than 3/24 - 4/15 so that plants will be exposed to cold spring weather. Radishes are insect pollinated and are cross pollinated – they will cross with all other radishes that are blooming nearby. Isolation distance: ½ mile. Minimum population size: 10-50. Dig radishes and identify best roots for replanting for seed (clip off leaves before replanting). Space 2 - 3 feet apart. Stake plants. Clip seed pods when seeds are fully ripe. Dry process.