Radishes prefer cool weather. Direct sow seeds outdoors March 24th – June 15th. For fall, sow seeds Aug. 21st - Sept. 7th. 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 are ready or else they will turn pithy if left in the ground too long.
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.