Radish Seed Starting Tips

Radish seedlings

Radish is a cool-season crop. Radishes are best grown in spring and fall.

Direct sow radishes in the garden 6 to 3 weeks before the last frost in spring. Sow succession crops every 3 weeks after.

Growing tip: Shorter and cooler days result in radishes with rounder roots. For mild and tender roots, grow radishes rapidly with plenty of moisture in soil rich in aged compost. When growth is interrupted by lack of soil moisture, radish roots will be hot, tough, and pithy.

Radishes mature in 21 to 35 days depending on the variety.

Sowing and Planting Tips:

  • Start radishes from seed sown directly in the garden.
  • Seed is viable for 5 years.
  • Start seeds in the garden about 6 to 4 weeks before you expect the last frost in spring. Radish can be started indoors, but they—like most root crops—are difficult to transplant to the garden with success.
  • If started indoors and transplanted, allow two additional weeks to maturity as a result of root insult at transplanting; nip off the long thread tip of the radish root when transplanting.
  • Sow seed ¼ to ½ (6-12 mm) inch deep and be sure to heel or stamp the soil firmly.
  • Sow seed 1 inch (2.5 cm) apart and later thin to 4 inches (10 cm) in all directions.
  • To improve germination sow seed at dusk or on a cool, cloudy day.
  • Sow seed in loose, fertile soil. Adding aged compost to planting beds in advance of sowing will feed the soil and aide moisture retention.
  • Seeds should germinate in 4 to 10 days at an optimal temperature of 70°F (21C) or greater; germination will take longer in colder soil.
  • Optimum soil temperature to grow radishes is 50° to 75°F (10-24°C).
  • Make additional sowing at 3-week intervals for a continuous harvest; but time sowing so that crop does not mature in hot weather.
  • Radishes prefer a soil pH range of 5.5 to 6.5.
  • Grow radishes in full sun for best yield—tolerates partial shade.
  • Fertilize with an organic fertilizer such as fish emulsion at half strength.
  • Common pest enemies are aphids, flea beetles, and cabbage root maggots, cabbage worms, cabbage loopers, and wire worms. Protect the seedlings from pests and cold for two to three weeks after planting with spun poly row covers.

Interplanting: Plant radish with bush beans, beets, carrots, cucumbers, lettuce, peas, peppers, and spinach.

Container Growing: Grow in a container at least 4 inches (10 cm) deep; plant in concentric circles.

Recommended Planting Calendar:

  • 8-6 weeks before the last frost in spring: direct-sow in a plastic tunnel or cold frame.
  • 6-3 weeks before the last frost in spring: direct-sow in the garden.
  • Every 2 to 3 weeks sow succession crops.

For Fall Harvest:

  • 10-8 weeks before the first frost in fall: direct-sow in the garden.
  • 4-2 weeks before the first frost in fall: direct-sow in the garden, in a plastic tunnel, or cold frame.

Recommended Varieties: ‘Cherry Belle’ is classic round, and red; ‘Easter Egg’ is multicolored; ‘French Breakfast’ is long and cylindrical; ‘Miyashige’ is an Asian daikon radish with long white roots.

Botanical Name: Raphanus sativus

Radish belongs to the Brassicacea (Cruciferae) or cabbage family; other members include cabbage, kale, collard, broccoli, Brussels sprouts, and turnips.