Kohlrabi Seed Starting Tips

Kohlrabi seedling

Kohlrabi is a cool-season crop; it’s best grown in spring and fall.

Kohlrabi is not a root crop; the edible part of the plant is a swollen portion of the stem growing above the soil.

Kohlrabi can be eaten raw or cooked, and it stores well for winter use.

To be tender and tasty, kohlrabi must be grown quickly and without interruption. It’s important to keep the soil just moist and grow kohlrabi in soil rich in organic matter and aged compost.

Sow kohlrabi in spring for early summer harvest and use; start a second crop in mid- to late summer for winter storage and use.

Kohlrabi matures in 45 to 60 days depending on the variety.

Sowing and Planting Tips:

  • Start kohlrabi from seed sown indoors or directly in the garden.
  • Seed is viable for 4 years.
  • Start seeds in the garden about 8 to 4 weeks before you expect the last frost.
  • 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 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 2 inches (5 cm) apart and later thin to 5 to 8 inches (13-20 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 5 to 10 days at an optimal temperature of 70°F (21C) or thereabouts; germination will take longer in colder soil.
  • Optimum soil temperature to grow kohlrabi is 65°F (18°C).
  • Make additional sowing at 3-week intervals for a continuous harvest; but time sowing so that crop does not mature in hot weather.
  • Kohlrabi prefers a soil pH range of 5.5 to 6.8.
  • Grow kohlrabi in full sun for best yield—tolerates partial shade.
  • Fertilize with an organic fertilizer such as fish emulsion at half strength.
  • Common pest enemies include aphids, flea beetles, and cabbage root maggots, cabbage worms, and cabbage loopers.
  • Protect the seedlings from pests and cold for two to three weeks after planting with spun poly row covers.

Interplanting: Plant kohlrabi with bush beans, beets, celery, cucumbers, lettuce, and onions.

Container Growing: Choose a container 6 inches across or more for each plant and 8 inches deep.

Recommended Planting Calendar:

  • 10-8 weeks before the last frost in spring: start seed indoors.
  • 8-6 weeks before the last frost in spring: direct sow seed in a plastic tunnel or cold frame.
  • 4-3 weeks before the last frost in spring: direct-sow seed in the garden.
  • 3-2 weeks before the last frost in spring: transplant seedlings to the garden.

For Fall and Winter Harvest:

  • 14-12 weeks before the first frost in fall: start seed indoors.
  • 12-10 weeks before the first frost in fall: direct-sow seed in the garden for fall harvest.
  • 10-8 weeks before the first frost in fall: direct-sow seed in a plastic tunnel or cold frame.
  • 8-6 weeks before the first frost in fall: transplant seedlings to the garden.

Recommended Varieties: ‘Rapid’ matures early; ‘Grand Duke’ is a midseason hybrid; ‘Purple Danube’ and ‘Purple Vienna’ are favorites.

Botanical Name: Brassica oleracea var. gongylodes

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