Kohlrabi is a hardy biennial grown as an annual. Sow kohlrabi seed in the garden 3 to 4 weeks before the last average frost date in spring. Kohlrabi grows best in cool temperatures between 40°F and 75°F (4.4°C and 23.9°C). Kohlrabi requires 45 to 60 days to reach maturity. In warm winter regions, sow kohlrabi in late summer for winter harvest. Kohlrabi can withstand an early autumn frost.
Description. Kohlrabi is a hardy biennial grown as an annual. Kohlrabi has a swollen globe-shaped stem that makes it look like a turnip growing on a cabbage root. Stems can be white, purple, or green and is topped with a rosette of long-stemmed blue-green leaves. Kohlrabi is milder and sweeter than either cabbage or turnip.
Yield. Plant 4 to 5 kohlrabi per household member.
Site. Plant kohlrabi in full sun. Grow kohlrabi well-worked, well-drained soil rich in organic matter. Kohlrabi prefers soil within the 5.5 to 6.8 range. Work aged compost into planting beds before sowing. Side dress kohlrabi with aged compost at midseason.
Planting time. Kohlrabi is a cool-weather crop. Sow kohlrabi seed in the garden 3 to 4 weeks before the last average frost date in spring. Kohlrabi requires 45 to 60 days to reach maturity and should be grown so that it comes to harvest before temperatures average greater than 75°F (23.9°C). In warm winter regions, sow kohlrabi in late summer for winter harvest. Kohlrabi can withstand an early autumn frost. In cold winter regions, sow kohlrabi in summer for early autumn harvest.
More tips at Kohlrabi Seed Starting Tips.
Planting and spacing. Sow kohlrabi seed ½ inch deep and 1 inch (2.5 cm) apart; thin successful seedlings from 5 to 8 inches apart. Space rows 18 to 24 inches (45-60 cm) apart. Thinned seedlings can be transplanted to another part of the garden.
Companion plants. Beets, celery, herbs, onions, potatoes. Do not plant with pole beans, strawberries or tomatoes.
Container. Kohlrabi is large rooted and not well suited for container growing.
Caring for Kohlrabi
Water and feeding. Keep soil evenly moist for quick growth. Kohlrabi that goes without water will become woody. Prepare planting beds with aged compost. Side dress kohlrabi with aged compost at midseason.
Care. Cultivate carefully to avoid harming the shallow roots. Mulch kohlrabi with aged compost when plants are 4 to 5 inches (10-12 cm) tall.
Pests. Kohlrabi can be attacked by cutworms, cabbage loopers, and imported cabbage worms. Place collars around stems to protect seedlings from cutworm damage. Remove egg clusters from underneath leaves and wash plants with diluted soap solution. Cabbage worms can be controlled by spraying with Bacillus thuringiensis.
Diseases. Kohlrabi is susceptible to cabbage yellows, clubroot, and downy mildew. Plant disease-resistant varieties. Remove and destroy infected plants.
Harvesting and Storing Kohlrabi
Harvest. Kohlrabi is ready for harvest when stems reach 2 to 3 inches in diameter.
More tips at How to Harvest and Store Kohlrabi.
Storing and preserving. Kohlrabi will store well in the refrigerator for 1 week or for one to two months in a cold, moist place. Kohlrabi can be frozen.
Kohlrabi Varieties to Grow
Varieties. ‘Early Purple Vienna' (60 days); ‘Early White Vienna' (55 days); ‘Grand Duke' (50 days); ‘Purple Danube' (52 days);
Common name. Kohlrabi, turnip-rooted cabbage, stem turnip, turnip cabbage
Botanical name. Brassica oleracea, Gongylodes group