Kohlrabi is among the many "cole crops" grown in the home vegetable garden. Cole crops is a general term used to describe several vegetables in the mustard family, including broccoli, Brussels sprouts, cabbage, cauliflower, collards, kale, and kohlrabi. All cole crops are cultivated varieties of the species Brassica oleracea. Cole crops are cool-season vegetables that grow best at temperatures between 60° and 70°F and can withstand light frosts without injury.
Suggested Cultivars | Planting | Care | Potential Problems | Harvest & Storage | More Information
Suggested Cultivars for Iowa
- Early Purple Vienna – early; reddish purple with white flesh
- Kolibri – deep purple with white flesh
- Quickstar – pale green with white flesh
- Winner – pale green with white flesh
Planting
Kohlrabi is best direct sown in the garden in early spring. A second crop can be sown in mid-to-late summer for fall harvest. While direct sowing into the garden is preferred, plants can be started indoors 4 to 5 weeks before transplanting outdoors.
Schedule
Direct sown kohlrabi seed in the garden in early to mid-April in central Iowa. (Gardeners in southern Iowa can plant about one week earlier, while those in northern counties should wait one week later.) Depending on the cultivar, plants are ready to harvest 50-60 days after sowing. This is typically early to late June.
For a fall crop, direct sow seed in the garden anytime between mid-July and mid-August. Harvest can be expected from mid-September to early October, depending on when the seed was sown.
Site
Cole crops, like kohlrabi, perform best in fertile, moist, well-drained soils. An ideal soil pH is between 6 and 7. The planting site should also receive at least 6 hours of direct sun each day. To avoid disease problems, rotate the placement of cole crops in the garden. If possible, plant cole crops in a given area only once every 3 or 4 years.
Spacing
When planting kohlrabi in the garden, sow seeds in rows spaced 18 to 24 inches apart. Thin seedlings when they form their first or second set of true leaves. After thinning, kohlrabi seedlings should be spaced 6-8 inches apart within the row.
Care
Watering
Most cole crops, such as kohlrabi, have shallow root systems and require weekly irrigation if rainfall doesn’t provide one inch of water per week. If possible use soaker hoses or drip irrigation systems to prevent wetting the foliage. Watering only the plant's root zone can also reduce the number of weeds that may germinate. Learn more about watering in this article: Watering Tips for the Garden, Lawn, and Landscape.
Fertilizing
If a soil test has not been done, apply 1-2 pounds of all-purpose garden fertilizer, such as 10-10-10, per 100 square feet, and incorporate it into the top 4-6 inches of soil before planting. Conduct a soil test to get more precise fertilizer recommendations based on your garden's fertility.
About 3-4 weeks after planting, broadcast a small amount of an all-purpose garden fertilizer in a band along one side of each row.
Mulching & Weeding
Control weeds to prevent competition for water, nutrients, and light. Shallow cultivation, hand pulling, and mulching are the best weed control options.
A 2-3 inch layer of mulch, such as straw, dry grass clippings, or shredded leaves, helps control weeds and conserves soil moisture. Learn more about weed control in this vegetable garden in this article: Weed Control in the Vegetable Garden.
Potential Problems
Cabbageworms
Cabbageworms are greenish caterpillars that eat large, irregular holes in the foliage of most cole crops. Treat when caterpillars are first noticed with products containing Bacillus thuringiensis (Bt). When consumed by cabbageworms, this bacterium produces toxins which destroy the insects. Synthetic and other organic pesticides also can be used.
Flea Beetles
Flea beetles eat small, round holes in the foliage, resulting in “shothole” damage. Adults are tiny, shiny, black beetles. They possess large hind legs that enable them to jump.
Minor flea beetle damage will have little effect on crop yields. If significant damage begins to appear, treat plants with an insecticide. As always, carefully read and follow label directions when using pesticides.
Harvest & Storage
Kohlrabi is typically ready to harvest 50-60 days after sowing seed in the garden, depending on the cultivar.
Harvest kohlrabi when the thickened stems are 2 to 3 inches in diameter. (Kohlrabi larger than 3 inches in diameter will be tough, woody, and bitter.) Simply pull the entire plant from the ground and remove the leaves and roots.
Store in perforated plastic bags in the refrigerator for up to 3 weeks.
With good management practices, the average yield per 10-foot row of kohlrabi is 7-8 pounds. Each plant produces one kohlrabi.
More Information
- Cole Crops (publication)
- Growing Broccoli in the Home Garden
- Growing Cauliflower in the Home Garden
- Growing Cabbage in the Home Garden
- Growing Brussels Sprouts in the Home Garden
- Vegetable Harvest Guide
- Vegetable Planting and Harvesting Times
- Planting and Harvesting Times for Garden Vegetables (publication)
- Fall Planting of Vegetables
- Crop Rotation in the Vegetable Garden
- Weed Control in the Vegetable Garden