Kohlrabi is a member of the Brassica family, related to cabbage and broccoli. The edible part is the swollen, above-ground stem, which forms a globe-like “bulb” just above the soil line. Raw kohlrabi is crisp, juicy, and offers a refreshing, mildly sweet flavor, often compared to a blend of mild turnip and broccoli stem. This versatile ingredient is perfect for slaws and salads.
Timing and Location Requirements
Kohlrabi is a cool-season crop that thrives in moderate temperatures, ideally between 60°F and 75°F. Planting must be timed so the plant matures before hot weather arrives, as temperatures exceeding 75°F cause the stem to become tough and bitter. For a spring harvest, set plants out four weeks before the last expected frost. For an autumn crop, sow seeds six to eight weeks before the first expected fall frost.
Kohlrabi requires a location that receives ample sunlight, ideally a minimum of six hours of direct sun daily. Consistent moisture and cool temperatures promote the rapid growth necessary for tender, sweet bulbs. While kohlrabi tolerates various soil types, it performs best in fertile, well-draining loamy soil rich in organic matter.
Starting Kohlrabi: Seeds or Transplants
Gardeners can establish kohlrabi by direct sowing seeds or planting transplants. Direct sowing is often preferred because it avoids transplant shock, which can stunt growth and affect bulb quality. Seeds can be sown directly into the prepared garden bed as soon as the soil is workable in early spring.
To achieve an earlier harvest, start seeds indoors four to six weeks before the target transplant date. Seedlings are ready to move outside when they have developed four to six true leaves and a healthy root system.
Before planting indoor-started seedlings, they must be gradually acclimated to outdoor conditions through hardening off. This involves exposing the young plants to increasing periods of wind and direct sunlight over seven to ten days. This transition minimizes stress and prevents bolting, where the plant prematurely focuses energy on flowering instead of bulb development.
Preparing the Planting Site and Spacing
Preparing the soil before planting ensures kohlrabi has the best chance for fast, continuous growth. Loosen the planting area to a depth of at least 12 inches to encourage healthy root development. Incorporating two to three inches of well-aged compost or rich organic matter significantly improves soil fertility and drainage.
Kohlrabi thrives in soil with a neutral to slightly acidic pH, ideally ranging from 6.0 to 7.5. Sow seeds shallowly, about one-quarter to one-half inch deep. When planting transplants, place seedlings at the same depth they were growing in their pots, taking care not to bury the crown or the developing bulb.
Proper spacing is necessary for correct bulb swelling and air circulation, which prevents disease. Allow six to eight inches between individual plants within the row. Rows should be spaced 12 to 18 inches apart to provide room for working and for the leaves to expand fully.
Initial Care for Successful Growth
Immediately after planting, thoroughly water the soil to settle it around the roots and reduce transplant stress. Consistent, even moisture is necessary for kohlrabi development, as water fluctuations cause the stem to become tough and woody. Plants require approximately one to 1.5 inches of water per week, delivered through rainfall or supplemental irrigation.
For direct-sown rows, thinning the seedlings is mandatory once plants display their first two sets of true leaves. Remove weaker seedlings to achieve the final spacing of six to eight inches between plants. This eliminates competition for nutrients and light, allowing remaining plants to form large, tender stems.
Apply a light layer of organic mulch, such as straw or shredded leaves, around the young plants. Mulch conserves soil moisture and keeps the soil temperature cooler, which benefits this cool-season crop. It also suppresses weed growth that would compete with the shallow kohlrabi roots.