How To Grow Kohlrabi: The Complete Care Guide

Introduction

Kohlrabi, often called the “German turnip” or “cabbage turnip,” is one of the most underappreciated vegetables in the home garden. This unique member of the Brassica family produces a distinctive swollen stem that grows above ground, resembling a small alien spacecraft crowned with leafy greens. Despite its unusual appearance, kohlrabi offers exceptional culinary versatility and nutritional value that rivals its more popular cousins like broccoli and cabbage.

Native to northern Europe, kohlrabi has been cultivated for over 400 years and remains a staple in German, Austrian, and Eastern European cuisines. The name itself derives from the German “kohl” (cabbage) and “rabi” (turnip), perfectly describing its flavor profile that combines the mild sweetness of cabbage with the crisp texture of turnip. Rich in vitamin C, fiber, and potassium, kohlrabi provides excellent nutrition while being remarkably easy to grow in cool-season gardens. Its fast growth rate and tolerance for both heat and cold make it an ideal crop for succession planting, providing fresh harvests from spring through fall in most climates.

Growing Conditions & Requirements

Kohlrabi thrives as a cool-season crop that can tolerate a remarkably wide range of growing conditions. Hardy in USDA zones 2-11, it demonstrates exceptional cold tolerance, withstanding temperatures as low as 20°F (-6°C) once established, while also performing reasonably well in warmer conditions when provided adequate moisture and some afternoon shade.

This versatile brassica prefers full sun but tolerates partial shade, especially in warmer climates where 4-6 hours of direct sunlight daily will suffice. In regions with intense summer heat, morning sun with afternoon protection actually improves bulb quality and reduces the likelihood of bolting.

Soil requirements are relatively flexible, though kohlrabi performs best in well-draining, fertile soil with a pH between 6.0-7.5. The plant tolerates slightly alkaline conditions better than most vegetables, making it suitable for gardens with naturally high pH. Rich, loamy soil amended with compost produces the largest, most tender bulbs, but kohlrabi will grow successfully in average garden soil.

Consistent moisture is crucial for proper bulb development. Plants require approximately 1-1.5 inches of water weekly, either from rainfall or irrigation. Inconsistent watering leads to woody, tough bulbs and increases the risk of splitting. Space plants 4-6 inches apart in rows 12-18 inches apart, as overcrowding results in smaller bulbs and increased competition for nutrients.

Planting & Establishment

Timing is critical for successful kohlrabi production. For spring crops, start seeds indoors 4-6 weeks before the last expected frost, or direct seed 2-4 weeks before the last frost date. The optimal soil temperature for germination ranges from 45-85°F, with seeds typically sprouting in 4-7 days under ideal conditions.

Fall crops often produce superior quality bulbs due to cooler growing conditions. Plant fall crops 10-12 weeks before the first expected hard frost, typically in late summer. Many gardeners find fall kohlrabi sweeter and more tender than spring crops. Using a cold frame for vegetables can extend the fall harvest even further into winter in colder climates.

Site selection should prioritize areas with good air circulation to prevent fungal diseases common in brassicas. Avoid planting in locations where other brassica family crops grew the previous season to reduce soil-borne disease risks.

Prepare planting beds by incorporating 2-3 inches of compost or well-aged manure to improve soil structure and fertility. When direct seeding, plant seeds ¼ to ½ inch deep, sowing more densely than final spacing and thinning as seedlings develop. For transplants, harden off seedlings gradually over 7-10 days before transplanting outdoors.

Succession planting every 2-3 weeks extends the harvest season significantly. This practice is particularly valuable since kohlrabi bulbs are best harvested within a narrow window of optimal tenderness.

Propagation Methods

Kohlrabi propagation relies primarily on seed, as this annual crop doesn’t reproduce vegetatively under normal growing conditions. High-quality seed remains viable for 3-4 years when stored properly in cool, dry conditions, though germination rates decline after the first year.

For seed starting indoors, use sterile seed-starting mix in individual cells or small pots to minimize transplant shock. Maintain soil temperature between 60-70°F for optimal germination rates. A humidity dome for seedlings can help maintain consistent moisture and warmth during germination. Seedlings are ready for transplanting when they develop 3-4 true leaves, typically 4-5 weeks after seeding.

Direct seeding often produces stronger plants with better root development, particularly important for kohlrabi since the harvested portion develops from the stem near soil level. When direct seeding, plant 2-3 seeds per intended plant location and thin to the strongest seedling once plants are 2-3 inches tall.

Seed saving requires allowing selected plants to complete their biennial lifecycle. Since kohlrabi is typically harvested in its first year, seed production requires overwintering plants in zones 7 and warmer, or lifting and storing bulbs in colder regions. Cross-pollination with other Brassica oleracea varieties can occur, so isolation or caging may be necessary to maintain variety purity.

Care & Maintenance

Consistent care throughout the growing season ensures optimal bulb development and quality. Maintain even soil moisture through regular watering, applying water at soil level to prevent foliar diseases. Mulching around plants helps retain moisture, suppress weeds, and maintain consistent soil temperature.

Fertilization should begin with soil preparation using compost or balanced organic fertilizer. Side-dress plants with nitrogen-rich fertilizer 3-4 weeks after transplanting or when direct-seeded plants reach 4-5 inches tall. Avoid excessive nitrogen late in the season, as this can delay bulb formation and promote leafy growth at the expense of bulb development.

Regular cultivation helps control weeds and prevents soil compaction, but work carefully around shallow roots. Hand-pulling weeds near plants prevents root damage that can stunt growth or create entry points for diseases.

Monitor plants regularly for signs of stress, disease, or pest issues. Early detection and intervention prevent minor problems from becoming major crop losses. If a sudden cold snap is forecast, take steps to protect plants from frost to maintain bulb quality. Remove any yellowing or damaged leaves promptly to improve air circulation and reduce disease pressure.

Unlike some brassicas, kohlrabi requires no pruning or training, though harvesting outer leaves for cooking doesn’t harm bulb development and can actually improve air circulation around plants.

Nutritional Information

Kohlrabi delivers impressive nutritional value with relatively few calories, making it an excellent choice for health-conscious gardeners. One cup of raw kohlrabi (135 grams) contains approximately 36 calories, 8 grams of carbohydrates, 5 grams of fiber, and 2 grams of protein.

The vitamin C content is particularly noteworthy, with a single cup providing over 80% of the daily recommended value. This makes kohlrabi an excellent immune system supporter, especially valuable during fall and winter months when fresh vitamin C sources become scarce.

Mineral content includes significant amounts of potassium (472mg per cup), which supports heart health and proper muscle function. Kohlrabi also provides meaningful quantities of manganese, copper, and phosphorus, along with smaller amounts of calcium, magnesium, and iron.

Like other brassica vegetables, kohlrabi contains glucosinolates, sulfur-containing compounds that break down into beneficial isothiocyanates during digestion. These compounds have been studied for their potential anti-inflammatory and cancer-protective properties.

The leaves are equally nutritious, containing higher concentrations of vitamins A and K compared to the bulb, along with folate and additional vitamin C. Including both bulb and leaves in meals maximizes the benefits of eating locally grown food from your own garden.

Culinary Information

Kohlrabi’s culinary versatility extends far beyond its reputation as a simple root vegetable substitute. The bulb can be consumed raw or cooked, while the leaves serve as excellent cooking greens similar to collards or kale.

Raw kohlrabi offers a crisp, refreshing texture with a mild, slightly sweet flavor reminiscent of broccoli stems or water chestnuts. Young bulbs are tender enough to eat like apples, while larger specimens benefit from peeling to remove the sometimes fibrous outer layer. Grated or julienned raw kohlrabi adds excellent crunch to slaws, salads, and wraps.

Cooking transforms kohlrabi’s texture while mellowing its flavor. Roasting brings out natural sweetness and creates a tender, almost creamy interior. Steaming preserves the crisp texture while reducing any cabbage-like intensity. Kohlrabi also performs excellently in stir-fries, soups, and gratins.

The leaves shouldn’t be overlooked culinarily. Young leaves can be used raw in salads, while mature leaves excel when sautéed, braised, or added to soups and stews. They pair particularly well with garlic, onions, and bacon or other smoked meats.

Traditional European preparations include kohlrabi schnitzel (sliced, breaded, and pan-fried), cream-based gratins, and pickled preparations for winter storage. Asian cuisines often feature kohlrabi in stir-fries and curry dishes, where its ability to absorb flavors while maintaining texture makes it particularly valuable.

Harvesting Guide

Proper harvest timing is crucial for kohlrabi quality, as bulbs can quickly become woody and inedible if left too long in the ground. Most varieties are ready for harvest 55-75 days from seed, but size and texture provide better indicators than calendar dates.

Harvest bulbs when they reach 2-4 inches in diameter, depending on variety. At this size, they should feel firm and heavy for their size, with smooth, unblemished skin. The optimal harvest window typically spans 1-2 weeks, after which bulbs begin developing a fibrous, woody texture even if they remain visually appealing.

Early morning harvesting often provides the crispest, most flavorful bulbs, as plants are fully hydrated from overnight moisture. Use a sharp knife to cut the bulb at soil level, leaving roots in the ground to decompose naturally.

Leaves can be harvested throughout the growing season, either individually as needed or all at once during bulb harvest. Young leaves are tender enough for raw consumption, while older leaves require cooking but offer more robust flavor.

Fresh kohlrabi stores well in the refrigerator for 2-4 weeks when kept in plastic bags or the crisper drawer. Remove leaves before storage to prevent moisture loss from the bulb. For longer storage, kohlrabi can be blanched and frozen, though texture changes make frozen kohlrabi best suited for cooked applications.

Common Problems & Solutions

Kohlrabi shares many pest and disease challenges with other brassica crops, though it generally shows good resistance to most issues when grown under appropriate conditions.

Flea beetles pose the most common early-season threat, creating numerous small holes in young leaves that can severely weaken plants. Row covers provide effective protection during the vulnerable seedling stage, or apply beneficial nematodes to soil before planting for biological control.

Cabbage worms and imported cabbageworms can defoliate plants rapidly. Hand-picking provides control in small gardens, while Bacillus thuringiensis (Bt) offers organic control for larger plantings. Regular inspection allows early intervention before populations become damaging.

Clubroot represents the most serious soil-borne disease threat, causing swollen, distorted roots and stunted growth. Prevention through crop rotation, soil pH management, and avoiding contaminated soil or tools provides the only effective control, as no chemical treatments exist for infected plants.

Splitting occurs when inconsistent watering causes rapid bulb expansion after dry periods. Maintain consistent soil moisture through mulching and regular irrigation schedules. Harvest bulbs promptly once they reach optimal size to prevent splitting from overmaturity.

Bolting (premature flowering) typically results from temperature stress or day-length changes. Choose bolt-resistant varieties for challenging seasons and provide consistent growing conditions. Once bolting begins, harvest immediately as bulb quality deteriorates rapidly.

Woody texture develops when bulbs grow too large or remain in the ground too long. Prevent this through timely harvesting and succession planting to ensure continuous supplies of young, tender bulbs.

Varieties & Cultivars

Early White Vienna remains one of the most reliable varieties for home gardeners, producing pale green bulbs ready for harvest in 55-60 days. This heirloom variety shows good heat tolerance and consistent performance across different growing conditions.

Early Purple Vienna offers similar characteristics to its white counterpart but with attractive purple-tinged skin. The flesh remains white regardless of exterior color, and many gardeners find the purple varieties slightly sweeter.

Gigante lives up to its name, producing massive bulbs up to 10 inches in diameter while maintaining good eating quality. This variety requires a longer growing season (75-80 days) but provides excellent storage characteristics for winter use.

Kolibri represents modern breeding focused on bolt resistance and heat tolerance. This hybrid variety performs exceptionally well in challenging conditions and produces uniform, tender bulbs in just 50-55 days.

Superschmelz translates to “super melting” in German, referring to its exceptionally tender texture even at large sizes. This variety can be harvested at various sizes without becoming woody, providing flexibility in harvest timing.

Quickstar offers the fastest maturation at just 38-45 days from transplant, making it ideal for short-season areas or quick succession crops. Bulbs remain small but provide excellent flavor and texture.

For organic growers, Azur Star and Delicacy White show particularly good resistance to common diseases and pests, reducing the need for interventions during the growing season.

FAQ Section

Can kohlrabi be grown in containers?

Yes, kohlrabi adapts well to container growing. Use containers at least 8-10 inches deep and 6-8 inches wide per plant. Choose compact varieties like Quickstar or Early Vienna types for best results in limited space.

Why are my kohlrabi bulbs woody and tough?

Woody texture typically results from harvesting too late, inconsistent watering, or excessive heat stress. Harvest bulbs when 2-4 inches diameter and maintain consistent soil moisture throughout the growing season.

Can I eat kohlrabi leaves?

Absolutely! Kohlrabi leaves are edible and nutritious, similar to collard greens or kale. Young leaves can be eaten raw in salads, while mature leaves are excellent when cooked. They’re actually higher in vitamins A and K than the bulbs.

How do I prevent my kohlrabi from bolting?

Choose bolt-resistant varieties, maintain consistent growing conditions, and avoid temperature stress. Plant at appropriate times for your climate and provide adequate water during hot weather. Once bolting begins, harvest immediately.

What’s the best way to store fresh kohlrabi?

Remove leaves and store bulbs in the refrigerator crisper drawer or in plastic bags for 2-4 weeks. Keep leaves separately and use within a few days. For longer storage, kohlrabi can be blanched and frozen for cooked applications.

Why aren’t my kohlrabi bulbs forming properly?

Poor bulb formation often results from overcrowding, excessive nitrogen fertilization, or unsuitable growing conditions. Ensure proper spacing (4-6 inches apart), avoid over-fertilizing with nitrogen, and maintain consistent moisture.

Can kohlrabi survive frost?

Yes, kohlrabi is quite cold-tolerant and can withstand light frosts down to about 25°F. In fact, light frost often improves flavor by converting starches to sugars. Mature plants can tolerate temperatures as low as 20°F with some protection.

How often should I plant kohlrabi for continuous harvest?

For continuous harvest, plant new crops every 2-3 weeks from spring through late summer. This succession planting ensures a steady supply of tender, young bulbs since the harvest window is relatively narrow.

What pests are most problematic for kohlrabi?

Flea beetles and cabbage worms are the most common pests. Flea beetles attack young plants, while cabbage worms can defoliate mature plants. Row covers, Bt spray, and beneficial insects provide effective organic control methods.

Can I grow kohlrabi in partial shade?

Kohlrabi tolerates partial shade, especially in hot climates where afternoon shade can be beneficial. Aim for at least 4-6 hours of direct sunlight daily. In cooler climates, full sun produces the best bulb development.

How do I know when kohlrabi is ready to harvest?

Harvest when bulbs reach 2-4 inches in diameter and feel firm and heavy. The skin should be smooth and unblemished. If you can easily indent the bulb with your fingernail, it’s likely overripe and may be woody.

Can I save seeds from my kohlrabi plants?

Yes, but kohlrabi is biennial, meaning it flowers and produces seeds in its second year. In cold climates, you’ll need to overwinter plants indoors or in cold frames. Be aware that kohlrabi can cross-pollinate with other Brassica oleracea varieties like broccoli and cabbage.

Sources & References

• University of Minnesota Extension — Growing Kohlrabi in Home Gardens
• Clemson Cooperative Extension — Cole Crop Insect Pests
• USDA Plants Database — Brassica oleracea

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