Kohlrabi – Growing Guide

Overview

• Name: Kohlrabi
• Botanical Name: Brassica oleracea var. gongylodes
• Plant Family: Brassicaceae (Mustard Family)
• Native to: Europe, specifically the Mediterranean region

Description

Kohlrabi is a biennial vegetable most often grown as an annual for its swollen, globe-like stem, which is smooth, firm, resembles a turnip in appearance, and forms just above the soil surface. This enlarged stem—commonly called a “bulb,” though technically a thickened portion of the stem—can grow up to 10 cm (4 in) in diameter and may be green, white, or purple in color, depending on the variety. All kohl rabi bulbs, regardless of their external color, are white or pale green inside. The kohlrabi bulb has a crisp texture and pleasantly mild sweetness, and is are often compared to a sweeter, milder version of broccoli stems or turnips.

The plant typically reaches 40–50 cm (16–20 in) in height with a similar spread. It has long, bluish-green waxy leaves with long petioles (leaf stems), which sprout radially as a rosette from the sides of the bulb. These leaves are also edible and can be cooked as leafy greens. If left to mature into its second year, kohlrabi produces a tall flowering stalk with small, yellow, four-petaled flowers characteristic of the Brassica family. These flowers develop into seed pods containing small, round seeds (1–2 mm in diameter) that are dark brown to black.

Sometimes referred to as turnip-rooted cabbage or German cabbage, kohlrabi originated in Europe. The plant is highly versatile in the kitchen, used in both raw forms, such as salads and slaws, and cooked preparations, where it retains its crispness and mild flavor. Kohlrabi thrives in cool weather and can be grown successfully in a variety of soil types, making it a popular choice for home gardeners.

Interesting Facts

1. Kohlrabi’s name comes from the German words “kohl” (cabbage) and “rübe” (turnip), reflecting its cabbage family heritage and bulbous shape. Despite the name, it is not a true turnip or root vegetable, but a swollen stem.
2. Kohlrabi is highly nutritious, containing more vitamin C by weight than oranges. It also contains dietary fiber, phytonutrients for digestive health, and beneficial compounds like glucosinolates, similar to broccoli and kale, which support immune function and overall well-being.
3. Historical records trace the cultivation of kohlrabi to 16th-century Europe, where it was prized for its reliable yield in cool climates. Over time, it spread throughout the continent, notably gaining popularity in German-speaking countries. Kohlrabi also reached other parts of the world, particularly Asia, and is now widely used in cuisines across northern India, where it appears in salads and curries.
4. Kohlrabi is useful in sustainable agriculture because it matures quickly and can be grown in compact spaces, making it an excellent choice for spring and autumn gardens.. Its shallow root system means it can coexist with plants that have deeper roots, optimizing the use of growing spaces and maximizing yields in smaller home gardens or commercial urban farms.
5. The crisp, sweet flesh of kohlrabi has a delicate peppery hint, making it a refreshing raw snack or salad ingredient. The leaves can also be eaten and prepared similarly to collard greens. Different varieties, such as ‘Early White Vienna’ or ‘Purple Vienna,’ offer subtle differences in color and taste.

Basic Growing Information

Kohlrabi is a cool-season crop that thrives in cool climates, in temperatures ranging from 10–24°C (50–75°F), with the optimal range around 15–20°C (59–68°F). The plants can tolerate mild frosts better than many other vegetables and withstand brief dips in temperature without severe damage. However, prolonged exposure to temperatures below 7°C (45°F) will cause them to bolt.

Plants can be grown in early spring and autumn to take advantage of the cooler weather that promotes tender, bulbous stems. In springtime, seeds and seedlings can be planted outdoors 1 to 2 weeks before the last frosts. For autumn plantings, time seed sowing or seeding transplanting so that plants mature no more than 2 to 3 weeks after the first frosts appear.

In warm climates, or areas with hot summers, kohlrabi should be planted in time for an autumn harvest, during the growing period when daytime temperatures remain moderate, as plants may struggle under high heat.

• Purple varieties (e.g., ‘Purple Vienna’) often take slightly longer to mature and can be somewhat hardier (more cold-tolerant), making them suitable for later sowings and winter harvest, or overwintering in milder regions.
• Green or white-skinned varieties (e.g., ‘Early White Vienna’) typically mature faster (are early maturing) and are more commonly chosen for spring and summer sowing.

Kohlrabi, like other Brassicas, thrives in well-drained, fertile soil with consistent moisture and requires at least six hours of sunlight for optimal growth.

• Sun Requirements: Full sun (at least 6 hours daily), some  varieties will also grow in partial shade in summer
• Water Requirements: Moderate (regular watering, keeping soil evenly moist)
• Soil Types and Properties: Prefers rich, fertile, well-draining loamy soil rich in organic matter
• Soil pH: Optimal range is 6.0–7.5
• Pot Size for Container Growing: 20–25 cm diameter (8–10 in)

Planting

• Best Time to Plant:
  • Climates with freezing winters: Sow seeds indoors 4-6 weeks before the last frost date or directly outdoors in early spring as soon as the soil can be worked. For an autumn harvest, plant about 6-8 weeks before the first frost.
  • Climates with milder winters: Sow seeds in late winter to early spring and again in autumn

Note: Check gardening calendars for the best planting times in your location

• Spacing: Plant seeds or seedlings about 15–20 cm (6–8 in) apart with 30–40 cm (12–16 in) between rows
• Seed Sowing Method: Sow seeds directly into the ground or start in seed trays for transplanting
• Seed Sowing Depth: 1 cm (1/2 in) deep
• Time to Harvest: Typically 7-10 weeks when planted from seed, depending on the variety.
• Mature Height/Spread: 30–45 cm (12–18 in) tall, 30–45 cm (12–18 in) wide
• Grown From: Seeds

Care and Maintenance

• Watering Tips: Keep soil consistently moist, especially during stem enlargement. Avoid waterlogging, as overly saturated soil can lead to rot and diminish the plant’s vigor. Water at the base to avoid wetting the foliage.
• Fertilization: Apply a balanced fertilizer at planting followed by side-dressing of fertilizer halfway through the growing season, or when when plants reach about half their mature size. Avoid overfertilizing as too much nitrogen too early can promote excessive leaf growth at the expense of bulb development.
• Pruning: Not necessary, but thinning the seedlings to the correct spacing when the plants have 3-4 true leaves is crucial to allow the bulbs to develop properly. Remove yellowing or damaged lower leaves as the stem enlarges to promote airflow and reduce disease risk.
• Support: Not required, as the bulbs develop near ground level and the leaves are relatively light. If grown in windy conditions or loose soil, a small stake or protective barrier may be used. Maintain a weed-free environment, as vigorous weeds can crowd kohlrabi and destabilize its shallow root system.
• General care and maintenance Kohlrabi has a shallow root system, and therefore needs regular watering to prevent the plants from drying out. Use mulches to conserve soil moisture and keep the soil cool. Maintain a weed-free environment, particularly when plants are young, as vigorous weeds can crowd kohlrabi and destabilize its shallow root system. Take care to avoid damaging the plant’s root system when weeding. 

Growing Difficulty

• Easy to moderate, suitable for both novice and experienced gardeners.

Growing Tips

• Kohlrabi prefers cooler temperatures and can become woody in too much heat.
• Mulch around the plants to help retain soil moisture and control weeds.
• To prevent woody, fibrous stems, avoid letting kohlrabi grow overly large; harvest when bulbs reach about 5–8 cm (2–3 in) in diameter.
• Consistent moisture, even during cooler weather, promotes tender growth.
• Succession planting every few weeks ensures a continuous harvest rather than an all-at-once glut of mature bulbs.
• Protect young seedlings from flea beetles and other early pests by using row covers. Removing covers is typically unnecessary since kohlrabi don’t need to be pollinated as they are grown for the stems.
• Rotate kohlrabi with non-Brassica crops in the following season to minimize disease and pest buildup in the soil. Avoid planting where other Brassicas (like cabbage or broccoli) grew in the previous year. A break of at least two to three years helps disrupt pest and disease life cycles.

Companion Plants

• Good companion plants include: Beets, onions, cucumbers, and herbs like mint or dill
• Avoid planting near: Tomatoes, strawberries, or other Brassicas (to reduce competition and pest pressure, as they are from the same family and may share pests and diseases)

Common Pests and Diseases

• Pests:
  • Flea beetles: Use row covers and maintain weed-free beds; apply insecticidal soap if infestation is severe
  • Cabbage loopers: Handpick caterpillars, use Bacillus thuringiensis (Bt) sprays if needed
  • Aphids: Wash off with water or use insecticidal soap; encourage beneficial insects like ladybugs

• Diseases:
  • Clubroot: Practice crop rotation and ensure good drainage; amend soil with lime if pH is too acidic
  • Black rot: Remove infected plants promptly; rotate with non-Brassica crops
  • Downy mildew: Improve airflow, avoid overhead watering, and consider resistant varieties

Harvesting

Harvest Time: Kohlrabi is ready to harvest and are at their sweetest, with a mild flavor and crunchy texture when the swollen stems reach 5–8 cm (2–3 in) in diameter, between golf-ball and tennis-ball size, typically 6–8 weeks after sowing the seeds. If left too long, the bulbs may become tough, woody and bitter and lose their desirable flavor. Young leaves can be harvested during the growing season prepared in the same way as kale.

Harvesting Tips:

• Use a sharp knife to cut the stem below the bulb just above soil level. Remove the leaves and store them separately if you plan to eat them as greens.
• Bulbs can easily turn woody in hot, dry weather, and spring-planted kohlrabi harvested in summer is more likely to become fibrous if allowed it to become over-mature.
• Autumn-harvested kohlrabi can be allowed to grow a bit bigger without losing quality.
• Some kohlrabi varieties tolerate cold weather in the garden without splitting. If you plan to harvest well into autumn, select a cultivar noted for its strong “field holding” ability.

Storage: If kept at about 2°C (36°F) and 95% humidity—conditions often limited to commercial facilities—kohlrabi bulbs can store for several months. In most home refrigerators, however, they maintain quality for around two weeks. Placing unwashed bulbs in a perforated bag (one with air holes) helps retain moisture without trapping excess condensation. During autumn, some hardier varieties can be held in a cool but frost-free space for extended periods, or left in the ground as long as temperatures remain moderate. In both cases, regularly check for splitting and plan to use kohlrabi when it’s still crisp and flavorful.

Propagation

• Propagated by seed. Kohlrabi does not typically produce seeds in its first year, as it is biennial and produces seeds in its second year.

Culinary Uses

Kohlrabi is a versatile vegetable that can be eaten raw in salads or as a snack. It is also great when steamed, roasted, or added to soups and stews. Its crisp texture makes it a good addition to many dishes.

• When eaten raw, the bulb can be sliced or julienned and added to salads, slaws, or crudités. The sweet and slightly peppery flavor pairs well with tangy dressings, creamy dips, or light vinaigrettes.
• Steamed, roasted, or sautéed kohlrabi becomes sweeter and can be treated like turnips or potatoes.
• In soups and stews, it lends a mild cabbage-like note, thickening broths as it cooks.
• The leaves, similar to collard greens, are delicious when lightly steamed or sautéed with garlic and onions.
• For pickling enthusiasts, thin kohlrabi slices can be brined in vinegar-based solutions to create crisp, tangy snacks or side dishes.
• A popular method in many Asian cuisines involves stir-frying julienned kohlrabi with spices and herbs, resulting in a flavorful, tender-crisp meal.

Overall, kohlrabi’s adaptability makes it a welcome ingredient across diverse culinary traditions.

In conclusion, kohlrabi is an easy-to-grow, cool-season vegetable offering a unique flavor and remarkable versatility in the kitchen. With basic care, attention to planting times, and mindful harvesting, gardeners can enjoy the tender, sweet bulbs and leafy greens of this distinctive Brassica crop.

References

• University of Minnesota Extension. (n.d.). Growing Kohlrabi. https://extension.umn.edu/vegetables/growing-kohlrabi
• Kohlrabi | Diseases and Pests, Description, Uses, Propagation. Plant Village. https://plantvillage.psu.edu/topics/kohlrabi/infos
• Royal Horticultural Society. (n.d.). Kohl rabi. https://www.rhs.org.uk/vegetables/kohl-rabi