Botanical Classification
Kohlrabi, scientifically classified as Brassica oleracea var. gongylodes, is a member of the Brassicaceae family, which includes cruciferous vegetables like cabbage, broccoli, and kale. This cultivar is a type of cabbage, but unlike head-forming varieties, it develops a swollen, bulb-like stem just above the soil. It shares its species with other Brassica oleracea crops, all derived from wild cabbage native to coastal Europe, but its unique stem morphology distinguishes it, earning it the nickname “turnip cabbage” despite not being a true turnip.
Origin and History
Kohlrabi likely originated in Northern Europe, with cultivation records dating back to the 1st century AD in Roman texts, though it became more prominent in the Middle Ages, particularly in Germany and Central Europe. Its name, derived from the German “kohl” (cabbage) and “rabi” (turnip), reflects its appearance and heritage.
Bred for its edible stem, kohlrabi was valued for its versatility and ability to grow in cooler climates. By the 19th century, it spread across Europe and Asia, and today it is grown globally, especially in temperate regions, appreciated for its mild flavor and crisp texture.
Identifying Characteristics
Kohlrabi is characterized by its bulbous, swollen stem, which grows just above ground and resembles a turnip, typically 2–4 inches in diameter. The stem can be pale green, purple, or white, depending on the variety, with smooth, edible skin. Leafy stalks with dark green leaves sprout from the bulb, resembling broccoli or kale leaves, and are also edible. The flesh inside the bulb is crisp, white, and juicy, with a texture similar to a radish or apple, making it distinct from head cabbages.
Taste
Kohlrabi has a mild, sweet flavor with a subtle peppery note, reminiscent of broccoli stems or radishes but less pungent. Its crisp, juicy texture is refreshing when raw, with a slight crunch that softens when cooked, developing a tender, sweeter profile.
The leaves taste similar to kale or collard greens, with a mild bitterness. Its delicate flavor makes it versatile, pairing well with both bold seasonings and light dressings, appealing to those who enjoy subtle cruciferous tastes.
Seasons/Availability
Kohlrabi is a cool-season crop, thriving in temperatures between 40°F and 75°F (4°C–24°C), and is typically available in spring (April–June) and fall (September–November) in the Northern Hemisphere. It tolerates light frost, which can enhance sweetness, but bolts in extreme heat.
Its short growing cycle allows multiple harvests in a season, and it’s commonly found in farmers’ markets, specialty grocers, and supermarkets during peak seasons, with some year-round availability in regions with mild climates or greenhouse production.
Culinary Uses
Kohlrabi is highly versatile, with both its bulb and leaves used in a variety of dishes. The bulb can be eaten raw, peeled and sliced into salads, slaws, or sticks for dipping, where its crisp texture shines. Cooked, it can be roasted, steamed, sautéed, or mashed, often paired with butter, garlic, or herbs to highlight its sweetness.
In Central European cuisines, it’s used in soups, stews, or gratins, while in Asian dishes, it’s stir-fried or pickled. The leaves are cooked like kale or spinach, added to soups, or sautéed as a nutritious side dish.
Nutritional Value
Kohlrabi is a low-calorie, nutrient-dense vegetable, providing about 35 calories per cup of raw bulb. It is an excellent source of vitamin C, an antioxidant that supports immune health and collagen production, and a good source of dietary fiber for digestive health. It also offers vitamin B6, potassium, and magnesium, contributing to energy metabolism and heart health.
As a cruciferous vegetable, it contains glucosinolates, compounds linked to potential cancer-fighting properties, and antioxidants that reduce inflammation. The leaves provide additional vitamins A and K, enhancing its nutritional profile.
Cultivation of Kohlrabi (Turnip Cabbage)
- Climate Requirements: Kohlrabi thrives in cool, temperate climates with temperatures between 40°F and 75°F (4°C–24°C). It tolerates light frost, which enhances sweetness by converting starches to sugars, but prolonged exposure below 32°F (0°C) can damage plants. High temperatures above 80°F (27°C) may cause bolting or woody bulbs, making it ideal for spring or fall planting in most U.S. regions, targeting harvests in April–June or September–November.
- Soil Preferences: This crop prefers fertile, well-drained loamy soil with a pH of 6.0–7.5. Incorporate organic matter, such as compost or aged manure, to boost soil fertility and improve moisture retention. Good drainage prevents root issues, and a neutral pH ensures nutrient availability, supporting the development of tender, juicy bulbs and healthy leaves.
- Planting Time: In the U.S., sow kohlrabi seeds in early spring (February–March) for a spring harvest or in late summer (July–August) for a fall harvest. Seeds can be sown directly in the ground when soil temperatures are 50°F–75°F (10°C–24°C) or started indoors 4–6 weeks before transplanting. Transplant seedlings when they are 3–4 inches tall to minimize transplant shock.
- Seed Selection: Choose high-quality seeds of kohlrabi varieties like ‘White Vienna’, ‘Purple Vienna’, or ‘Kossak’ for disease resistance, uniform bulb size, and flavor. Select varieties suited to your climate and desired harvest time (e.g., early or storage types). Fresh seeds from reputable suppliers ensure high germination rates, as kohlrabi seeds lose viability over time.
- Spacing and Planting: Space plants 6–8 inches apart in rows 12–18 inches apart to allow bulbs to develop without crowding. Sow seeds ¼–½ inch deep or plant transplants at the same depth as their nursery pots, firming soil around roots. Proper spacing ensures adequate light and airflow, promoting round, tender bulbs and reducing disease risk.
- Watering Needs: Provide consistent moisture, delivering 1–1.5 inches of water per week, adjusted for rainfall. Kohlrabi requires even watering to maintain juicy, tender bulbs, as drought stress can lead to woody or cracked bulbs. Use drip irrigation or soaker hoses to keep soil moist without wetting foliage, minimizing fungal diseases.
- Fertilization: Kohlrabi is a moderate feeder, requiring a balanced fertilizer (e.g., 10-10-10) at planting to support early growth. Side-dress with a nitrogen-rich fertilizer, such as fish emulsion or compost tea, 2–3 weeks after planting to promote bulb and leaf development. Avoid over-fertilizing, as excess nitrogen can result in excessive leaf growth at the expense of bulb size.
- Pest Management: Monitor for pests like flea beetles, cabbage worms, and aphids, which can damage bulbs and leaves. Use floating row covers to protect young plants, hand-pick caterpillars, or apply organic controls like neem oil or Bt (Bacillus thuringiensis). Companion planting with herbs like dill or attracting beneficial insects like ladybugs can help control pest populations naturally.
- Disease Control: Kohlrabi is susceptible to fungal diseases such as clubroot, downy mildew, and black rot, especially in wet conditions. Practice crop rotation every 2–3 years, maintain soil pH above 6.0, and ensure good drainage to reduce disease risk. Remove infected plant debris and choose disease-resistant varieties, using organic fungicides only if necessary.
- Weed Control: Keep the growing area weed-free to reduce competition for nutrients, water, and light. Hand-weed or hoe regularly, particularly during early growth. Apply organic mulch, such as straw or grass clippings, to suppress weeds, retain soil moisture, and regulate temperature, supporting healthy bulb and root development.
- Support and Pruning: Kohlrabi’s low-growing, bulbous structure doesn’t require staking, as plants remain stable. Remove yellowing or damaged lower leaves to improve airflow and reduce pest and disease risks. Minimal pruning is needed, but trimming older leaves can encourage tender bulb growth and maintain plant health, especially for continuous harvests.
- Harvesting: Harvest kohlrabi when bulbs are 2–4 inches in diameter, typically 40–60 days after planting, depending on the variety. Cut the bulb just below the swollen stem, leaving leaves intact if edible. Smaller bulbs are tenderer for raw use, while larger ones suit cooking or storage. Harvest leaves separately if young and tender, ideally in the morning for optimal freshness.
- Post-Harvest Care: Store kohlrabi bulbs in a cool, humid environment (32°F–40°F, 0°C–4°C) with 90–95% humidity for up to 2–3 months. Remove leaves before storing bulbs to prevent moisture loss, and wrap in plastic or store in perforated bags. Leaves can be stored separately for 1–2 weeks. Stagger plantings every 1–2 weeks during the planting season for continuous harvests.