Kohlrabi, often dubbed the 'turnip cabbage', is an eye-catching addition to any garden. This quirky vegetable resembles an alien creation, making it a fun choice for cultivation.
A blend of broccoli, turnip, and apple, kohlrabi (Brassica oleracea var. gongylodes) features long leafy stems surrounding a swollen stem, known as a bulb. These bulbs grow rapidly above the soil with minimal care, thriving as cool-season crops that can be planted early in the year or later when the weather cools.
Crisp and refreshing, kohlrabi is packed with vitamins C and A, potassium, iron, and calcium. Both its stems and greens are edible, enhancing meals with a peppery kick. Not only is it resilient against frost, but it also tolerates drought better than other brassicas. Depending on the variety, you can harvest kohlrabi from summer through winter, making it an adventurous choice for your garden.
Kohlrabi thrives in cooler gardening seasons.
Janey Goulding, an assistant editor with extensive gardening experience, shares her insights on successfully growing kohlrabi.
Optimal Conditions for Kohlrabi Growth
To successfully grow kohlrabi, ensure it receives plenty of sunlight, regular watering, and adequate spacing. These plants are relatively easy to cultivate and don't require intensive soil preparation. Aim for a location that offers at least six hours of sunlight daily and a moist, well-draining soil enriched with compost. While kohlrabi can adapt to various soil types, it prefers a pH of 6-7. Using a raised bed can improve drainage, provided there's enough depth for the roots.
Kohlrabi is forgiving and doesn't have strict requirements. However, avoid planting it in the same spot as previous brassicas to prevent nutrient issues. Companion planting with cucumbers, beets, chives, and onions can enhance growth.
Raised beds provide ideal conditions for kohlrabi growth.
Timing and Techniques for Growing Kohlrabi
You can start kohlrabi seeds in spring or summer, aligning with the cool-season preference of this vegetable. They appreciate a warm start, especially if started indoors, before transitioning to cooler conditions for maturation. While kohlrabi improves with a light frost, protecting young plants with blankets or tunnels is wise during unpredictable cold snaps.
For spring planting, sow seeds outdoors once the soil temperature exceeds 45˚F. Indoors, ensure they can be transplanted to benefit from cooler spring weather. Alternatively, summer planting allows for flourishing before fall. Depending on your region and chosen varieties, sowing can occur from February to August. Kohlrabi thrives in USDA zones 3-9 and prefers temperatures between 60-70˚F.
There are two primary kohlrabi types: green and purple. Green varieties are suitable for spring sowing, while purple types thrive in high summer. Purple kohlrabi is hardier and can be harvested into winter. Notable early varieties include 'Viennese Early White', 'Olivia', and 'Grand Duke', while options for fall harvests include 'Purple Vienna' and 'Gigante'.
Purple varieties of kohlrabi include 'Purple Vienna' and 'Kolibri'.
Planting Kohlrabi from Seeds
Starting kohlrabi from seeds is simple. Prepare your soil with compost or aged organic matter before planting. Choose whether to start seeds indoors or outdoors based on your desired harvest timeline and weather conditions. Follow these steps for successful kohlrabi planting:
- For indoor sowing, use modules of moist compost with two seeds per cell. Expect germination in 10-14 days.
- After four weeks, harden off seedlings before transplanting when they reach 2 inches tall.
- If sowing directly outdoors, plant seeds half an inch deep, spaced about 2 inches apart. Cover lightly with soil and water in.
- For outdoor sowing, use covers to protect from frost and pests.
- Thin seedlings once the first true leaves appear, ensuring remaining plants are spaced 8-12 inches apart.
- Make successive sowings every three weeks from March to August for continuous harvests.
Thin kohlrabi seedlings as they grow to ensure proper spacing.
Container Gardening for Kohlrabi
Growing kohlrabi in containers is feasible. Ensure you provide good light, moisture, and ample space. Use large containers—at least 15 inches deep—to accommodate root growth. Opt for materials that retain moisture, like plastic, or add mulch to help.
Monitor moisture levels closely, as kohlrabi can tolerate some drought but prefers consistent hydration for optimal flavor. Grow them in sunny spots but offer partial shade during heat waves. Limit containers to one kohlrabi per pot for best results, and choose quicker-maturing varieties like 'Grand Duke' or 'Kolibri'.
Use deep, well-nourished containers for successful kohlrabi growth.
Maintaining Healthy Kohlrabi
Once established, kohlrabi is easy to care for. Regular watering is crucial, requiring about an inch of rain weekly. Balanced moisture prevents crops from becoming woody or bitter. Apply mulch to retain moisture and maintain humidity during warm spells. Fertilize every few weeks to encourage growth.
Keep weeds at bay by removing them promptly while avoiding disturbance to young plant roots. Maintaining adequate spacing will help prevent overcrowding and competition for nutrients.
Stay vigilant against weeds without disturbing root systems.
Common Issues and Solutions
While kohlrabi can face challenges similar to other brassicas, they tend to be more resilient. Here are some common issues and how to address them:
- Clubroot: Look for stunted growth and swollen roots. Increase soil alkalinity with lime and ensure good drainage.
- Aphids: Check for yellow or distorted leaves. Control them by introducing beneficial insects or using soapy water.
- Cabbage worms: Remove visible caterpillars by hand or use organic insecticides.
- Powdery mildew: Ensure good airflow and select resistant varieties to reduce risk.
- Cabbage rootfly: If you see wilting plants and maggots, use mesh or nematodes to protect roots.
Address pest damage promptly to protect your crop.
Harvesting Your Kohlrabi
Harvest kohlrabi 45-60 days after planting, ideally when the bulbs are 2-3 inches in diameter. Both the bulb and greens are edible, and kohlrabi is at its best when eaten fresh. Store in the fridge for a week or two if necessary. Enjoy it raw or cooked, whether sliced, diced, or mashed.
Harvest kohlrabi as soon as six weeks after planting for the best flavor.
Frequently Asked Questions
Why hasn't my kohlrabi formed a bulb?
If the bulb isn't developing, it may be due to overcrowding. Ensure plants are spaced 6-9 inches apart, and check for exposure to extreme temperatures or inadequate watering.
Why does my kohlrabi taste woody or have cracks?
Woody bulbs usually indicate that the kohlrabi was left in the ground too long. Harvest at 2-3 inches. Inconsistent watering or excessive nitrogen can also contribute to these issues.
Can I grow kohlrabi from cuttings?
While you can experiment with cuttings, seed propagation is generally more reliable. If attempting cuttings, ensure they have a few leaves and root them in water before transplanting.
