How to grow kohlrabi
Overview
Kohlrabi is a cool-season brassica grown for its edible, swollen stem that develops just above ground level. It is a fast-growing, reliable crop that thrives in mild weather and requires consistent moisture for best results.
Varieties
- Purple Vienna — A classic purple-skinned variety with a crisp, white interior, popular in Australian gardens.
- White Vienna — A pale green-skinned variety with a mild, sweet flavour, ideal for early harvests.
- Kohlrabi 'Superschmelz' — A large, slow-bolting variety that can reach 10 cm in diameter without becoming woody.
Soil Preparation
Kohlrabi prefers a pH of 6.0–7.0 in well-drained, fertile soil. Enrich with well-rotted compost or manure before planting. Avoid heavy clay soils that can cause poor stem development.
Growing Guide
Plant kohlrabi in full sun in well-drained, fertile soil. Sow seeds 6 mm deep, 30 cm apart, or transplant seedlings at the same spacing. For a steady supply, sow small batches every 3–4 weeks. Keep soil consistently moist, especially as the stem begins to swell.
Sowing
Sow seeds 6 mm deep, 30 cm apart, directly into the garden or into punnets for transplanting. Germination takes 5–10 days. Thin seedlings to 30 cm apart. For best results, sow in cool weather.
Care
Feed kohlrabi with a balanced liquid fertiliser every 2–3 weeks during active growth. Keep soil consistently moist but not waterlogged; mulch to retain moisture and suppress weeds. No pruning needed, but remove any yellowing leaves to improve airflow.
Companion Planting
Kohlrabi grows well with beetroot, onions, and herbs like dill and mint. Avoid planting near other brassicas such as broccoli or cabbage to reduce pest pressure.
Common Pests & Risks
Cabbage white caterpillar, aphids, and flea beetle are common. Control caterpillars with Bacillus thuringiensis or netting. Use a strong water spray for aphids and apply diatomaceous earth for flea beetles. Rotate crops to reduce pest buildup.
Harvesting
Harvest kohlrabi when the swollen stem is 5–8 cm in diameter, before it becomes woody. Cut the stem at soil level and remove the leaves. The stem is the main edible part, but young leaves can also be eaten.
In the Kitchen
Kohlrabi can be eaten raw, sliced into salads, or cooked like a turnip. The stem has a crisp, apple-like texture. Store in the fridge for up to 2 weeks. Young leaves are also edible and can be used in stir-fries.
Troubleshooting
Yellow leaves: overwatering or nitrogen deficiency. Brown edges: inconsistent watering or heat stress. Small, woody stems: delayed harvest or poor soil. Bolting: caused by sudden heat or drought. Pests: use netting to protect from cabbage white caterpillars.