Kohlrabi Grow Guide for South African Conditions

Kohlrabi is a compact, quick-growing brassica for cool-season vegetable gardens. The crisp swollen stem develops above the soil and is best harvested young, when it is sweet, juicy and tender enough for salads, slaws, roasting or stir-fries.

This guide is written for Kohlrabi Purple Vienna and focuses on reliable South African timing, even growth and early harvesting before heat or water stress affects quality.

Quick Grow Facts

• Plant type: Cool-season brassica vegetable, grown as an annual.
• Botanical name: Brassica oleracea Gongylodes Group.
• Best sowing time: Late summer through autumn in most regions, with a late-winter or early-spring window in cooler districts.
• Position: Full sun in cool weather; light afternoon shade can help as temperatures rise.
• Sow depth: About 6-12 mm.
• Spacing: Thin Purple Vienna plants to about 10-15 cm apart, with rows around 30 cm apart.
• Germination: Keep the seedbed evenly moist; cool to mild conditions support sturdy seedlings.
• Harvest: Pick the swollen stems at about 5-8 cm across while they remain tender.

When To Sow In South Africa

Winter-rainfall regions

In the Western Cape, sow from late summer into autumn for winter growth. Kohlrabi enjoys cool conditions, but wet soil must still drain freely. A second sowing can be made towards the end of winter where plants will mature before hot spring weather.

Summer-rainfall inland regions

On the Highveld and in the Free State, North West and cooler inland districts, late summer and autumn are the easiest windows. Irrigate through dry winter weather and use insect netting or securely anchored row cover where young brassicas are under pressure. Late-winter sowings are possible if the crop can mature before strong heat returns.

Warm coastal and subtropical regions

Use the coolest months along the KwaZulu-Natal coast and in warm, humid areas. Give plants good airflow and avoid keeping foliage wet overnight. Fast, uninterrupted growth is important because warm spells can reduce tenderness.

Hot, dry and Lowveld regions

Plan for a winter crop. Sow only once nights and soil have cooled, maintain reliable irrigation and protect young plants from drying wind. The aim is to harvest before intense spring heat arrives.

How To Sow Kohlrabi

1. Prepare fertile, fine soil in a garden bed, raised bed or seedling tray.
2. Sow 6-12 mm deep and keep the seedbed evenly moist.
3. Thin direct-sown seedlings early, or transplant young plugs before they become root-bound.
4. Set transplants at the same depth they grew in their cells; do not bury the developing stem.
5. Water plants in well and protect them from strong sun and wind while they establish.

Soil, Water And Feeding

Kohlrabi performs best in fertile, moisture-retentive soil that drains freely. Incorporate mature compost before planting. Avoid excessive nitrogen, which can produce lush leaves without improving the swollen stem.

• Water deeply enough to wet the root zone and keep moisture consistent.
• Mulch established plants lightly in dry regions, keeping material away from the stem.
• Remove weeds while they are small so shallow cultivation does not damage roots.
• Rotate kohlrabi away from cabbage, broccoli, kale and other brassicas where practical to reduce recurring pest and disease pressure.

Pest Protection

Young brassicas are vulnerable to cutworms, snails, slugs, flea beetles and leaf-eating caterpillars. Inspect both sides of leaves regularly. Fine insect mesh can be useful, but it must be secured before pests enter and lifted enough that foliage is not compressed.

Check plants for aphids and signs of stress. Correct identification matters before treatment, especially because beneficial insects may already be controlling a small pest population.

Common Mistakes To Avoid

• Sowing too late: Heat can make stems tough, fibrous or bitter.
• Irregular watering: Moisture stress slows growth and can cause splitting.
• Overcrowding: Plants need enough space and light to form even swollen stems.
• Burying the stem: Kohlrabi forms above the soil; do not earth it up like a root crop.
• Harvesting oversized stems: Purple Vienna is at its best when picked young rather than left for maximum size.

Harvesting And Kitchen Use

Harvest when the swollen stem is roughly 5-8 cm across. Cut it at soil level, remove the leaves and peel any firm outer skin before eating. The flesh can be sliced raw, grated into slaw, roasted, steamed or added to stir-fries. Tender young leaves can also be cooked like other brassica greens.

Shop Kohlrabi Seeds

• Kohlrabi Purple Vienna Seed

Explore more cool-season crops in our vegetable seed collection and winter vegetable seeds.