How to Grow Kohlrabi
Brassica oleracea var. gongylodes
Kohlrabi is a quick, cool-season brassica for full sun and moist, fertile, free-draining soil. Sow little-and-often from spring to late summer. Transplant promptly and keep growth even to prevent woody bulbs. Water regularly and mulch to retain moisture. Harvest when tennis-ball sized (or smaller for extra tenderness). Protect from flea beetle and caterpillars with fine mesh. Space closely for baby bulbs or wider for larger ones.
When to Start
Direct sow outdoors as soon as soil reaches 6°C — typically early to mid spring. Can also be started indoors 4 weeks earlier for a head start.
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Growth Stages
Approximate days from start
Care Essentials
- Light balanced feed at sowing. Needs consistent moisture.
- Quick-growing (8–10 weeks). Mild, sweet flavour — eat raw or cooked. Purple varieties are more ornamental.
Growing Conditions
- Min. soil temperature
- 6°C+
- Germination temperature
- 15–25°C
- Sow indoors
- —
- Transplant out
- —
- First harvest
- —
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Spacing & Planting
| Plant spacing | 20 cm |
| Row spacing | 30 cm |
| Sow depth | 0.5 cm |
| Mature height | 40 cm |
| Mature spread | 30 cm |
Fast crop; keep growing steadily to avoid woody bulbs.
Pests & Diseases
Pest Flea Beetle
Identification: Tiny round shot-holes peppered across leaves, small shiny black beetles that jump when disturbed
- Cover with fine insect mesh immediately after sowing or planting
- Water regularly to encourage fast growth through vulnerable stage
- Sticky traps placed near plants
- Pyrethrum-based spray as a last resort
Pest Cabbage Root Fly
Identification: Wilting plants despite adequate watering, white maggots around roots when lifted
- Brassica collars around stems at planting to prevent egg-laying
- Fine insect mesh over the crop
- Companion plant with strong-scented herbs
- No effective chemical treatments available to home gardeners
Pest Cabbage White Caterpillars
Identification: Large ragged holes in leaves, green or yellow-black caterpillars visible, clusters of yellow eggs on leaf undersides
- Cover with insect mesh from planting
- Hand-pick caterpillars and eggs regularly
- Bacillus thuringiensis (Bt) spray
- Limited options for edible crops
Disease Clubroot Plasmodiophora brassicae
Symptoms: Stunted growth, wilting in warm weather despite moist soil, swollen and distorted roots
Treatment: No cure once established. Remove and destroy affected plants. Do not compost.
Prevention: Lime soil to pH 7.0-7.5. Practice strict 4-year brassica rotation. Improve drainage. Start plants in modules with clean compost.
Disease Downy Mildew Hyaloperonospora parasitica
Symptoms: Yellow patches on upper leaf surfaces with grey-white fuzzy growth underneath
Treatment: Remove affected leaves promptly. Improve air circulation.
Prevention: Space plants well for airflow. Avoid overhead watering. Water in the morning so foliage dries quickly.
Growing Conditions
| Min. soil temperature | 6°C |
| Germination temperature | 15–25°C |
| Base growth temperature | 4°C |
| Min. daylength to start | 9h |
| Photoperiod sensitivity | long day |
Frequently Asked Questions
- How far apart should I plant Kohlrabi?
- Plant Kohlrabi 20cm apart with 30cm between rows.
- When can I harvest Kohlrabi?
- Kohlrabi is ready to harvest approximately 35 days after transplanting.
- Is Kohlrabi frost hardy?
- Kohlrabi is classified as Hardy.
