When to plant Kohlrabi in Subtropical Australia

Subtropical zone — applies to Brisbane, Gold Coast, Sunshine Coast, Coffs Harbour, Lismore and similar areas. Growing elsewhere? Temperate · Cool · Tropical · Arid.

Sow kohlrabi direct from March to September, dropping seed about 6 mm deep straight into a well-prepared bed. It is quick for a brassica, germinating in just 6–12 days and swelling to a harvestable bulb in 55–70 days, which suits the mild subtropical winter perfectly. Thin or space plants 10–20 cm apart in rows 30–40 cm wide so each stem can form a round, tender bulb above the soil. In Brisbane and Coffs Harbour gardens this autumn-to-spring window keeps kohlrabi out of the humid summer heat that makes brassicas bolt and toughen.

Sowing calendar — subtropical zone

Green months are your sowing window: March to September.

Growing notes

Kohlrabi is one of the friendliest brassicas for the subtropics because it grows fast and matures before the worst heat and pest pressure arrive. Sow it into the cooler half of the year, keep the soil consistently moist and reasonably rich, and the swollen stems stay crisp and mild. Grow it in full sun and sow small batches every few weeks for a steady supply rather than a glut.

The key failure mode is a woody, cracked or stringy bulb, and it comes from stress. Irregular watering, a check in growth, or leaving bulbs too long past size all turn the flesh fibrous. The fix is even moisture and timely harvest: pick when bulbs reach around 6 to 8 cm across, roughly the size of a tennis ball, rather than waiting for them to get bigger, since larger bulbs toughen fast.

As a brassica, kohlrabi still draws the usual chewers. Cabbage white caterpillars, aphids and flea beetle can all riddle the leaves in a warm Lismore garden, and while the bulb is the prize, badly eaten foliage stunts it. Cover the bed with fine exclusion netting from sowing to keep cabbage moths off, and hose or squash aphid colonies early. A quick-growing crop like this outruns most trouble if you stay on top of watering and pick on time.

Kohlrabi at a glance

Common questions

When should I sow kohlrabi in the subtropics?

Sow direct from March to September, through the cooler frost-free months. This keeps the crop out of the humid summer heat that makes brassicas bolt and turn tough. Small successive sowings give a steady harvest.

Why is my kohlrabi woody and cracked?

That is stress from irregular watering or leaving the bulb too long. Keep the soil evenly moist and harvest when bulbs are about 6 to 8 cm across, around tennis-ball size, rather than letting them grow larger. Even growth keeps the flesh crisp and mild.

How do I stop caterpillars eating my kohlrabi?

Cover the bed with fine exclusion netting from sowing to keep cabbage moths from laying on the leaves. Check under foliage and squash any caterpillars you find, and hose off aphid colonies early. Protecting the leaves keeps the bulb growing well.

How long does kohlrabi take to grow?

It is fast, maturing in about 55 to 70 days from sowing. That quick turnaround is part of why it suits the subtropics, since it finishes before the heaviest heat and pest pressure. Pick promptly once bulbs reach size.

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