This strange-looking brassica resembles a Sputnik, but don’t let this put you off. It has a delicious broccoli-like flavour and is more drought resistant than most brassicas, so succeeds where swedes and turnips fail. Green varieties are sown from mid-spring to mid-summer for summer crops, while hardier purple varieties are sown from mid-summer for autumn and winter harvests.
Jobs to do now
- Sow seeds outdoors
- Thin out seedlings
- Water regularly to keep the soil moist
Month by month
Kohl rabi is easy to sow outdoors in spring and summer. It likes a sunny spot in any reasonably light, fertile, free-draining soil.
Prepare the sowing site by weeding and raking to remove lumps and stones, then make a drill 1cm (½in) deep. Water along the base, then sow seeds thinly, cover with soil and firm gently. Space rows 30cm (1ft) apart. You can sow from late February to early March under cloches or fleece, then in open ground through spring to about mid-summer, or to mid-August in warmer areas.
Sow little and often, say every three weeks, for a constant supply.
In cooler areas and where the soil is heavy clay, early sowings can be made indoors in modules. Harden off the seedlings and transplant outdoors when they are a maximum of 5cm (2in) tall, once the soil has warmed up.
Thin out seedlings when they are 2.5cm (1in) tall or the first true leaves appear, leaving a final spacing of 15cm (6in) apart.
Keep the soil constantly moist and weed free, watering before the soil dries out.
Place netting or fleece over young plants to protect against birds and cabbage root fly.
Harvest kohl rabi when young, between golf ball and tennis ball size. If you leave them too long they lose their flavour and tenderness.
With repeated sowings, plants can be harvested from May through to November, and the leaves can also be eaten.
Green varieties, sown from mid-spring, are ready in summer, while hardier purple varieties, sown in summer, provide autumn crops.
Cabbage root fly
White larvae approximately 5cm (2in) long, feed on the roots just below the soil surface, stunting growth and causing plants to wilt and die.
Grow under insect-proof mesh or horticultural fleece. Seedlings are most vulnerable.
Leaves are covered in small holes and damaged areas turn brown. Seedlings are particularly susceptible.
Grow plants under horticultural fleece and keep the soil moist. Water in nitrogen-rich fertilser to help the crop outgrow the pest.
Roots become swollen and distorted, and leaves become pale and yellow and wilt easily. Plants may die.
Improve drainage and add lime to make soil more alkaline. Do not grow in affected soil.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.