Kohlrabi (Brassica oleracea gongylodes) is rarely sold in UK supermarkets but is well worth trying. The light green or purple ball-shaped roots have a crisp texture and delicate flavour, somewhere between a turnip and a cabbage. The name is actually taken from the German Khol (cabbage) and Rabi (turnip).
Soil Type: Moderately fertile, moist but well drained, light soil.
Conditions: Open sunny position.
Ease of Cultivation: Easy.
Type: Brassica Leafy Vegetable.
Hardiness: Hardy in most regions of the UK.
When to Sow: February to May.
Harvest Season: July to September.
Kohlrabi is easier to grow than turnips in hot and dry weather.
Follow standard crop rotation rules for brassicas. Do not grow in ground that has been used for brassicas in the last few years.
Plant in a moist but well-drained, rich soil, in full sun. The ground should be deeply dug and moderately enriched several months before planting. Apply garden lime if the soil is acidic. Soil pH should be around 7.
Sow under cover from February to March. Plant out when about 2in (5cm) high in a greenhouse or under a cloche. Spacing around 6-8in (15-20cm) between plants.
Direct sow from late April onwards in rows 12in (30cm) apart, thinning to 6-8in (15-20cm) between plants.
Sow every few weeks for a regular supply. Hardy varieties can also be sown under cover in early autumn for winter use.
Keep the site weed free and water well in dry weather.
As part of the brassica family Kohlrabi is vulnerable to the same diseases, such as club-root and cabbage root fly. As a relatively quick crop it is usually trouble free.
Slugs can attack young seedlings, so use a slug control when the plants are small.
Harvest from late July to December, once the globes are about 6-4in (10-15cm) across. Use straight away as they won't store for long.
If left in the ground too long they can become woody and tough, so the crops are best pulled and eaten when young and tender.
Trim the leaves off and scrub clean. Small globes can be cooked whole. Larger Kohlrabi should be peeled and sliced or diced. Boil in slightly salted water for 30-60 minutes, depending on size.
Serve with melted butter. They can also be mashed with butter or sour cream.
Kohlrabi provide a rich source of vitamins A, C and K and folate, as well as beta carotene and lutein.
Available in light-green or purple forms. Purple skinned varieties are usually hardier and can be left to grow a little larger without becoming tough.
Kohlrabi 'Kolibri' (F1 Hybrid) is a purple-skinned variety with white, succulent flesh. Best harvested when small, although they can be left to grow larger. Very quick to mature, at around 8 weeks from sowing. Thompson & Morgan.
Kohlrabi 'Kongo' (F1 hybrid) is a fast-growing, high-yielding variety with very pale green squat bulbs. The tasty flesh is sweet moist, and tender flesh. Best harvested when young.
Kohlrabi 'Kossak' (F1 Hybrid) easy to grow, bolt resistant and fast maturing. Can be harvested in as little as 12 weeks from sowing. Produces large pale green globes of up to 3kg that remain tender without becoming woody. Thompson & Morgan.
Kohlrabi Korist (F1 hybrid) is a fast growing early maturing variety suitable for growing under glass. The flattened globe shape bulbs are tender crisp, and juicy.
Kohlrabi 'Purple Danube' produces attractive purple-pink globes with sweet tasting white flesh.
Kohlrabi 'Purple Vienna' purple-skinned variety that is ideal for late sowing.
Kohlrabi 'Quickstar' (F1 hybrid) is a high-yielding crop that matures quickly. Slow to bolt.
Kohlrabi 'Rapidstar' (F1 hybrid) produces uniform, medium to large, smooth, greenish white bulbs that mature early. Slow to bolt.
Kohlrabi 'White Danube' pale green variety with clean white flesh.
Kohlrabi 'White Vienna' a good pale green-skinned variety.