Kohlrabi is one odd-looking vegetable. Just above the ground, its stem swells into a ball-shaped knob from which spindly leaves radiate, giving it the appearance of a leafy flying saucer.
Kohlrabi, German for "cabbage turnip", is a member of the cabbage family, traditionally enjoyed in Germany and Eastern Europe but uncommon in North America. This is unfortunate, because kohlrabi is easy to grow and pleasant to eat. The bulbs have a crisp, crunchy texture when eaten raw and taste somewhat like a mild, slightly sweet cabbage.
Kohlrabi bulbs have white flesh and greenish white or reddish purple skin. They can be eaten raw in salads or as part of a vegetable dip platter, or cooked in stir-fries, soups or stews. The young leaves, which have a flavour similar to kale or collards, are good steamed or sautéd, or in soups or stews. The bulbs are a good source of vitamin C and potassium. The leaves are rich in calcium, potassium, iron and carotene and have the same anti-cancer properties as other members of the cabbage family. Most kohlrabi varieties are best harvested when bulbs are four to five centimetres in diameter. At that size, bulbs retain their mild flavour and crisp, non-fibrous texture. Some of the new hybrids, such as 'Express Forcer' and 'Kolibri', stay tender and mild up to 10 cm. Large varieties, such as 'Gigante', can be harvested up to 25 cm in diameter.
Kohlrabi (Brassica oleracea, Gongy-lodes Group) originated in the coastal areas of the Mediterranean Basin. By AD 800, the French emperor Charlemagne ordered that it be grown in his kingdom. However, it was fed only to cattle because the royal physicians warned that it would make his soldiers bovine and unaggressive.
Planting and growing
Choose a site that receives full sun, with well-drained soil rich in moisture-retaining organic matter. In early spring, loosen the soil and dig in five to eight centimetres of compost or composted manure. Although kohlrabi plants will withstand light frost, young plants may bolt without forming bulbs if exposed to temperatures below 5°C for more than a couple of days. Once the temperature is consistently over 5°C, make a trench 12 millimetres deep with a hoe. Sow seeds two centimetres apart and cover with soil so the seeds are six millimetres deep. Rows should be 30 to 45 centimetres apart. For wide beds, plant two or three seeds 15 centi-metres apart in all directions. As soon as the first true leaves develop, thin to the most vigorous seedling per spot. If you're growing a giant variety for competition, space 60 to 90 centimetres apart.
Keep the soil moist but not soggy while the seeds germinate. Use a floating row cover to protect emerging seedlings from flea beetles, which can decimate young plants, and check regularly to ensure plants aren't being attacked by aphids. Keep covered until they're 10 centimetres tall to help prevent early cabbage worm infestations. When the leaves begin to touch, thin plants to five centimetres apart. When the leaves touch once more, thin to 10 centimetres apart. Large varieties will need to be thinned again to at least 20 centimetres apart.