Brassicas
Kohlrabi
Brassica oleracea var. gongylodes
Timings for your region
Suggested: Moderate · Explained in the glossary
Start indoorsmid February – late June
Sow outdoorsearly April – early July
Plantingearly April – late July
Harvestmid May – early November
Practical tip
Plant shallow — set too deep it never forms a bulb. Harvest on time; left too long it goes woody.
Origin & history
Kohlrabi is a young vegetable: descriptions of a cabbage with a swollen stem only appear in European herbals in the 16th century. It became so much at home in German-speaking gardens that English, Russian and Japanese simply borrowed the German word. The “bulb” is botanically not a root but a thickened stem above ground, which is why it sits visibly on the soil.
Varieties
White — really pale green — varieties grow faster and are the choice for the first sowings; blue ones are a little slower, stand longer without splitting and suit the autumn better. For the very earliest sowing it is worth looking for varieties explicitly described as bolt-resistant, because a cold spell after planting otherwise triggers flowering. Giant varieties such as “Superschmelz” grow to head size and still stay tender — with those, size is for once not a problem.
Care
The whole job is even watering: kohlrabi grows in spurts, and when heavy rain follows a dry week the bulb splits open. It is a moderate feeder — compost at planting is enough; too much nitrogen gives lush leaves and a small bulb. With a direct sowing, thin to 25 cm in good time, otherwise the plants push each other upward and stay flat.
What can go wrong
Split bulbs are almost always a water problem rather than a fault of the variety; a mulch layer keeps soil moisture steadier than watering ever can. Early sowings bolt when the young plants meet several cold weeks after planting out — better to plant a week or two later and lay fleece over them at first. The cabbage root fly lays its eggs at the root collar; insect netting from planting day or a cardboard collar round the stem deals with that, and cabbage should only return to the same bed every four years anyway.
Harvest, storage & kitchen
Harvest at about 7 to 10 cm across, roughly tennis-ball size. Twist the leaves off at the bed — they draw water out of the bulb in the fridge; the young heart leaves are good eating and belong in the soup rather than on the compost. Without its leaves kohlrabi keeps one to two weeks in the salad drawer, autumn varieties much longer in damp sand in a cool cellar.
All timings are guide values for the given climate, not a guarantee. Weather, aspect and variety all have a say.