This alien-looking plant produces strange, bulbous, turnip-shaped globes which stand out above the soil surface, producing cabbage-like leaves.
While it looks like a root vegetable, it's actually a brassica producing green, white or purple globes which are swollen stems and tastes like a mild, sweet turnip when cooked.
It will grow in most soils but add extra lime if necessary.
Sow seeds under cover in early spring, or you can wait until the weather warms up and plant sow in beds outdoors.
Many green and white varieties are harvested in summer, while some purple types should be sown later, in July or August, for harvesting in autumn and winter.
The temperature needs to be above 10C (50F) for outdoor sowing or they may bolt. Seeds should be sown 30cm (12in) apart in groups of three. The two weakest seedlings should be removed as soon as possible, then weed and water regularly throughout the growing season.
Fast growing early varieties will be ready six weeks after sowing, while slower-growing types may take four months to mature and can be left in the ground in mild weather, although you have to lift them when there is risk of frost.
To harvest, slice them off at the root and cut off all except the youngest leaves. They should be between the size of a golf ball and a tennis ball. Don't let them mature too much or they will go woody.
Good varieties include Grand Duke', Purple Vienna' and Superschmelz'.
