Kohl rabi is a member of the Brassica family, it produces a fattened stem that is often used in Japanese cooking.
Sow thinly outdoors from Feburary to August in rows 1cm deep and 30cm apart. Thin out or transplant when the plants have their first true leaves so that they are 15cm apart. Water well after planting and in dry weather. Cover with fleece or netting to protect from pigeons, fleece will also stop cabbage root fly damage.
Simply loosen the soil beneath and pull up be the stem.