Brassica oleracea, Acephala Group. (Cruciferae). A biennial, closely related to the cabbage, grown as an annual for its edible shoots and young leaves. The species probably originated in Western Europe along the coast of the Mediterranean and is now widely distributed in both temperate and tropical regions. It is one of the hardiest brassicas, capable of withstanding winter temperatures as low as –15ºC, and also tolerant of high summer temperatures. The main season of availability is through the winter until spring, when the kale breaks into new growth at a time other vegetables are in short supply. Shoots and leaves are cooked in a similar manner to cabbage.

Although kale will tolerate poorer soils than other brassicas, it does best in a nutrient-rich, well-cultivated soil, well manured during the previous autumn. A topdressing of a nitrogen fertiliser in the spring will encourage new shoot growth, and is particularly beneficial when heavy leaching has been brought about by winter rainfall.

Transplants may be raised from sowing during the spring and should be large enough within 6-8 weeks. Plant firmly and water in during the summer. Spacing will depend on the cultivars used but 45cm between plants is sufficient for the dwarfer types and up to 75cm for the taller ones. When the tops of the plants are harvested the lower leaves should be allowed to remain to encourage the growth of side shoots for later harvests. With rising spring temperatures flowering will begin and the site should be cleared for other crops.

Kale can also be grown at a closer spacing for an early crop of spring greens. Seeds should be broadcast under cloches during the latter part of the winter or in the open during early spring and thinned to 7-10cm between plants. These can be harvested as spring greens when no more than 15cm high, and the remaining stems allowed to resprout for a further harvest.

The wide range of available forms may be broadly classified into the curly or Scotch kales (borecole) and the broader smooth-leaved types. Rape or Siberian kales are similar in appearance to the curly kales but are a different species (Brassica napus). These ‘rape kales’ will not withstand transplanting and must be sown in situ. A number of kales grow extremely tall, including the so-called Jersey kale, also known as tree cabbage, walking-stick cabbage, Jersey longjacks and chou cavalier. Though normally reaching around 150cm, it has been recorded to 540cm. The straight, relatively slender stems are strong enough to dry and make into walking sticks; the 75cm leaves are decorative and can be cooked when young.

Recommended cultivars include ‘Dwarf Green Curled’, ‘Konserra’ (winter-hardy), ‘Tall Green Scotch Curled’ and ‘Vates’ (‘Dwarf Blue Curled Scotch’), short and wide-spreading. The F1 hybrid ‘Fribor’ has finely curled, deep green leaves. The plain-leaved types include ‘Cottager’s’, ‘Hardy Sprouting’, ‘Russian Red’ (leaves wavy, with red-purple veins) and ‘Thousandhead’.

Pests and diseases are similar to those of other brassicas although kale is less densely affected by club root than others of the group.