Insects can be troublesome just after transplanting (but rarely later on). We always have a small bottle of Btk (Bacillus thuringiensis var. kurstaki) on hand. A bacterium that poses no threat to humans, birds, pets, fish, honeybees or spiders, Btk is mixed with water and sprayed over kale, cabbages and broccoli to control green cabbage worms, the caterpillar stage of white cabbage butterflies. Spray at the first sign of butterflies and again after heavy rains if cabbage whites are still flitting around.
Three to four weeks after transplanting, preferably just after a soaking rain, we lay down a 30-centimetre-wide circle of compost four to five centimetres thick around each plant. A deep, weekly drink and a monthly soaking with diluted fish emulsion or other liquid plant food keeps kale moving along. Routine cleanup is also a good idea: as bottom leaves droop and yellow, snap them off to send all the energy into tender new top growth.
Although you can eat a little kale in summer, light frosts tenderize and sweeten leaves, so October through December is the proper time to harvest. Very young leaves are fine for salads (see In the raw below), but to my taste, mature kale is too tough and strong to be eaten as such. Quick stir-frying results in undercooked and chewy fare—better to blanch leaves in boiling water for a minute or two before adding to stir-fries. Simmering kale slowly, however, either on its own or in a hearty soup, brings out the best in this full-bodied, wholesome vegetable.
In the raw
Kale for the salad bowl should be picked small and tender (Siberian varieties are best). Sow seeds thickly (one centimetre apart) directly in the garden in a 15-centimetre-wide band or broadcast over a square of ground. Thin seedlings over time to eight centimetres apart (you can eat the thinnings); then snip young leaves from the stalks, allowing tops to grow.