Unblanchedis bitter and virtually inedible; blanching is essential to produce tender palatable shoots. There are two ways in which blanched shoots can be produced. They can either be blanched ; in situ outdoors, or forced indoors. With either method the shoots must be given some protection from the cold while they are being blanched during the winter.
If you do not have any specialized seakale pots, perhaps the easiest method outdoors is to cover each plant with an upturned bucket, box, large flowerpot or other suitable container. Do this as soon as the foliage dies down in the autumn, clearing away all the dead foliage and lightly forking around the plants first.
Then place the containers in position, weight each one down with a brick and then surround each with a circle of wire netting staked to a short post. There should be a space of about 7.5 cm (3”) between the container and the netting. Fill this space with leafmould. The leafmould provides protection from the cold and will ensure blanched stems for harvesting in early spring. Alternatively, you can use half-rotted manure instead of leafmould. The heat produced by the decomposing manure means that the blanched stems will be produced a little earlier. If you cover part of the rows at, say, 10-day intervals from early winter onwards, you should be able to ensure a succession of blanched shoots for harvesting in the spring.
It is possible, instead of using wire netting, to cover the rows with leaf-mould or manure and then to hold this in place with planks. Cover the shoots as soon as they peep through and harvest them soon afterwards.
A better succession of crops can be obtained by forcing the seakale indoors. Lift the crowns successively in mid- to late autumn and cut the main root down to about 15 cm (6”) long, removing all the side roots. Then plant them upright 7.5 cm (3”) apart in deep boxes containing moist leafmould, pottingor peat 25 cm (9”) deep. The crowns should just appear above the surface.
Place the boxes in a dark place such as a cellar, garden shed or under the staging of a greenhouse. Cover them with lids of cardboard, wooden boxes or pots, making sure that all light is excluded. If any light reaches the stems while they are blanching, they will become bitter.
The ideal temperature at which to force seakale is 7°C (45°F) to start with, rising to 13’C (55°F) later on. At these temperatures the shoots should be ready for harvesting in about five to seven weeks; at colder temperatures they will take longer. Do not, however, try to rush the plants by forcing at temperatures above 13°C (55°F). If you do, the blanched stems will be thin and wiry.