Sow the seed about the middle March, to ensure a succession of plants, make a second sowing two weeks later.
It will be the end of May or early June before the plants are ready to be replanted into their final position. They can be planted in rows 2 ft. (60cm) apart and allow 1½ ft. (45cm) between the plants. If you want very early cabbages that are well hearted in June, sow the seed of a variety such as Primo early in February a cold frame in rows 6 in. (15cm) apart. When the plants come through, they must be given some ventilation on warm days. Increase the ventilation in March or early April so that they harden off ready to be planted into their permanent position. Allow 1½ ft (45cm) between rows and 1 ft. (30cm) between plants.
Keep down the weeds; watch out for pests such as greenfly, whitefly, and caterpillars. A good way to protect the crop is to add a barrier of fine netting or fleece to keep the flying insects off the plants.
The cabbages can be cut as soon as they have good hearts. Pull up stumps, put them on the compost heap.