Seeds are generally sown between February and June. Sow two seeds per cell of cell trays in a greenhouse or similar environment until April and outdoors from April. Thin to one plant as soon as the seedlings can be handled. Give liquid fertiliser every week. When rootball is well bound together plant out into fertile garden soil in full sun or very light shade.
Allow 30cm (12in) between plants and 45cm (18in) between rows. Closer spacing will reduce the number of side shoots formed.
Before planting add 150g per square metre of general purpose fertiliser such as Growmore, or, if manure or other rotted organic matter has been dug in use half amount of fertiliser. From April, seeds can be sown in the open where the plants are to grow; sow three seeds, 2cm (¾in) deep, every 30cm (12in) along the row. When seedlings are large enough to be handled, thin out each ‘station’ leaving one healthy seedling behind.
Cover seedlings and seed beds with fleece to exclude cabbage root fly, removing fleece in May when risk of damage lessens.
Water every 10-14 days in dry periods. Add high nitrogen fertiliser, such as sulphate of ammonia, at 35g (1oz) per square metre/yard when plants about 20cm (8in) tall. Better heads are produced in cooler summers as hot weather can encourage plants to run to seed prematurely – some cultivars resist this tendency better than others.
Birds: Birds, especially pigeons, can cause an array of problems including eating seedlings, buds, leaves, fruit and vegetables.
Remedy: Protect the plants from birds by covering them with netting or fleece. Scarecrows and bird-scaring mechanisms work for a while, but the most reliable method of protection is to cover plants with horticultural fleece or mesh.
More info on Birds
Caterpillars: A number of caterpillars will feed on brassicas, but the most common are those of cabbage white butterflies. You will usually see the caterpillars, if not, you will see the holes they make in the leaves. They will also bore into the heart of cabbages.
Remedy: In mild attacks, or if you have only a few plants, you may be able to pick the caterpillars off. Insect-proof mesh or fine netting (5-7mm mesh) can prevent egg-laying.
More info on Caterpillars
Club root: Roots become swollen and distorted, and leaves become pale and yellow and wilt easily. Plants may die.
Remedy: Improve drainage and add lime to make soil more alkaline. Do not grow in affected soil.
More info on Club root
Cut when the flower shoots (spears) are well formed but before the individual flowers begin to open. Cut the central spear first. This is followed by a series of sideshoots, which can be picked regularly over four to six weeks.
Tenderstem:Not a heading cultivar, matures five weeks after planting. Each plant carries small crops of young spears that taste like asparagus.
Kabuki AGM:Compact plants suited to small garden, especially good for autumn cropping.
Fiesta AGM:Very reliable large tight heads followed by side-shoots, high yielding variety for all periods.