January King, although a French heirloom, is also considered to be a traditional British cabbage and one of the best varieties for winter use. They are well adapted, withstanding frost and winter rain and remain crisp and crunchy with excellent colour.
One of the hardiest Cabbages, which from November to January produce heads that have a good sweet flavour and crisp crunchy texture.
It is a distinct type of cabbage with the characteristic conifer-blue leaf colour, the outer leaves of the heart have a red tinge and the leaves have light blistering like a Savoy.

Prepare the site:
All brassica crops grow best in partial-shade, in firm, fertile, free-draining soil. Start digging over your soil as soon as you can brave the elements. Remove any stones you find and work in plenty of well-rotted manure or compost. Tread on the soil to remove air pockets and to make the surface firm. Brassicas will fail if the soil is too acidic; add lime to the soil if necessary, aiming for a pH of 6.5-7.5.

Sowing: Sow successionally from February to July
Nearly all brassicas should be planted in a seedbed or in modules under glass and then transferred. Seeds should be sown thinly, as this reduces the amount of future thinning necessary and potential risk from pests.

Sow seeds 1.25cm (½in) deep and space 15 to 20cm (6 to 8in) between rows.
Once the seeds have germinated, thin the seedlings to 7.5cm (3in) between each plant. After germination, seedlings will often be ‘leggy’, so plant them as deep as possible to really anchor them into the soil.

Cabbage seedlings are ready for transplanting when they are between 6 and 8cm high (2½ -3"). Water the day before moving, and keep well-watered until established. Plant firmly, close together for small heads and wider apart for larger cabbages, around 30 to 45cm (12 to 18in) apart.

Growing:
Clear away any yellow leaves. Feed the plants as they near maturity with a foliar feed.

Harvest:
June to August (through to October)
Earliest heads can be cut, leaving the stump in the ground to produce a second crop of small leafy heads.

Tips:
Brassicas are affected by a wide range of pests and diseases, especially the fungal disease, club root. The roots become stubby and swollen and can develop wet rot, while leaves become yellow and wilt, causing severe stunting of growth. Remove any infected plants from the ground and destroy. Make sure the soil is adequately limed and well drained.

Rotate your crops annually to avoid disease. Don't grow brassicas on the same plot more often than one year in three, as moving the crop helps avoid the build up of soil pests and diseases

Companion Plants:
Mint: Effective against Cabbage White Butterflies, Aphids / Flea Beetles
Thyme: To ward off that nasty Cabbage Worm!
Also useful: Sage, Oregano, Borage, chamomile and Nasturtium.