Plant out in well-drained, fertile soil with plenty of organic matter, keeping the soil consistently moist, but not waterlogged, to prevent bolting and bitterness. Protect young plants from frost with cloches or fleece, and thin them to around 20-25cm (8-10in) apart for good airflow.
Harvest outer leaves as needed for a continuous supply, or cut the whole head when mature; for spring crops, harvesting in the cooler mornings keeps leaves crisp and sweet. Rotate with other crops to reduce disease risk and watch for slugs in damp conditions.