All The Year Round
Lettuce (Butterhead) in the UK

You can start these off indoors in trays from March, or sow direct into the soil once the ground warms up a bit, usually from April. Just sprinkle the seeds thinly over a shallow drill, about a centimetre deep, and cover them lightly. Keep the soil damp, and they'll usually pop up in about a week. To keep a steady supply coming, sow a small batch every two to three weeks right through to August. That way, you'll always have some fresh heads ready to pick.

If you've started them indoors, prick out the seedlings gently once they've got their first proper leaves, giving them some space in individual pots or modules. Harden them off outside for a week or so before planting them out after the last risk of frost, which up here in the North is usually mid to late May. Give them about 25 cm between each plant, so they've got room to develop. They do well in containers too, especially the smaller varieties.