When to sow lettuce

Lettuce is a cool-season crop with a long sowing window. Sow outdoors from late March, once the soil has dried out enough to work, until the end of July; in the UK and milder parts of Central Europe you can carry on into early August for autumn heads. For the very first lettuces, start seeds indoors in February and plant them out from March under fleece or a cloche.

Don't sow a whole row at once. A dozen plants every two to three weeks gives you a steady supply instead of twenty heads that all bolt in the same week.

Midsummer is the tricky part. Lettuce seed germinates best at 59–68°F and increasingly fails above 68°F, so July sowings often come up patchy. Sow in the evening, water the drill with cold water first, and give the row some shade until the seedlings are up.

Hardy winter lettuces are sown in late August or September to overwinter as small plants and head up in spring. They do best with a cloche or cold frame over them.

Lettuce seed needs light to germinate, so barely cover it: about 0.2–0.4 in of fine soil or seed compost, then water gently with a fine rose or a spray bottle so the seed isn't washed away. Seedlings usually show within a week.

Sow thinly in rows 12 in apart and thin in stages. Hearting lettuces (butterhead, cos, crisphead) end up 10–12 in apart each way; loose-leaf types can stay at about 6 in. The thinnings make a good first salad.

Seedlings raised in trays or small pots are ready to plant out once they have a few true leaves. Set them no deeper than they grew: a lettuce planted too deep rots at the neck. Harden them off for a week before they go out.

A 120 × 80 cm raised bed holds three rows of four hearting lettuces, 12 heads. Grown as loose-leaf or cut-and-come-again, the same bed takes roughly twice that.

Lettuce is a light feeder. Soil that grew a well-manured crop last year, or a little compost worked in, is plenty; extra fertiliser mostly gives soft, sappy leaves that slugs love.

What it does need is steady moisture. Keep the soil evenly damp and water at the base in the morning rather than over the leaves in the evening, which keeps downy mildew and grey mould at bay.

In spring give lettuce your sunniest spot. From June a place with light shade in the hottest part of the day, for example beside taller beans or sweetcorn, keeps it growing instead of running to seed.

Bolting (the plant shooting up a flower stalk) is lettuce's response to stress: heat, drought, long days and crowding all trigger it. Once the stalk starts to rise, the leaves turn bitter within days. Keep plants watered and properly spaced, choose varieties sold as slow to bolt for summer sowings, and pick heads as soon as they are firm.

Loose-leaf lettuce is ready to pick four to six weeks after sowing. Take a few outer leaves from each plant and leave the heart to keep growing, and one sowing crops for weeks.

Hearting lettuces take about 10 to 14 weeks from sowing, less in high summer and more in spring and autumn. Press the top gently: when it feels firm, cut the head just above the soil with a sharp knife. Don't leave ripe heads standing; in warm weather they bolt within days.

Lettuce is best eaten the day it is cut. Harvest in the cool of the morning, and keep heads in a bag in the fridge for a few days at most.

Butterhead lettuces form soft, loose hearts and are the quickest of the hearting types; they are the classic spring and autumn lettuce. Cos or romaine grows tall and upright with crisp, sweet leaves and copes with summer heat a little better. Crispheads (iceberg and Batavia types) make dense, crunchy heads and take longest.

Loose-leaf lettuces such as oakleaf and lollo don't form a heart. They are the easiest to grow, the fastest to crop and the best choice for picking leaf by leaf, in pots as well as beds.

Slugs and snails are lettuce's worst enemy, above all on young plants. Check at dusk after rain, keep the bed edges clear of long grass, and plant out sturdy seedlings rather than tiny ones.

Downy mildew shows as yellow patches on the upper side of the leaves with whitish fuzz underneath. It spreads in damp weather from early summer to autumn. Space plants well, water at the base, remove infected leaves and choose resistant varieties, though new strains of the fungus keep overcoming the resistance.

Aphids gather on leaves and in the heart; a firm spray of water or their natural predators usually keep them down. Lettuce root aphid is harder to spot: plants wilt in the midday sun for no obvious reason, and the roots are covered in white, waxy powder. It spends the winter on poplars, so beds near poplar trees are more at risk; resistant varieties exist.

Lettuce belongs to the daisy family with endive, chicory and radicchio. Leave three to four years before any of them grows in the same bed again.

Because it grows fast and stays small, lettuce is the classic gap-filler: between slow crops such as cabbages or leeks, or in the space where a later crop will spread. That is practical rather than magic, and it works.

Planting tables also pair lettuce with radishes, carrots or onions, and claim that it keeps flea beetles off radishes. We found no solid evidence for these pairings; treat them as tradition. The one rule with a real reason is rotation: don't follow lettuce with other daisy-family salads.