Lettuce

Light and exposure

In spring and autumn, lettuce likes the sun, which gives it well-formed, crunchy heads. A sunny position is ideal for sowings from early spring to early summer, and for those of late summer.

In high summer, give it partial shade. Heat and full sun make it bolt and turn bitter. The light shade of a row of tomatoes or beans, or the side of a hedge that only catches the morning sun, clearly extends the summer harvest.

Watering

Lettuce is mostly made of water and has shallow roots, so it needs a soil that stays cool at all times. Water regularly, preferably in the morning, at the base and avoiding soaking the heart of the heads.

Water stress is the first trigger of bolting and bitterness. A soil that dries out then is rehydrated all at once also makes the heart split and rot. A light mulch keeps the moisture steady and limits soil splashing onto the lower leaves.

Soil and repotting

Lettuce likes a loose, cool soil, rich in humus and well drained. A little mature compost worked in before planting supports its quick growth. It has no great demands, but a soil that holds moisture makes all the difference.

Avoid soils that dry out on the surface or compact after rain. In heavy soil, an addition of compost lightens the structure and improves water retention without excess, because the roots rot in a waterlogged soil.

Temperature and humidity

Lettuce is a cool-season plant. It germinates and grows best between 12 and 20 degrees, and tolerates light frosts late in the season, especially the winter varieties. It is a vegetable cut out for cool temperate climates.

Its constraint is not cold but heat. Above 25 degrees the seed germinates poorly and the plant bolts. Direct sowing in open ground is possible as soon as the soil has drained at the end of winter, and continues until the end of summer. The very first sowings are done rather under cover, in a cold frame or in pots, to be transplanted once the last frosts have passed.

Pruning and upkeep

Lettuce is not pruned, but it needs thinning or transplanting at a good distance. Crowded, lettuces head up poorly and rot at the heart. Leave twenty-five to thirty centimetres between the head varieties, a little less for cutting lettuces.

For cutting varieties and oak-leaf types, harvest leaf by leaf as needed, taking the outer leaves. The heart keeps producing, and a single plant thus supplies several weeks. Remove the yellowed lower leaves along the way to air the plant and cut short the slugs.

Pests and diseases

Slugs are lettuce’s number one enemy in a damp climate. They devour young plants in a night and hide under the lower leaves. Pick them off in the evening, clear the collar of the plants, and think of barriers or traps around the sowings.

As for diseases, watch for lettuce downy mildew, caused by Bremia lactucae, which marks the top of the leaves with yellow patches and the underside with a white felting in mild, damp weather. Grey mould and collar rot lie in wait for plants that are too crowded or too watered at the heart. Air them, space them out and water at the base in the morning.

Propagation

Lettuce is sown very simply, on the surface or barely covered, because the seed needs light to germinate. Sow in pots or trays to transplant, or directly in place and thin out afterwards. Emergence takes a few days.

The key move is staggered sowing. Sow a small quantity every fortnight, from spring to the end of summer, rather than one big bed all at once. You thus spread out the harvest instead of ending up with twenty salads ready the same week. In high summer, sow in partial shade and in the cool, because the seed germinates poorly in the heat.

Month-by-month care calendar

Green Hub tips

• Sow in stages, a few plants every fortnight from spring to the end of summer. You will have salad continuously instead of twenty heads ready the same week.
• In high summer, sow in partial shade and water without fail. It is heat and lack of water that make lettuce bolt and turn bitter.
• Against slugs, clear the collar of the plants, remove the lower leaves and do an evening round. They love damp nights.
• For cutting varieties, harvest leaf by leaf taking the outside. The heart starts again and a single plant feeds you for several weeks.