Contrary to what summer salads may suggest, lettuce is in fact a cool-season crop that does best in spring, late summer, and autumn. High heat causes lettuce to bolt and run to seed. To slow summer lettuce from bolting, plant bolt-resistant varieties in light shade in mid-summer. In all other seasons, lettuce should be planted in full sun.
Thermal dormancy can be an issue where lettuce does not germinate in soil temperatures above 15°C. If planting in the very hot months (Nov-Feb), then chill seed in the fridge for a few days to break dormancy. Lettuce also needs to be shallowly sown as it requires light to germinate. All of these points can make it difficult for the novice to sow successfully every time.
Lettuce will germinate in temperatures as low as 5°C, so don’t be scared to sow directly outside early in the season. If in doubt about keeping direct-sown seed moist, cover with a thin hessian cloth for the first 5 days.
Lettuce enjoys high levels of soil fertility. Although best started off in seedling trays, lettuce can be direct-seeded and thinned in the beds.
Lettuce, Vegetable Seeds