Ready to stretch your growing season: get an early start in spring or keep the season going in autumn? Lettuce is your choice.
Lettuce does not like warm days and nights, so the cool time of the year is lettuce season. You can lengthen your growing season dramatically with a lettuce box–that’s a cold frame dedicated to lettuce growing. A lettuce box will protect the earliest and latest plantings, and with a light shade cloth cover, use the lettuce box for summer harvests as well.
If frost is not in the forcast over the next 40 to 60 days tuck lettuce into flower-borders. Otherwise in early spring and autumn, use the lettuce box or be ready to give lettuce some overnight protection when frost comes. Lettuce leaves stung by frost can be clipped away and you can keep on growing new leaves from the center.
Planting Calendar. Lettuce is a cool-weather crop that requires 40 to 50 days to reach harvest. Lettuce will send up a stalk and bolt or go to seed in temperatures greater than 80ºF (27ºC). Bolted lettuce is inedible.
Spring crops. Sow lettuce seed directly in garden 4 to 6 weeks before the average last frost date in spring. If your growing season is short or hot weather arrives quickly, sow seed indoors in late winter 10 weeks before the average last frost date and transplant seedlings to the garden early so that they mature before the weather gets hot. Small seedlings can be protected by cloches until after the last frost.
Autumn and winter crops. Sow lettuce in late summer for harvest from autumn to early winter. Protect last autumn and winter crops with cloches or plastic tunnels if necessary. Some varieties will over-winter under cloches or in cold frames. In mild winter regions, sow lettuce in autumn for harvest in winter.
Succession growing. Sow lettuce every 2 weeks until early summer to ensure an ongoing supply.
Place. Lettuce grows best in full sun but prefers light shade in regions with hot summers.
Soil. Lettuce prefers rich, loose, well-drained soil that does not dry out. Add plenty of garden compost to planting beds before sowing. Add a handful of blood, fish, and bone meal to each square yard/meter before sowing. Lettuce prefers a soil pH of about 6.5.
Space. Sow lettuce seed ½ inch deep. Thin leaf lettuce seedlings from 6 to 8 inches apart when they are large enough to handle. Thin head lettuce seedlings to 12 inches apart. Space rows from 10 to 16 inches apart. Lettuce that is crowded may bolt. Thinned seedlings can be transplanted to another part of the garden or used in salads.
Container growing. Lettuce grows well in containers and can be grown indoors in winter. A single head lettuce can be grown in a 6-inch pot. Space lettuce 10 inches apart in larger containers. Lettuce grown in containers should be moved to a cool place when the weather warms.
Water. Lettuce prefers moist but not wet soil. Lettuce is shallow rooted; the soil should not be allowed to dry out. Keep head lettuce well watered when the heads are forming. Use a light mulch of straw or hay around lettuce to keep the soil moist and to keep muddy water from splashing onto leaves.
Feed. Add plenty of garden compost to lettuce planting beds before sowing seeds. Side dress lettuce every 2 weeks with compost tea during the growing season. Add additional garden compost to the garden before planting a second or third crop during the growing season.
Selected varieties. There are three basic types of lettuce: head lettuce, loose leaf lettuce, and stem lettuce. Head lettuce forms a tight head and is also called iceberg or crisphead lettuce. Loose leaf lettuce has a head of loose, open leaves. Stem lettuce forms thick stems and smaller leaves. Head lettuce varieties include Great Lakes (90 days); buttehead varieties include Summer Bibb (62 days) and Buttercrunch (75 days). Leaf lettuce varieties include Black-seeded Simpson (45 days); Ruby (45 days); Red Sails (45 days). A cos lettuce or romaine lettuce variety is Parris Island Cos (73 days). Stem lettuce varieties include Celtuce (80 days).