Lettuce

Lettuce is a cool-season crop propagated from seed, either sown directly or started indoors for later transplanting, with spring crops begun several weeks before the last frost and fall crops begun a few months before the first frost. Seed is sown shallow, roughly 1/8 to 3/8 inch deep, and germinates in about one to two weeks; spacing depends on type, with head lettuce thinned to 10-12 inches and looseleaf types left at 4-8 inches, or seed scattered thickly for a cut-and-come-again bed. Sowing small batches every two to three weeks keeps a continuous supply coming without a glut.

Lettuce grows best in full sun during cool weather but appreciates partial or afternoon shade once temperatures rise, and it adapts well to containers at least 6 to 8 inches deep. Its shallow roots need organically rich, well-drained soil kept consistently moist, and watering in the morning lets foliage dry by evening; growth is best around 60 to 65°F.

Lettuce is attacked by aphids, armyworms, imported cabbageworms and loopers, with pest pressure heavier on summer and fall crops than on spring ones. Slugs and snails commonly shelter beneath the leaves and chew them, and seedlings can also be damaged by birds such as blackbirds and sparrows.

Damping-off is a serious threat to young seedlings, while mildews, powdery mildew, botrytis, sclerotinia and lettuce mosaic virus affect more mature plants; keeping foliage dry helps limit fungal problems. High temperatures above roughly 70 to 80°F or dry soil push plants to bolt, and as they do, rising latex production turns the leaves bitter.

Leaves can be picked individually as baby leaves 2 to 3 inches long, taking the outer leaves first so the center keeps producing, or whole plants can be cut at or just above the soil line. Head lettuce is generally ready 70 to 80 days after seeding or 60 to 70 days after transplanting, while leaf lettuce matures faster, in 50 to 60 days from seed or 30 to 45 days after transplanting; hearting types should be cut as soon as they mature and before they bolt.

Storage: harvested lettuce keeps in a plastic bag in the refrigerator for up to about six days.

Culinary: Lettuce leaves are eaten mostly raw in green salads but also appear in sandwiches, wraps and soups, and can even be grilled; romaine is the traditional base of Caesar salad. Celtuce, grown for its thick stem rather than its leaves, is eaten raw or cooked and is popular in China and Taiwan.

Medicinal: In 17th-century England, the herbalist Gerard recorded lettuce as a means of increasing milk production in nursing mothers, a use tied to the era's doctrine of signatures rather than any demonstrated effect.

Lettuce was first cultivated by the ancient Egyptians, who turned a plant originally grown for its oil-rich seeds into a crop raised for its succulent leaves, and it appears in Egyptian tomb paintings dating back to around 3000 BC. It probably originated in the southern Mediterranean region before spreading to the Greeks and then the Romans, who named it lactuca for its milky sap; by 50 AD many types were already described. European cultivars developed between the 16th and 18th centuries persist in gardens today, and lettuce reached the New World when Columbus carried it there in 1493, with the Pilgrims later bringing its seeds to Plymouth.