Lactuca sativa

Lettuce is an erect, edible, annual, cool season vegetable plant in the daisy family (Asteraceae). It is native from the Mediterranean to Siberia and has been bred to grow in an array of shapes, colors, and textures for a variety of growth conditions, storage purposes and interest on a plate. The general categories of lettuce types include head lettuce, romaine, leaf lettuce and butterhead (loose head).

Lettuce grows best in full sun to partial shade and organically rich, moist, well-drained soils. Optimal pH ranges from 6 to 6.7. Lettuce enjoys the cool weather of spring and fall. If grown during summer, give the plant 3 to 4 hours of sun daily and shade the rest of the day. Lettuce has a shallow root system and requires consistently moist soil for proper growth and flavor. Both high temperatures (70 to 80 degrees F) and dry soil can trigger plants to bolt and flower, turning the leaves bitter and stopping leaf production. Consider planting heat-tolerant varieties, if growing lettuce in warm climates. Leaf and butterhead types tolerate heat better than romaine, which itself does better in heat than head lettuce. Propagate lettuce by seed.

For a spring crop, seeds can either be started indoors six to eight weeks before the last frost for later transplanting or directly seeded two weeks before the last frost. For a fall crop, sow seeds three months before the first frost. Plant seeds to a depth of 1⁄4 to 3⁄8 inch. Different lettuce types need different spacing; head lettuce generally needs 10 inches between plants and leaf lettuce 4 to 6 inches. Alternatively, leaf lettuce seed can be sprinkled on top of the soil or mixed into the top 1 inch layer. Lettuce can also be grown in containers that are a minimum of 2 quarts volume and 6 to 8 inches deep. Plant additional seed at two week intervals to extend the harvest. 

Leaves can be harvested either by removing individual baby leaves (2 to 3 inches long) for a continuous harvest or by cutting the whole plant at or above the soil surface. Lettuce rapidly grows to 6 to 12 inches tall and wide. If removing leaf by leaf, take the outer leaves first to allow the central leaves to continue to grow. Head lettuce is ready to harvest 70 to 80 days after seeding or 60 to 70 days after transplanting while leaf lettuce is ready 50 to 60 days after seeding and 30 to 45 days after transplanting.

Insects, Diseases and Other Plant Problems: Lettuce is attacked by aphids, armyworms, imported cabbage worms and loopers. The pest pressure on summer and fall crops is much greater than on spring crops. Damping-off is a serious disease of young seedlings, whereas mildews and sclerotinia are serious on mature plants.

More information on growing, purchasing and cooking lettuce

VIDEO Created by Elisabeth Meyer for "Vegetables, Herbs, Fruits, and Nuts" a plant identification course offered in partnership with Longwood Gardens.