Loose-Leaf Lettuce

Loose-leaf lettuce is a cool-season vegetable grown for its leaves, which are used in salads and sandwiches. It is a fast-growing, long-lasting type that needs only to be planted and harvested. Plants usually reach 6 to 12 inches (15 to 30 cm) tall and wide, and the leaves can be used raw or cooked. Named leaf-type choices include ‘Red Sails’, ‘New Red Fire’, ‘Lolla Rosa’ and ‘Green Ice’.

Looseleaf types are also grown as ornamentals, and frilly or red-leaved kinds work well in flower beds and containers.

Sow seeds outdoors about 2 to 3 weeks before the last spring frost. Some guidance says two weeks before the last frost instead. If you want transplants, start seeds indoors six to eight weeks before the last frost.

Sow the seed about ¼ inch (6 mm) deep. Seeds can also be sprinkled on top of the soil or mixed into the top 1 inch (2.5 cm) layer. The optimum soil temperature for germination is 60 to 80 °F (16 to 27 °C). Seedlings usually emerge in 7 to 10 days.

Thin plants to 4 to 8 inches (10 to 20 cm) apart, depending on the variety. Sow more seed about every two weeks to extend the harvest. Plants grow in full sun to partial shade, and in summer they need about 3 to 4 hours of sun a day with shade for the rest of the day.

Keep the soil evenly moist, because lettuce has shallow roots. Water regularly, supplying about 1 to 2 inches (2.5 to 5 cm) per week. Water frequently to keep moisture steady while the plants grow.

Weeds are a problem for lettuce, so keep the bed weeded and cultivate shallowly. Mulch helps keep soil moisture even and limits weeds.

Heat and dry soil can make plants bolt, or flower, and turn the leaves bitter. High temperatures of 70 to 80 °F (21 to 27 °C) can trigger bolting. Choose heat-tolerant or slow-bolting varieties if you garden in warm weather.

Aphids, armyworms, cabbage worms and loopers feed on lettuce. Slugs and snails may also feed on the foliage. Bacterial leaf spot is worse when temperatures are cool, at 50 to 75 °F (10 to 24 °C), and when moisture is high.

Leaves can be picked one at a time, starting with the outer leaves, or the whole plant can be cut at or just above the soil. Leaf lettuce can be used once plants are 5 to 6 inches (13 to 15 cm) tall.

For cut-and-come-again harvests, cut plants just above ground level when they are 6 to 10 inches (15 to 25 cm) tall. They regrow and can be cut again 2 to 3 weeks later. Sources differ on timing: leaf lettuce is ready 50 to 60 days after seeding, while another guide says about 75 days after planting.

Leaf lettuce stores for up to four weeks if the leaves are dry when bagged. Harvest when the leaves are dry, remove the outer leaves without washing, and keep them in a mesh or plastic bag in the crisper drawer.

Lettuce sap can irritate the skin of some people who handle the plant, and the source rates this as low severity. Wear gloves if you have sensitive skin.