Lettuce

Lettuce varieties can be loosely categorized into four groups: crisphead, butterhead, leaf, and romaine or cos. Each group has its own growth and taste characteristics:

Crisphead lettuce, probably the most familiar of the four, is characterized by a  tight, firm head of crisp, light-green leaves. It is generally intolerant of hot weather and will readily bolt or send up a flower stalk under hot summer conditions. Its long growing period also makes it one of the most difficult of the lettuces to grow in New England .

The butterhead types have smaller, softer heads of loosely folded leaves. The outer leaves may be green or brownish with cream or butter colored inner leaves.

Leaf lettuce has an open growth and does not form a head. Leaf form and color varies considerably – some cultivars are frilled and crinkled and others deeply lobed. Color ranges from light green to red and bronze. Leaf lettuce matures quickly and is the easiest to grow.

Romaine or cos lettuces form upright, cylindrical heads of tightly folded leaves. The plants may reach up to 10 inches in height. The outer leaves are medium green with greenish white inner leaves. Romaine is the sweetest of the four types.

Climate Requirements

Lettuce is a cool-season vegetable and develops best quality when grown under cool, moist conditions. Lettuce seedlings will tolerate a light frost. Temperatures of 45–65oF are ideal. Seeds of leaf lettuce are usually planted in the spring as soon as the ground can be worked. Butterhead and romaine can be grown either from seeds or transplants. Due to its long-growing season, crisphead lettuce is grown from transplants. Transplants may be purchased or started indoors about six weeks before the preferred planting date.

Soil Requirements

Lettuce can be grown in a wide range of soils. Loose, fertile, sandy loam soils, well-supplied with organic matter, are best. The soil should be well-drained and moist but not soggy. Heavy soils can be modified with well-rotted manure or compost or by growing a  cover crop. Like most other garden vegetables, lettuce prefers a slightly acidic soil with pH 6.0 to 6.5.

Cultural Practices

Since lettuce seed is very small, a well-prepared seedbed is essential. Large clods will not allow proper seed-to-soil contact, thereby reducing germination. Lettuce does not have an extensive root system, making an adequate supply of moisture and nutrients also necessary for proper development.Fertilizer and lime recommendations should be based on the results of a soil test. As a general rule, however, apply three to four pounds of 5-10-10 fertilizer per 100 square feet of garden area.

Seed may be sown in single rows or broadcast for wide row planting. Wide rows should be 12–15 inches across. Cover the seeds with ¼- to ½-inch of soil. Water carefully but thoroughly. Several successive plantings of  leaf lettuce will provide a more continuous harvest throughout the growing season. Leave 18 inches between the rows for leaf lettuce and 24 inches for the other types. To achieve proper spacing of plants, thinning of lettuce seedlings is usually necessary. Thin plants of leaf lettuce 4–6 inches or more between plants, depending on plant size. Butterhead and romaine should be thinned 6–10 inches between plants. Crisphead transplants should be spaced 10–12 inches apart in the row.

An organic mulch will help conserve moisture, suppress weeds, and keep soil temperatures cool. If weeds become a problem pull them by hand or cultivate very shallowly to avoid damage to lettuce roots. Planning your garden so that lettuce will be in the shade of taller plants in the heat of the summer may reduce bolting.

Harvesting

All lettuce types should be harvested when they have reached full size but are still young and tender. Overmature lettuce is bitter and woody. Leaf lettuce is harvested by removing individual outer leaves, leaving the center leaves to continue to grow. Butterhead or romaine types can be harvested by removing the outer leaves, digging up the whole plant, or cutting the plant about an inch above the soil surface, usually allowing for a second harvest.Crisphead lettuce is picked when the center is firm.

Adapted from Marianne Riofrio, Ohio State University Extension, 2000