A member of the Asteraceae, or aster, plant family, lettuce (Lactuca sativa) develops from a rosette that forms either a compact or a loose cluster of leaves joined at the base just above the soil. Leaf lettuce starts out as others do, but unlike head lettuces, its leaves separate from each other during the growing process, with plants growing to about 8 inches at maturity.
There are two basic types of leaf lettuce: green leaf and red leaf. After germination, the first leaves are small and bright green, with the red-leaf varieties developing their characteristic maroon color as the leaves mature. The leaves of both varieties grow from the base of the stalk, opening like a flower as they get larger. The leaves of "Grand Rapids," a green-leaf variety, have frilly edges, as do the leaves of a red-leaf variety called "Red Fire." The darkest red leaves are produced by "Ruby," and the bright green leaves of "Black-seeded Simpson" are the earliest to appear. Other green-leaf varieties to look for include "Oak Leaf," that does well in hot weather as it is resistant to tip burn, and red-leaf varieties "Red Sails," which is said to be the slowest bolting of the red leaf lettuces.
Unlike head lettuces that need a certain amount of time to develop into compact heads, leaf lettuce can be harvested as baby lettuce as soon as the individual leaves are about 5 to 6 inches tall. As a cut-and-come-again vegetable, cutting the first leaves from the plants encourages new growth, until they reach their maximum size of about 8 inches and weigh about 6 to 12 ounces. Because of its short growing season, leaf lettuce can be grown throughout the spring, early and late summer and early to late fall. Hardy in U.S. Department of Agriculture plant hardiness zones 4 to 9, successive plantings spaced about a week apart assure a steady supply almost all year long, with the exception of the winter months in areas where temperatures remain consistently below freezing and the mid-summer months when the heat can be a problem. Leaf lettuce is not tolerant of intense heat or drought, nor does it compete well with weeds, making it important to keep it well watered during hot weather and the area kept as free of weeds as possible.
Planting Leaf Lettuce
Leaf lettuce does best in soil that has been enriched with plenty of organic matter such as compost or aged manure, and can be started inside about 6 weeks before the last spring frost or outside as soon as the soil can be worked. Plant seeds 1/2 inch apart and thin to stand 4 inches apart. Keep seedlings or seed rows moist until plants are established. Leaf lettuce can be sown in narrow rows or broadcast across wide rows about 12 to 15 inches across. Cover seed with no more than 1/2 inch of soil, and allow 18 inches between the rows. The Ohio State University Extension recommends performing a soil test to determine fertilizer and lime requirements, and as a general rule, working roughly 3 to 4 pounds of 5-10-10 fertilizer into every 100 square feet of garden area.
Lettuce subjected to high temperatures, particularly at night, may bolt, or go to seed, and leaf lettuce is more prone to bolting, or going to seed, than other types. At this stage, the lettuce develops a bitter flavor that can be somewhat remedied by refrigerating them for at least a day after harvest. When lettuce bolts, its stalk grows to twice the height of the plant, or 12 inches or more, and produces flowers that, if left to their own devices, eventually produce seeds. The natural bitterness in lettuce increases substantially during this stage. Bolting can be minimized by growing bolt-resistant varieties, growing leaf lettuce during cooler weather and shorter days, and keeping it well watered.
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