A short browse through a seed catalog, seed display rack, or selection of nursery seedlings will reveal enough variety to keep your salad bowl crisp and colorful throughout the growing season.
There are four principal types of lettuce: crisphead, butterhead or Boston, loose-leaf, and romaine.
Crisphead is the most exasperating for home gardeners to produce. Heads form best when monthly average temperatures are 55°–60°F/13°–16°C. In mild climates, this type of lettuce does well over a long season, but in hot summer areas, timing of planting becomes critical. Best varieties include ‘Great Lakes’, ‘Summertime’, and ‘Nevada’.
Butterhead or Boston type has a loose head with green, smooth outer leaves and yellow inner leaves. Good varieties include ‘Bibb’ (‘Limestone’), ‘Buttercrunch’, and ‘Tom Thumb’. ‘Mignonette’ (‘Manoa’) stands heat without bolting (going to seed—a process that causes the leaves to become bitter).
Loose-leaf lettuce makes a rosette rather than a head. It stands heat better than the other types. Choice selections include ‘Blackseeded Simpson’, ‘Green Ice’, and ‘Oak Leaf’ (all with green leaves); ‘Salad Bowl’ (with deeply cut green leaves); and ‘Prizehead’ and ‘Ruby’ (red-tinged leaves).
Romaine lettuce has an erect, cylindrical head of smooth leaves. The outer leaves are green; the inner ones are whitish. It stands heat moderately well. Try ‘Medallion’, ‘Olga’, or ‘Parris Island’.
Lettuces with bronzy to pinkish red leaves add color to a salad. ‘Freckles’, ‘Marveille des Quatre Saisons’, and ‘Perella Red’ are butterheads; ‘Lollo Rosso’, ‘Red Oak Leaf’, ‘Red Sails’, and ‘Ruby’ are loose-leaf varieties; ‘Rouge d’Hiver’ and ‘Sierra’ are romaines.
Various loose-leaf and romaine lettuce varieties are typically included in mesclun mixes—mixtures of fast-growing, tender salad greens (usually some mild and some tangy)—that may include mustards, arugula, cress, chicory, radicchio, and/or mizuna.
All lettuces need loose, well-drained soil. Sow in open ground; barely cover the seeds. Loose-leaf lettuce can be grown as close as 4 in. apart; thin all other types to 1 ft. apart. Grow mesclun in blocks 4 in. wide and don’t thin.
For prolonged harvest, sow at 2-week intervals. In cold-winter regions, begin sowing seed for all types after frost, as soon as the soil is workable; where summers are very short, sow indoors, then transplant seedlings outdoors after last frost.
In mild-winter, cool-summer regions, sow in early spring for spring and summer harvest, then make further sowings in late summer or early fall for winter harvest. In mild-winter, hot-summer areas, grow only as a winter and early spring crop.
Feed plants lightly and frequently. Control snails, slugs, and earwigs. Harvest when heads or leaves are of good size; once lettuce reaches maturity, it rapidly goes to seed, becoming quite bitter.
With loose-leaf lettuce, you can clip off just the outer leaves as you need them. Likewise, snip off young leaves of mesclun mix for salads.