Quick growth makes for good flavor and tenderness, so assure water and fertility. Lettuce seeds will not sprout once temperatures reach 85 F degrees. Putting seeds in a jar, in the refrigerator 4-5 days before planting will aid germination. In summer heat, sow in the evening, water well, and give some shade.
Within each type of lettuce, some are better for planting in each season. Spring lettuces can be planted as early as you can work the soil. Seeds will germinate when soil reaches 45 degress, and transplants will grow in even colder soil as long as days are above freezing. Brief night frost down to 25 F is not a problem. Summer varieties are best planted in succession starting in mid-spring. They are bred to be bolt-resistant under heat stress, though shadecloth will improve quality. Fall vaieties can be planted in pots or flats in a shady place in August, and transplanted into the garden under shadecloth or taller crops. Late fall crops of baby greens and a few ultra-hardy varieties can be planted September/October to stand through late fall, or winter in mild climates.
Lettuce types: Looseleafs make a head that fans out so that the center leaves are visible. They are tolerant of marginal conditions, and can be cut leaf-by-leaf or all at once.
Butterheads have a soft, silky texture and small, rose-like heads.
Bibbs are looser, with the same silky leaf, but a crunchy midrib.
Romaine (or Cos) makes a tall head with crunchy midrib.
Summercrisp types have a tall, ruffled head, with a crisp, somewhat blanched interior.
Iceberg types have a firm, wrapped head, and a dense, blanched, crisp interior.
Stem lettuce is a unique kind that is still good after bolting.
The leaves are widely eaten raw, but can also be boiled at a potherb, pickled, braised, sauteed, fried, pureed, and used in soups and stews. In the Middle East the bulghur wheat salad tabouli is wrapped in lettuce leaves and eaten out of hand. Sprouted seeds can be used in salads and sandwiches.