Lettuce grows best in cool weather in the spring and in the fall. Some varieties such as endive and radicchio can withstand a moderate amount of frost, but be careful. Using a cold frame or cloche over early spring and late fall plantings can extend your growing season.
Soil with lots of organic matter that drains freely is best. Add compost and lime. One cup of complete organic fertilizer per 3 m (10') will give adequate nutrition.
Either direct seed or start indoors and transplant. Plant seeds approx. 1/4 inch deep and gently tamp down. Seeds sprout in 2 - 15 days, depending on soil temperature, but unlike most seeds, lettuce and its relatives don't like warm soil. You can get around this by sprouting them indoors in a cool area, or pre-sprout by sprinkling seeds on damp paper towel placed in a plastic bag in the fridge for a few days. One gram of seeds sows at least 10m (35') of row, so don't plant the whole package at once. In hot weather, lettuce goes to seed quickly, so have new plantings ready to go.
Seedlings should be hardened off by reducing water and putting the plants outdoors in a sheltered location for 2 to 3 days before transplanting. Thin or transplant loose-leaf types to 20 - 25cm (8 - 10") apart. Heading types should stand about 30cm (12"). Water regularly to prevent leaves from becoming bitter.
Rapid, continuous growth is essential for good yields and high quality. Fall plantings can be protected from rain by putting a cloche over them. Endive heads can be blanched to reduce bitterness by placing a cardboard or plastic disk on top. Radicchio requires a good supply of phosphorus and potassium, but will not head and may bolt if there is too much nitrogen available.
Diseases & insects
Crop rotation is good for disease prevention. Tipburn (tips of leaves turn brown) is caused by a calcium deficiency. If you have limed, tip burn can be caused by nutrient imbalances or lack of moisture. Slugs are a problem in early and late plantings. Clean up their hiding places to reduce the little munchers. Molds & rot from heavy rains can be prevented by growing under a cover.
Pick individual leaves or wait and harvest full heads. Summer lettuce stays in prime eating condition only a short time, so harvest promptly and keep planting. In fall and winter the plants stay in good eating condition longer.