 Lettuce grows best in full sun in loose, nitrogen-rich soils with a pH of between 6.0 and 6.8. Heat generally prompts lettuce to bolt, with most varieties growing poorly above 75°F (24°C); cool temperatures prompt better performance, with 60 to 65°F (16 to 18°C) being preferred and as low as 45°F (7°C) being tolerated. Plants in hot areas that are provided partial shade during the hottest part of the day will bolt more slowly. Temperatures above 80°F (27°C) will generally result in poor or non-existent germination of lettuce seeds. After harvest, lettuce lasts the longest when kept at 32°F (0°C) and 96 percent humidity. Lettuce quickly degrades when stored with fruit such as apples, pears and bananas that release the ripening agent ethylene gas. The high water content of lettuce (94.9 percent) creates problems when attempting to preserve the plant – it cannot be successfully frozen, canned or dried and must be eaten fresh.
