 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 . 
