 A hardy annual , some varieties of lettuce can be overwintered even in relatively cold climates under a layer of straw , and older , heirloom varieties are often grown in cold frames . Lettuces meant for the cutting of individual leaves are generally planted straight into the garden in thick rows . Heading varieties of lettuces are commonly started in flats , then transplanted to individual spots , usually 8 to 14 inches ( 20 to 36 cm ) apart , in the garden after developing several leaves . Lettuce spaced further apart receives more sunlight , which improves color and nutrient quantities in the leaves . Pale to white lettuce , such as the centers in some iceberg lettuce , contain few nutrients . 
