Leaves are eaten raw. Lettuce thrives under cool, humid conditions and can survive a light frost. Long, hot days generally prompt plants to bolt: the sap in the leaves turns unpalatably bitter and the harvest ends. It needs regular watering and welcomes shade from taller crops. A rich, loose soil with a pH between 6.0 and 7.0 is ideal. Lettuce has a high water content and also contains vitamins A, C, and K, folacin, iron, calcium, fiber, potassium, and copper.