Lettuce requires cool temperatures of 15-20^oC. The iceberg varieties will not form heads in hotter conditions. It is a rapid growing crop with a life-cycle of 45-70 days from seeding/planting to harvest. Lettuce is a shallow-rooted crop, and a fine seedbed is needed to allow the roots to establish and grow. Lettuce grows best on light, well-drained fertile soils, with a pH of 6.0-7.0. Field lettuce needs to be sown on raised beds to aid water infiltration and retention, and allow adequate soil aeration and drainage. Lettuce is highly sensitive to salinity. Soils with an electrical conductivity of 2 or less are highly desirable. As shown in the following table, lettuce is a heavy potassium feeder, it requires triple the amount of K than N. Some types of lettuce do very well when grown in hydroponics systems.