Lettuce is a rapid growing crop with a life-cycle of 45-70 days from seeding/planting to harvest. It requires a temperatures between 15-20oC  and the iceberg varieties will not form heads in hotter conditions.  It is a shallow-rooted crop and a fine seedbed is needed to allow roots to establish and grow. Lettuce grows best on light, well-drained fertile soils, with a pH of 6.0-7.0. It is very sensitive to salinity and soils with an electrical conductivity of 2 or less are highly desirable. Lettuce is a heavy potassium feeder, as it requires triple the amount of this element as compared to Nitrogen.