Lett-uce Grow Lettuce There are many different types of lettuce, but all of them do best in cool temperatures, between 45 and 75 degrees- best suited for the Spring and Fall seasons. The type of lettuce you select will fall into one soil like Coast of Maine Quoddy Mix and plant food such as Garden-tone from Espoma. Plant. Transplant seedlings as early as the ground can be worked, or plant seeds according to the directions on the back of the packet. Space plants roughly 8″ apart. Keep an eye on the temperatures until frost danger has passed. Seedlings can survive 20 degree temperatures if covered protected with a row cover or a sheet/towel. Water. Depending on springs rainfall, lettuce needs deep watering once per week. Deep watering means soaking the ground around the seedlings until water penetrates 4-6″ below. Harvest. Lettuce types mature at different rates, but you can harvest lettuce as soon as leaves form. Trim heads off at the base, or just trim outer leaves on loose-leaf as needed.