Producing a successful lettuce crop can be a challenge for home gardeners. Weather is the main problem. All types of lettuce (crisphead, butterhead, leaf or bunching, and romaine or cos) require cool, moist growing conditions. Daytime temperatures of 70 to 75 and nighttime temperatures of 55 to 60 are ideal. Adequate supplies of moisture and nutrients are also important. Lettuce requires one inch of water per week. As with other plants, gardeners will need to water when Mother Nature doesn't supply sufficient rainfall. A complete fertilizer, such as 10-10-10, applied to the garden prior to planting should be adequate for successful growth.
Bolting is a common problem experienced by lettuce growers. Bolting is the undesirable formation of flowers and seeds. Bolting destroys the flavor of the leaves by making them bitter and tough. It is caused by high temperatures, long periods of high light intensities, and drought. Lettuce has an internal counter that keeps track of the number of daylight hours the plant receives. Once a critical number of hours are received, the plant sends up its flower stalk. The exact number of hours varies from cultivar to cultivar. Apparently, lettuce goes through four distinct stages of growth; juvenile/vegetative, adult/vegetative, adult/intermediate, and adult/reproductive. The plant can handle environmental stresses quite well when vegetative. However, once the intermediate stage is reached, environmental stresses, such as high temperatures or drought, will cause the plant to bolt.
Gardeners can reduce the tendency for bolting in various ways. Lettuce can be started indoors under lights to give them an early start and then planted outdoors while temperatures are still cool. When growing lettuce seedlings under lights, do not leave the lights on for more than 12 hours because lettuce needs short days to grow. Row covers, such as Reemay or plastic tunnels, can be used to extend the growing season both in the spring and fall. Late planted lettuce benefits from a shade cloth placed over the row to reduce heat and light intensity. Soil moisture must be kept in constant supply.
Lettuce has evolved considerably since it was first grown by the ancient Egyptians. Today, gardeners can choose from 4 types of lettuce and numerous cultivars. The key to successful production is to provide good growing conditions.
This article originally appeared in the April 6, 1994 issue, pp. 1994 issue, pp. 39-40.