Lettuce

Lettuce is grown across a range of types and systems, from field-grown crisphead lettuce harvested by machine to hydroponically grown leaf and butterhead types marketed as living lettuce or pre-packaged greens.

Because the crop matures quickly and is often grown in successive plantings to maintain continuous supply, timing, spacing, and post-harvest handling are closely managed to align with market demand.

Family

Asteraceae (daisy family)

Genus and species

Lactuca sativa

Growth habit

Annual forming a rosette or compact head of leaves; bolts to a flowering stalk under long days and heat

Common types

Crisphead, romaine, butterhead, loose-leaf, and stem (celtuce) types

Cultivated lettuce is derived from wild Lactuca species native to the Mediterranean and Near East, with cultivation recorded in antiquity in Egypt and later spreading through the Mediterranean, Europe, and eventually worldwide.

Lettuce is now grown across a very wide range of countries and production systems. Current statistics on planted area, production, and trade by country are compiled by FAO and national agricultural agencies.

Lettuce is a cool-season crop that grows best within a moderate temperature range; heat and long day length together trigger bolting, in which the plant elongates and flowers, ending marketable leaf or head production.

Because bolting sensitivity varies by cultivar, cultivar selection and planting timing are matched to local season length, and protected culture is used in many regions to extend production into warmer or cooler periods.

Lettuce performs best on fertile, well-drained loams and sandy loams with high organic matter content and reliable moisture-holding capacity, reflecting its shallow root system and rapid growth rate.

Lettuce is established from direct seeding or transplants, often in successive plantings spaced over time to provide continuous harvest. Because the crop competes poorly with weeds during its short cycle, early weed control is important.

• Cultivar selection matched to bolting tolerance and intended production season
• Successive plantings to spread harvest over an extended period
• Close spacing management appropriate to head or leaf type
• Prompt weed control given the crop’s short growing cycle and shallow rooting

Nitrogen availability strongly influences leaf growth rate and quality, while calcium availability in the growing tissue is linked to tipburn, a physiological leaf-margin disorder. Requirements depend on soil or nutrient-solution supply, cultivar, and production system.

Because of its shallow root system and high water content, lettuce requires frequent, consistent irrigation; moisture stress can reduce quality and increase the risk of tipburn and bitterness. Drip and sprinkler irrigation are both used in field production.

Crop water requirements in open-field production are estimated from evapotranspiration and local climate data, following methods published by FAO and national agricultural agencies.

Downy mildew is a major foliar disease of lettuce in cool, humid conditions, and gray mold (Botrytis) can affect leaves and heads, particularly under damp conditions or in storage. Aphids, cutworms, and slugs are among the common pests affecting establishment and leaf quality.

Management combines resistant cultivars, sanitation, field or greenhouse monitoring, and, where warranted, locally authorized control measures applied according to their labels.

Lettuce is harvested at the target leaf or head size before bolting begins, either by cutting the whole head or plant or by repeated leaf picking in cut-and-come-again systems. Rapid post-harvest cooling is important to maintain quality given the crop’s high water content and perishability.

• Fresh use in salads, sandwiches, and as a garnish
• Pre-cut and packaged salad and salad-mix products
• Cooked or grilled use in some cuisines
• Living lettuce sold with roots intact from hydroponic systems in some markets