Lettuce is one of the most widely consumed salad vegetables in the United States and is adapted to cool growing conditions. Optimal temperatures for vegetative growth generally range from 60 to 65°F. Prolonged exposure to high temperatures, particularly when accompanied by warm nights, promotes bolting and reduces head quality. Many modern cultivars can tolerate short periods of daytime temperatures in the 80–85°F range if adequate soil moisture is maintained and nighttime temperatures remain cool.

Lettuce seed can germinate at temperatures as low as 35°F; however, optimal germination occurs between 70 and 75°F. Germination may be reduced under high soil temperatures due to thermoinhibition. Hardened plants can tolerate light freezing, but repeated or prolonged exposure to subfreezing temperatures can result in significant injury or crop loss.

Lettuce has a relatively high water requirement, and even short periods of moisture stress can severely limit growth and head development. Supplemental irrigation is often essential to maintain consistent growth and reduce the risk of crop failure, particularly on well-drained soils.

Considerable variation exists among lettuce types and cultivars in heat tolerance, which largely determines their suitability for warmer production environments. In North Carolina, lettuce can be grown as a spring and fall crop in eastern regions of the state. In the Piedmont, production is best suited to late spring and early fall. In western North Carolina, lettuce can be grown during midsummer. Romaine generally tolerates more heat than head lettuce, while butterhead and leaf types are typically the most heat-tolerant and have the longest potential production window.

Use high-quality, pathogen-tested seed obtained from reputable suppliers. Most commercially available lettuce seed is routinely tested for lettuce mosaic virus (LMV) and other seedborne pathogens; however, growers should confirm seed health status with their supplier, particularly when producing transplants.

Cultivar performance varies by lettuce type, planting season, and disease pressure. The cultivars listed below are recommended for North Carolina based on regional land-grant evaluations and include selections with documented tolerance or resistance to bolting, tipburn, and major diseases such as downy mildew and lettuce mosaic virus.

Green Leaf Lettuce

Recommended cultivars include Grand Rapids, Green Star, Nevada, Salad Bowl, Slobolt, Tango, Tehama, Tropicana, and Two Star. Several of these cultivars offer bolting tolerance and improved resistance to tipburn and downy mildew, making them suitable for spring and fall production in North Carolina.

Red Leaf Lettuce

Recommended cultivars include Cherokee, New Red Fire, Pomegranate Crunch, Red Express, Red Sails, and Ruby. These cultivars provide improved color stability and bolting tolerance, with several also exhibiting resistance to downy mildew and tipburn.

Romaine (Cos) Lettuce

Recommended cultivars include Bluerock, Coastal Star, Green Forest, Green Towers, Parris Island Cos, Salvius, Sparx, Truchas, Valley Heart, and Winter Density. Romaine types generally tolerate higher temperatures than head lettuce and are well suited for spring and fall production across much of the state.

Butterhead (Loose-Head) Lettuce

Recommended cultivars include Adriana, Buttercrunch, Ermosa, Esmeralda, Harmony, Nancy, and Sangria. Butterhead types typically exhibit greater heat tolerance than crisphead lettuce and are well adapted to extended production windows.

Salanova® Types

Salanova® cultivars are increasingly used for both baby leaf and full-head production due to uniformity and disease resistance. Recommended cultivars include Salanova Green Batavia, Salanova Red Batavia, Salanova Green Butter, Salanova Red Butter, Salanova Green Oakleaf, and Salanova Red Oakleaf. These cultivars offer strong resistance to downy mildew and are well suited for high-density plantings.

Important Notes for Growers

• Cultivars differ in resistance to bolting, tipburn, downy mildew, lettuce mosaic virus, and tomato bushy stunt virus.

• Some cultivars are recommended only for fall production due to bolting susceptibility.

• Because disease pressure and seasonal conditions vary across North Carolina, growers are encouraged to trial multiple cultivars and consult the most recent Southeastern U.S. Vegetable Crop Handbook when making final selections.

Successful lettuce production depends on maintaining rapid, uninterrupted vegetative growth. Lettuce can be grown on a wide range of well-drained soils but performs best on fertile soils with adequate organic matter and good water-holding capacity.

Adequate nutrition and a consistent moisture supply are essential. A soil test is the only reliable method for determining lime and fertilizer requirements and should be conducted well in advance of planting. Soil samples can be submitted through the local Cooperative Extension center for analysis and interpretation.

For commercial production, soil pH should be adjusted to a target range of 6.0 to 6.7. Phosphorus and potassium applications should be based on soil test recommendations, as excessive application provides no yield benefit and may increase environmental risk. Nitrogen requirements are moderate and are best met through split applications. A portion of the required nitrogen should be applied preplant, with one or more sidedress applications made during early crop development, depending on growth rate and crop appearance.

Total nitrogen requirements for lettuce in North Carolina typically range from 80 to 120 lb N per acre, depending on lettuce type, soil texture, and production system. Head lettuce types, including crisphead and romaine, generally require 100 to 120 lb N per acre, while leaf lettuce types require slightly less nitrogen due to their shorter production cycle. Nitrogen should be applied in split applications, with approximately 30 to 50 lb N per acre applied preplant and the remainder applied as one or two sidedress applications during early to mid-season growth. On sandy or well-drained soils, additional emphasis should be placed on split applications to reduce nitrogen losses and improve uptake efficiency. Excessive nitrogen should be avoided, as it can increase the risk of tipburn, reduce head quality, and contribute to nutrient leaching.

Lettuce spacing varies by type and production system. Leaf and butterhead lettuce are commonly planted in three to four rows per bed, with beds spaced 66 to 72 inches on center. Within-row spacing typically ranges from 9 to 12 inches, depending on cultivar and target head size. Endive and escarole are planted using a similar bed configuration, with three to four rows per bed on 66- to 72-inch centers, but require wider in-row spacing of approximately 9 to 15 inches to accommodate larger plant size. Plastic mulch is often used to improve weed control and moisture conservation; black plastic is recommended for spring plantings, while white or reflective plastic is preferred when mean daily temperatures at planting exceed 85°F to reduce soil heat buildup and minimize heat stress.

Planting dates for lettuce in North Carolina vary by lettuce type and region. For leaf and butterhead lettuce, spring planting in eastern North Carolina typically occurs from early February through mid-April, with fall planting recommended from late August through early October. In western North Carolina, spring planting generally begins in early March, and production can extend through summer at higher elevations; fall production is not recommended in most western locations due to early frost risk. Romaine (cos) lettuce follows a similar pattern, with spring planting in eastern North Carolina from early February through early April and fall planting from late August to mid-September, while western North Carolina plantings are best suited for spring through midsummer only. Endive and escarole are planted slightly later in the spring, from late March through mid-June in eastern North Carolina and from early May through mid-August in western North Carolina, with fall planting in the east typically from early August to mid-September. Because lettuce is sensitive to heat and bolting, planting dates should be adjusted based on local temperature conditions and cultivar heat tolerance.

Lettuce transplants for commercial production are typically produced in plug trays using a soilless growing medium. Trays containing 128 to 200 cells are commonly used, depending on desired transplant size and planting density. In heated greenhouses, lettuce transplants generally reach suitable size within 4 to 6 weeks after seeding. Temperature, fertility, and irrigation should be managed to promote steady growth while avoiding excessive elongation.

To reduce transplant shock, seedlings should be hardened prior to field establishment by gradually exposing them to outdoor conditions and slightly reducing irrigation for 5 to 7 days before transplanting. Proper hardening improves transplant survival and establishment, particularly under variable spring or fall field conditions.

Lettuce has a shallow and relatively weak root system, with most active roots located in the upper 6 to 12 inches of soil. As a result, the crop is highly sensitive to short periods of water stress, particularly during rapid leaf expansion and head formation. Consistent soil moisture is essential to maintain uninterrupted growth, maximize head size, and preserve quality.

Irrigation should be managed to keep soil moisture near field capacity while avoiding prolonged saturation, which can reduce root function and increase the risk of root and crown diseases. On well-drained sandy or sandy loam soils common in much of North Carolina, frequent but moderate irrigation events are often required. Deep, infrequent irrigations that exceed the effective root zone should be avoided, as they increase nutrient leaching and provide little benefit to the crop.

Drip irrigation is generally preferred for lettuce production because it provides uniform moisture delivery, improves water-use efficiency, and reduces leaf wetness, thereby lowering disease pressure. Overhead irrigation can be effective during stand establishment and for transplant setting, but extended use may increase the risk of foliar diseases and reduce irrigation efficiency under windy or high-temperature conditions. When overhead irrigation is used, applications should be timed to allow foliage to dry quickly.

Soil moisture sensors can be valuable tools for scheduling irrigation, particularly on coarse-textured soils. Sensors installed at 4 to 6 inches and 8 to 12 inches depths can help growers determine when irrigation is needed and verify that water is reaching the active root zone without excessive deep percolation. Irrigation should be initiated before visible wilting occurs, as even brief stress can reduce yield and head quality.

Water requirements increase substantially during warm, sunny conditions due to higher evapotranspiration rates. During periods of elevated temperatures, irrigation frequency may need to increase to prevent stress and reduce the risk of bolting and tipburn. However, excessive irrigation under hot conditions should still be avoided, as calcium-related disorders such as tipburn are influenced by both water availability and plant growth rate.

Lettuce is subject to attack by several insect pests, including aphids, armyworms, imported cabbageworm, and loopers. Pest pressure is generally greater in summer and fall plantings than in spring due to higher temperatures and increased insect activity. Thrips and other occasional pests may also cause damage under favorable conditions.

Several diseases can affect lettuce at different growth stages. Damping-off, caused by soilborne pathogens, is a serious concern during germination and early seedling development. On mature plants, downy mildew, bottom rot, and lettuce drop (Sclerotinia) can significantly reduce yield and marketability, particularly under cool, wet conditions.

Effective pest management relies on an integrated approach that includes regular scouting, accurate diagnosis, use of resistant cultivars when available, cultural practices that reduce pest pressure, and timely application of labeled pesticides when thresholds are exceeded. Growers should consult their local Cooperative Extension office and the current Southeastern U.S. Vegetable Crop Handbook for up-to-date recommendations on pest identification, management options, and resistance management strategies.

Head lettuce is typically ready for harvest approximately 70 to 80 days after seeding or 60 to 70 days after transplanting, depending on cultivar and growing conditions. Heads should be harvested when firm and well formed, leaving three to four wrapper leaves to protect the head during handling. Leaf lettuce generally reaches marketable size in 50 to 60 days after seeding or 30 to 45 days after transplanting and may require harvesting every two to three days during periods of rapid growth.

Harvested lettuce should be shaded immediately to minimize heat buildup and quality loss. Packing may occur in the field or in a nearby shaded packing area, depending on operation size and logistics. Head lettuce is commonly packed in waxed or corrugated cartons designed to prevent head deformation, using flat-pack configurations to avoid crushing. Heads are typically packed in alternating orientations to minimize sap transfer and mechanical damage, and all heads within a carton should be uniform in size and maturity.

Whole-plant leaf lettuce is often sleeved or bagged and packed in fiberboard cartons, while butterhead lettuce may be sleeved or packed similarly to head lettuce. Packaging type, carton size, and pack count should be selected to meet buyer specifications and maintain product quality through distribution.

Lettuce should be cooled as quickly as possible after harvest to remove field heat and maintain quality, particularly when the crop is intended for shipment beyond local markets. Vacuum cooling is the primary method used in major lettuce-producing regions; however, for most North Carolina operations, forced-air cooling in a refrigerated room is the most practical and effective option. Cartons should be properly vented and stacked to allow cold air to be drawn through the containers using high-velocity fans.

Internal head temperature should be reduced to approximately 34 to 38°F as soon as possible after harvest. For longer-term storage, temperatures near 32°F with relative humidity around 95% are optimal. Under these conditions, head lettuce can be stored for approximately 2 to 3 weeks, while leaf and butterhead types generally maintain acceptable quality for 1 to 2 weeks. Care should be taken to avoid freezing injury and excessive moisture loss during storage.