Nutrient Management Research Database

This publication covers the following topics:

• Production areas and seasons
• Climatic Requirements
• Varieties and planting techniques
• Soils appropriate for lettuce production
• Irrigation
• Fertilization
• Integrated pest management
• Harvest and handling

The following are the most important selections from the publication. Make sure to check it out yourself for a more complete picture.

Production areas and seasons

Lettuce is primarily grown in the Central Coast, Southern Coast, Central Valley, and south desert regions.

Season length varies from 65-80 days for midsummer crops to 130 days for late-fall and winter plantings.

Production seasons vary between regions based on differences in seasonal temperatures. 

Climatic Requirements

Lettuce is a cool-season crop that grows best when 73^o F during the day and 45^o F at night. When temperatures are too high, lettuce tends to bolt making the yield unmarketable. Temperatures close to freezing severely stunt growth rates. Below freezing temperatures can damage plants.

Varieties and Planting Techniques

Leaf, romaine, and butterhead lettuce varieties vary in leaf color and shape.

Most leaf lettuce is precision planted as pelleted seed, though transplanting is becoming more popular. 

Rows are either spaced 40 inches apart with 2 seedlines or 80 inches apart with 5-6 seedlines. Full sized lettuce are spaced 2-3 inches apart and later thinned to 10-12 inches. 

Primed seeds are able to germinate at higher temperatures.

Soils

Leaf lettuce will grow best on silt loams and sandy soils. In the Central Coast and Central Valley, heavier textured soils can be used to grow lettuce, as long as there is sufficient soil structure and adequate drainage. 

Irrigation

In the desert regions, leaf lettuce is generally sprinkler irrigated for 5-7 days followed by furrow irrigation.

Most Central Coast fields are pre-irrigated with 2-4 inches of water before seeding. Both seeded and transplanted lettuce are sprinkler irrigated every 2-3 days until emergence. After emergence irrigation frequency is reduced. Surface drip irrigation is also gaining in popularity.

Total irrigation is generally 18-24 inches of water in sprinkler irrigated systems, 24-30 inches in furrow irrigated systems, and 12-18 inches in drip irrigated fields. 

Fertilization

Central and south coast lettuce growers much carefully apply nitrate and phosphorus to comply with water quality standards. In particular, fall nitrogen application should be avoided to limit leaching of N below the crop rooting zone. 

Threshold test result levels have been identified that inform growers when supplemental fertilizer is required to increase yields. These threshold levels are 60 ppm for Olsen-P phosphorus, 150 for ammonium-acetate extractable potassium, and 1.5 ppm for DTPA-extractable zinc.

Lettuce is sensitive to elevate ammonium levels, especially in the early spring. 

Integrated Pest Management

For the most up to date information for pest management, visit the UC-Davis IPM page.