Lettuce - Key Growing Information

A field of lettuce being evaluated in trials by our lettuce product tech at our research farm.

SCIENTIFIC NAME: Lactuca sativa
CULTURE: Lettuce is hardy and can be planted as early as the soil can be worked. It is a cool weather crop and grows best at temperatures of 60-65°F (16-18°C). Careful variety selection is important for hot weather plantings. Sow every 3 weeks for a continuous supply of fresh lettuce.
THERMAL DORMANCY: Lettuce seed can enter thermal dormancy when exposed to high temperatures. Optimum germination results at soil temperatures of 60-68°F (16-20°C). The priming process in pelleted lettuce seeds broadens the temperature range in which the seeds will germinate, overcoming some of their thermal dormancy.
TRANSPLANTING: Sow in flats, 4 seeds/in., or in 3/4" plug trays, barely covering seeds with fine vermiculite, 3-4 weeks before transplanting outdoors. Shade the flats on sunny, warm days if necessary to keep the soil surface cool, below 75°F (24°C), until germination. If sowing into flats, transplant 1-2" apart into flats, pots, or cell-type containers about 2 weeks later. Harden seedlings by reducing water and temperature for 2-3 days before planting outdoors. Properly hardened transplants can survive temperatures as low as 20°F (-6°C). Transplant iceberg and romaine lettuce 10-12" apart, in rows 18" apart. Other types 8-10" apart in rows 12-18" apart for full-size heads or 6" apart for mini heads.
DIRECT SEEDING: Seeds germinate even at low, 40°F (4°C), soil temperature, but poorly above 75°F (24°C) depending on the variety and seed lot. Sow seeds 6 seeds per foot, rows 12-18" apart. Cover seed lightly, about 1/8", and firm soil gently. Thin iceberg and romaine lettuce to one plant every 10-12", other types 8-10" for full-size heads or 6" for mini heads. Dry soil must be watered to ensure coolness and moisture, and for uniform germination.
SALAD MIX/BABY LEAF: Sow in a 2-4" wide band, about 60 seeds/ft.
MT0 SEEDS: A variety's description followed by MT0-30 indicates that the seed offered for sale has been tested for the presence of Lettuce Mosaic Virus and that no LMV was found in a sample of at least 30,000 seeds.
NOTE: A disease-free test result does not guarantee a seed lot to be disease-free, only that in the sample tested, the pathogen was not found.
DAYS TO MATURITY: For full-size heads in mild temperatures from direct seeding; subtract 10-14 days if transplanting. NOTE: Maturity can be 3 or more weeks later in cool weather, and up to 1 week earlier in hot weather.
AVG. DIRECT SEEDING RATE: For full-size heads (precision seeded): 1,000 seeds/160', 1 oz./3,000', 10 oz./acre 2" apart in rows 18" apart. For baby leaf: 1,000 seeds/16', 1 oz./400', 1 lb./6,400' at 60 seeds/ft.
TRANSPLANTS: Avg. 16,000 plants/oz.
SEED SPECS: SEEDS/OZ.: Avg. 17,800.
PACKET: 500 seeds, unless otherwise indicated.