Description
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 1″ apart, 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.
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/220′, 1 oz./5,300′, 5 1/2 oz./acre 2 1/2″ apart in rows 18″ apart. For baby leaf: 1,000 seeds/16′, 1 oz./400′, 1 lb./6,400′ at 60 seeds/ft.
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