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 16-18C. 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 16-20C. 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/2.5cm., or in 19mm 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 24C, until germination. If sowing into flats, transplant 2.5-5cm 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 -6C. Transplant iceberg and romaine lettuce 25-30cm apart, in rows 45cm apart. Other types 20-25cm apart in rows 30-45 apart for full-size heads or 15cm apart for mini heads.
DIRECT SEEDING: Seeds germinate even at low, 4C, soil temperature, but poorly above 24C depending on the variety and seed lot. Sow seeds 25mm apart, rows 30-45cm apart. Cover seed lightly, about 3mm, and firm soil gently. Thin iceberg and cos lettuce to one plant every 20-25, other types 20-25cm for full-size heads or 15cm for mini heads. Dry soil must be watered to ensure coolness and moisture, and for uniform germination.
SALAD MIX/BABY LEAF: Sow in a 5-10cm wide band, about 60 seeds/30cm
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/70m, 28g/1.75km, 150g/acre @65mm apart in rows 45cm apart. For baby leaf: 1,000 seeds/5m, 30g/120m, 500g/2km at 60 seeds/30cm.
