Planting: For direct seeding, seeds germinate at low soil temperatures (40°F), but poorly above 75°F. Sow seeds 2-3″ 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. For transplanting, sow 2-3 seeds per cell, 1/4″ deep, 3-4 weeks before transplanting outdoors. Do not let soil above 70F while germinating so keep out of sun and a cool, dark location. 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. 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.
Watering: Water lettuce once to twice per week or every 4 days whenever rainfall is inadequate.
Fertilizer: Lettuce is typically a care-free plant, but you can fertilize the soil with an organic fertilizer one week prior to planting the seeds. Lettuce grows best in soil that is high in humus. Fertilize three weeks after transplanting seedlings with an alfalfa meal or a slow-release fertilizer.
Days to Maturity: Lettuce can be picked whenever real leaves form. Pick when the leaves are younger rather than waiting so the taste doesn’t become bitter. (See each variety for days to maturity)
Harvesting: For heads of lettuce, cut the plant at the soil line to harvest it. For leaf lettuces, you can harvest the entire plant or only the outer leaves as needed. Harvest in the morning. Store in cool, dark and high humidity location for up to 2-3 weeks.
Tips: Plant lettuce near taller plants, like tomatoes, so the leaves are in the shade during the hot parts of the day.