Lettuce

SCIENTIFIC NAME:
Lactuca sativa

CULTURE:
Lettuce is a hardy, cool-weather crop and can be planted with your earliest worked soil. It grows best at 60–65°F (16–18°C) and germinates best below 70°F (21°C), so careful variety selection is key for success in hotter weather. Sow every 2–3 weeks for a continuous supply of either full heads or salad mix.

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 for HEAD LETTUCE:
3–4 weeks before field planting, sow in 128-cell trays barely covered with vermiculite or fine soil. If necessary, utilize shade and frequent misting to keep trays cooled below 75°F (25°C) during germination. Young plants properly hardened at least 3–5 days before planting can survive temperatures as low as 20°F (-6°C). Transplant iceberg, romaine, and butterhead lettuce 10–12" apart in rows 15–18" apart, other types 8–10" apart in rows 12–18", and mini heads as close as 6" in a grid.

DIRECT SEEDING for BABY LEAF:
Seeds can germinate well in soils as low as 40°F (4°C) but often poorly above 75°F (24°C). Sow 4–6 seeds/inch in rows at least 2" apart. Cover lightly to 1/8" and firm gently. Dry soil must be watered to ensure coolness and moisture for uniform germination.

HARVEST:
Head Lettuce: Cut at base, keeping wrapper leaves for handling loss. Consider cutting alternating plants to extend harvest window, allowing remaining plants to continue to grow. Pack heads in layers facing cut ends away. Wash off sap and cool immediately to prevent staining and dehydration. Baby Leaf: Harvest about 1" above the growing point when leaves reach desired harvestable length, about 3–4" long. Remove harvest debris to improve regrowth quality.

STORAGE:
Keep cold at 35–40°F (1–4°C) with high humidity but free of standing water. Head Lettuce: Keep 14–20 days, less for delicate types like butterhead and oakleaf, and longer for lettuce grown slowly in cooler temperatures. For one-cut types, extend season in cold weather by holding cut heads in cooler up to two weeks to process into salad mix.

DAYS TO MATURITY:
From date of cool weather, spring transplanting. Subtract 10–14 days for late spring or early summer, warm weather transplanting. Add about 14 days for direct seeding.