Grow Guide Conditions:
Lettuce is a cool season crop and grows best at 60–70°F, but can be planted in early spring as soon as the soil can be worked. Optimum growth occurs on well drained, fertile, high organic matter soils with a pH of 6.0–7.5. Irrigate frequently to provide continuous moisture and cool the soil, but avoid water logging. Seeds do not germinate at temperatures above 90°F. Use shade cloth when sowing in hot weather. See product descriptions for heat tolerant varieties.
Grow Guide Seed:
Lettuce can be direct seeded or transplanted. Plant head lettuces every three weeks for continuous harvests. Sow less frequently during cool spring and fall conditions. Optimum germination occurs at soil temperatures from 60–70°F, but seeds will germinate at as low as 40°F. To start seedlings indoors, fill starter trays with a sterile seed starting mix. Plant 2 seeds per cell, 1/8th inch deep. Thin to 1 plant per cell. Harden-off seedlings for 5–7 days prior to transplanting. Transplant 5-6 week old seedlings outside in a fertile garden bed, 12-15 inches apart, allowing 18-24 inches between rows. To direct seed, plant seed 1/8-1/4 inch deep, 6 seeds per row foot, allowing 18-24 inches between rows. As the plants size up, gradually thin to one plant every 12 inches, eating the thinnings.
See ‘Salad Mixes’ section for baby-leaf growing instructions.
Grow Guide Pests:
Downy Mildew is one of the most serious diseases of lettuce, especially in late summer plantings. Varieties are available with resistance to some or all races of this fungal pathogen (see variety descriptions). Disease pressure for this and other lettuce diseases may be mitigated by increasing row spacing, orienting rows for optimum air flow, using drip irrigation, and practicing crop rotations. Lettuce Mosaic Virus (LMV) is transmitted by many species of aphids. Encourage beneficial insect activity by planting alyssum nearby to suppress aphid populations. Provide adequate Calcium and avoid excessive Nitrogen and Phosphorus to prevent tipburn.
Grow Guide Harvest:
Cut lettuce heads at the base when they reach full size, and when heading varieties feel solid. If let to stand in the garden too long they will start to elongate and go to seed, which turns them bitter. Wash in cold water and store in the refrigerator to crisp up. Tender oakleaf and butterhead varieties are fragile and should be handled as little as possible. Loose leaf types can be harvested gradually by pulling off a few outer leaves at a time, leaving the central heart to continue growing to maturity. This practice will result in smaller finished heads.