Three-Season Lettuce Plan
Growing lettuce continuously from spring through fall requires planning, because lettuce matures at different rates depending on the season and variety. If your family eats salad every day, plan on growing two heads of lettuce or a 2-foot-long band of baby greens per person each week.
Plant romaine, butterhead, and leaf lettuce seedlings (purchase some from a nursery if you didn't start your own) and direct-seed a week or two before your average last-frost date. In early spring, plant lettuce every two weeks and install a row cover over your plants to moderate air temperature, protect plants from variable weather, and keep out insect pests. As the weather warms, remove the row cover, begin planting every 7 to 10 days, and switch to heat-tolerant varieties.
Lettuce germinates in just three days when the soil is 68°F, but soil temperatures over 85°F signal the seed to go dormant. Overcome this summertime problem by planting seedlings of heat-tolerant varieties, especially Batavians. If you direct-sow, store your lettuce seed in the refrigerator and cool down the soil for a few days before planting. "Water the soil and put down burlap bags to keep the soil moist and dark and cool," advises Pam Dawling, a market gardener in Virginia. In her climate, she also recommends laying ice over rows immediately after sowing.
Transplant and direct-sow lettuce to areas that get shade, such as underneath tomato plants or corn. Be sure to keep up on watering, and harvest lettuce at the baby stage before it has a chance to develop bitter-tasting latex. Make successive plantings every 7 to 10 days in summer.
Gardeners in climates where summer temperatures stay consistently about 85°F can greatly improve yields and quality of summer lettuce by covering it with shade cloth. A study funded by the Organic Farming Research Foundation found that lettuce grown under 40 percent shade cloth from June through August in Kansas had higher yields, grew larger and faster, and produced reliably higher quality greens than lettuce grown in unshaded test plots.
Lettuce takes longer to mature as fall progresses, in response to cooler weather and shorter days. "In the fall, you need to plant more often, because one day's difference in sowing can make a difference of a week in harvesting," Dawling says. Switch to cold-tolerant varieties in late August and sow or plant seedlings at least once a week through the first half of September for harvests that will mature in late November. "Lettuce is very frost-tolerant," says Frank Stonaker, a researcher at Colorado State University. "It can tolerate temperatures down into the 20s." Install row covers over lettuce when nighttime temperatures dip below 45°F to protect the plants from wind and the elements and to keep your garden full of lettuce well into fall.