All types of lettuce have tiny seeds and shallow root systems that do not compete well with weeds. Market gardeners use a technique called stale bed cultivation to create fine, weed-free soil for lettuce, and this system will work well in your home garden, too.
Start by weeding your lettuce bed thoroughly three weeks before transplanting or direct-sowing. Spread compost 1 inch thick over the soil and dig it in. Rake the bed until the soil is smooth, crumbly, and free of clods, rocks, and crop debris. Then water the bed well. "Let the first flush of weeds come up, and then cultivate lightly," says Frank Stonaker, the lead researcher for the lettuce Bolting Resistance Project at Colorado State University and the coordinator of the university's specialty-crops program. "A stirrup hoe is a nice tool for cultivating, because it cuts about 1/4 inch deep in the soil and gets rid of small weeds without disturbing the soil enough to bring up new weed seeds."
Begin sowing lettuce seed in spring as soon as the ground thaws and the soil is dry enough to rake. Lettuce needs light to germinate, so sprinkle the seeds on top of finely prepared, moist soil and cover them with an extremely light layer of screened compost or a little seed-starting mix. Sow lettuce in rows 10 to 12 inches apart if you plan to harvest mature plants. Thin the stand when the seedlings have three or four leaves, using the tender thinnings in salads. For baby lettuces, sow seed in 3-inch-wide bands, spacing the bands 8 to 10 inches apart. Hold off on thinning baby lettuces, because you want them to grow into a thick strip of greens for harvesting.
Now, here's one of the tricks to successfully extending your lettuce-eating season: About two to three weeks before sowing lettuce seeds directly in your garden, start some in trays inside. Then transplant the seedlings outside at the same time you direct-sow seed. "With transplants, you get more crops from one growing season, because they are in the ground for less time," says Pam Dawling, an organic gardener who manages the 3 1/2-acre food garden at the Twin Oaks intentional community in Louisa, Virginia.
When planting seedlings, water them well 24 hours before setting them out and again one hour before planting. "The goal is to have the plants absorb the maximum amount of water," Dawling explains. Watering well before planting protects the plants from wilting at transplant, she notes.
Transplant the seedlings when they have four to six true leaves. Be sure to harden off both purchased and homegrown seedlings before transplanting by gradually exposing them to outdoor conditions over a period of five to seven days. "I prefer to plant in the late afternoon or evening," Stonaker adds. "That way the transplants don't bake all day in the sun."
Give the transplants a kick start after planting by watering them in with diluted fish emulsion. When thinning directly sown plants or transplanting seedlings, leave 8 to 12 inches between Batavians, romaines, and crispheads, 6 to 8 inches between butterheads, and 4 to 6 inches for full-grown leaf lettuces.