The secret to growing succulent, tasty leaves and preventing premature bolting is to keep lettuce growing fast. Bitterness naturally occurs in older plants. It also develops in drought-stressed young plants because a lack of water causes lettuce to slow its growth and signals the plant to produce more latex, a bitter milky sap. "If you can keep your soil at a moist sponge level, the lettuce will grow continuously to harvest," Stonaker says. "Lettuce that wilts is much more likely to bolt and taste bitter." Conserve water by using soaker hoses or drip tape to irrigate lettuce.
Mulching your lettuce bed does help keep the soil moist, but it attracts slugs and snails, and straw and grass mulch tend to blow into lettuce heads, making postharvest cleaning a chore. Rather than mulching, plant your lettuce a bit closer together, Stonaker suggests. "Lettuce makes a little microclimate for itself when planted together," he explains. "In densely planted beds, the lettuce keeps the soil cool and moist."
Lettuce grows quickly and typically does not need additional fertilizer during the growing season. In fact, fertilizing too much causes the plants to produce very lush leaves that attract aphids. Gardeners can avoid most lettuce problems, including tip burn, bitterness, and fungal disease, by planting lettuce in a site that features full sun and well-drained soil with balanced fertility and by keeping the soil consistently moist but never soggy.
Harvest lettuce in the morning, when the plants' cells are fully hydrated. For head and whole-leaf lettuce plants, slice the plant off at the soil line with a sharp knife. Pinch off individual leaves of leaf lettuce as needed and use scissors to cut baby-sized lettuce. "We aim to cut baby lettuces when they are about 4 inches high," Dawling says. "We cut off about 3 inches and leave an inch." After harvesting baby lettuce, pour diluted fish emulsion on the row to encourage the greens to regrow quickly.
Hold off on washing lettuce until just before eating, because damp greens deteriorate much faster in storage than dry ones. Lettuce stays fresh for two weeks or longer if wrapped in plastic and placed in the crisper drawer of the refrigerator, but it tastes best, and is most satisfying, when eaten fresh.