Leaf lettuce, including looseleaf, oakleaf, and certain romaine varieties, is a non-heading type of Lactuca sativa grown for its individual leaves. Since it does not form a compact head, gardeners can begin harvesting much sooner than with types like iceberg. The ability to harvest leaves repeatedly makes leaf lettuce an efficient crop for a continuous supply of fresh greens.
Determining Readiness
The initial timing for harvest is indicated by the plant’s age and physical size. Seed packets typically list 30 to 40 days for the baby leaf stage and 40 to 60 days for full-sized leaves. These ranges are helpful guidelines, but leaf lettuce can be picked at almost any size once the leaves are large enough for a meal.
Physical size is a more practical metric than a calendar date for determining readiness. Leaves should be at least 4 to 6 inches in height before the initial harvest begins. Harvesting leaves at this size yields tender greens, often referred to as baby lettuce. Waiting longer allows the leaves to grow larger and develop a more robust texture, but harvesting should not be delayed past the point of palatability.
The Cut-and-Come-Again Method
The cut-and-come-again method maximizes production by encouraging the plant to regenerate new growth repeatedly. This technique involves taking only part of the plant while ensuring the central growth mechanism remains intact. The most common approach is to harvest the outer, mature leaves, leaving the newer, inner leaves to continue developing. This allows the plant to photosynthesize efficiently while providing a steady supply of greens.
Alternatively, a gardener can cut the entire plant for a larger, single harvest, provided the growing point is preserved. This is done by slicing all the leaves about one to one-and-a-half inches above the soil line. The plant’s central growing point, often called the crown, must be left undamaged at the base for the plant to regrow. The remaining stub will quickly produce a fresh cluster of leaves, often ready for a second cut within a couple of weeks.
Harvesting should be done in the early morning hours before the heat of the day causes the leaves to lose turgidity. Leaves harvested in the cool morning air retain a higher water content, resulting in a crisper texture and sweeter flavor. Using sharp scissors or a clean knife prevents unnecessary damage to the plant tissue and helps stimulate new, healthy growth.
Signs the Season is Over
The continuous harvest season is limited by rising temperatures, as lettuce is a cool-season crop that thrives best between 60°F and 70°F. When the weather becomes consistently hot, typically above 75°F, the plant undergoes a physiological change known as bolting. Bolting is the plant’s shift from vegetative growth to reproductive growth, producing flowers and seeds instead of leaves.
The first visible sign of bolting is the rapid elongation of a tall, central stalk rising from the middle of the rosette. Once bolting begins, the plant directs energy into the seed stalk, causing the leaves to become smaller, tougher, and more pointed. The plant also produces high concentrations of sesquiterpene lactones, which impart a noticeably bitter taste. Once a plant bolts, the leaves become inedible, signaling the productive season is over, and the entire plant should be removed.