Lettuce is a cool-season crop that performs best in milder temperatures. The timing of the harvest directly impacts the flavor and crispness of the final product, as quality quickly declines when conditions become too warm. Understanding your variety’s growth habit ensures a tender, flavorful yield and can help extend the harvest window.
Harvesting Leaf Lettuce
Loose-leaf varieties, such as Black Seeded Simpson or Salad Bowl, are harvested using the “cut-and-come-again” technique, allowing for multiple harvests. Begin harvesting when the outermost leaves reach four to six inches long. This ensures the leaves have developed their full flavor and texture.
This method requires cutting only the outer, mature leaves and leaving the central growing point, or crown, intact. Use a sharp knife or clean scissors to snip the leaves about one inch above the soil line. Harvest no more than one-third of the total foliage at one time. This restraint allows the plant to continue photosynthesizing efficiently and produce subsequent flushes of new growth.
Harvesting Head Lettuce
Varieties that form a dense, compact structure, including Romaine, Iceberg, and Butterhead, require a different approach. The primary cue for harvest is firmness, indicating the head is fully formed and the leaves are tightly packed. Gently squeeze the side of the head; it should feel dense and solid, not loose or airy.
For most headed varieties, the harvest is a one-time event that removes the entire plant. Use a sharp knife to sever the stem cleanly just above the soil line. Leaving the lower stem and root system can sometimes lead to a small secondary growth of leaves. However, the initial, tightly-formed head represents the peak quality harvest.
Recognizing the End of the Harvest Window
The most significant signal that the harvest window is closing is bolting, the plant’s natural transition from vegetative growth to reproductive growth. Bolting is visually indicated by the rapid elongation of the central stalk, which pushes upward from the center of the rosette.
This shift in the plant’s focus is accompanied by a change in its chemical composition. The plant increases its production of bitter-tasting compounds, primarily a sesquiterpene lactone called lactucin. When the plant bolts, the concentration of lactucin increases significantly throughout the leaves, making the lettuce unpalatable.
Bolting is typically triggered by environmental stress, most often high temperatures and longer daylight hours. Once the central stalk begins to rise, the leaves quickly become tougher and the bitterness intensifies. Harvesting the entire plant immediately upon seeing the first sign of stalk elongation is the only way to salvage the remaining edible portion before lactucin levels rise too high.