Whether you prefer green or red, leafy or crisp, growing your own lettuce (Lactuca sativa) gives you many options in the garden. Head lettuce forms tight round heads and provides the optimum in crispness, while looseleaf lettuce comes in a variety of colors and provides a flavorful addition to salads. Romaine varieties feature both a loose head and leafy tops. Determining when your lettuce is ready for picking depends on the variety.
Monitor the size and formation of the lettuce heads beginning about 55 days after planting, which is when most head lettuce varieties approach maturity. Check the lettuce daily for ripeness.
Select lettuce that has reached its full size and formed a firm head. Verify that the outer wrapper leaves have begun to overlap.
Cut through the stem beneath the lettuce head, slicing at the soil surface, with a sharp knife. Trim any remaining stem from the head lettuce so the cut is flush to the head.
Harvest looseleaf lettuce plants when the foliage grows 5 to 6 inches tall, which may require up to 75 days. Allow romaine lettuce varieties to form a 6- to 8-inch tall upright head that's solid near the bottom and loose on top.
Cut of the outer leaves of looseleaf lettuce once they reach their mature length. Snip through the leaves with shears near the base of the plant. Leave the inner foliage to continue growing. Harvest outer leaves every one to two weeks as they are replaced with new foliage.
Pick the entire looseleaf or romaine lettuce plant when it reaches its mature height. Cut through the base of the plant at soil level, using a sharp knife.