Crisp and refreshing leaves of lettuce (Lactuca sativa) provide the basis for a great salad, which is made all the more tasty if you grow the lettuce yourself. Leaf lettuce varieties don't form a head so there's no need to harvest more than you need. You can pick leaves as necessary or you may cut the plants back for a larger harvest later. They will regrow new leaves to supply you for several weeks. Cutting lettuce correctly prevents damage to the plants and helps encourage further growth.
Snip off the outer leaves of each lettuce plant once they grow a length of 4 to 6 inches, which should take approximately 35 to 50 days after sowing the seeds. Leave the inner foliage on the plants so they can continue growing.
Cut back the entire plant within 2 to 3 inches of the ground, leaving the bottom leaves and the crown of the plant intact. Cutting back will provide a larger harvest than individual leaf removal.
Sprinkle ¼ cup of 21-0-0 fertilizer for every 10 feet of lettuce row after cutting the plants back. Apply the fertilizer 6 inches from the base of the lettuce plants and water it in thoroughly. The fertilizer provides nutrients that help feed a new flush of leaf growth.
Harvest the lettuce a second time once it grows 4 inches tall by cutting it back or removing the outer leaves. You can often get multiple harvests from the plants because they continue to produce until they set seed, which usually occurs when temperatures rise above 75 degrees Fahrenheit.