Many beginning AeroGardeners wonder when it's time to start harvesting.  If your plants are old enough for you to ask the question, you're probably ready!  Begin harvesting lettuce when leaves are about 3 inches tall.  Pick the leaves you'd like to eat and leave the rest to grow.  Just never harvest more than 1/3 the plant at any given time.  Picking the bigger leaves allows more light to reach other leaves, making everything grow faster.  Waiting too long to harvest actually hurts your lettuce yields.  Start with smaller yields as snacks or on sandwhiches, then as plants grow faster, work up to salads.