Lift the top leaves of lettuce to expose their connection to the stalk just above the roots.
Snip cleanly through and remove each leaf.
Leave the bottom leaves to mature and be sure not to snip too close to the roots, which could damage them. If you are harvesting a lot from one plant, be sure to give it extra nutrients to help it regenerate more leaves.
Harvest the entire plant, roots and all, if growth has slowed down. This may indicate that the roots are rotting out. Remove the container from the hydroponic bed, hold it over some newspaper and pull the entire plant out. Shake off any crushed rock or other excess growth medium and return the container to the bed to plant new lettuce or other plants.
Wash, rinse and pat dry all the leaves. Although no pesticides or organic soil are used in the growing process, environmental dirt and other adulterants can find their way onto the lettuce leaves.