To define a number range, you have to create a new number interval: 1  Specify an alphanumeric key with up to 2 characters. 2  Specify the limits of the number interval.  Mark the number range if it is planned for external number assignment.
3. Trim back the entire plant when it reaches 3 to 6 inches high, or approximately every 10 days. Cut back to within 1 to 2 inches of the ground. Most loose-leaf lettuce varieties grow back from a severe trim to produce more leaves.
Step 3. Photo Credit Stephanie Loaiza/Demand Media. Remove the separate lettuce leaves by hand, if desired, and pat each dry with paper towels or use a salad spinner to free the leaves of as much water as possible. Use paper towels to pat dry the outside of the head of lettuce if you plan on storing it whole.