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.
Inspect the lettuce plants for leaves that are ready to harvest. Most leaves are mature enough once they reach 1 to 3 inches long, but they should still be tender up to 6 inches long. Cut off the outer leaves of the plants with a small pair of garden shears to harvest just a few leaves.
Growing Head Lettuce. 1  1. Choose a head lettuce variety for indoor planting. Head lettuces take longer to mature. 2  2. Prepare seed trays. You can start your lettuce seeds in store-bought seed trays or make your own out of an old egg carton, box or newspaper. 3  3. Sow the seeds 4-6 weeks before the last spring frost.