Snip off the outer leaves within 1 inch of the soil using clean shears, once the leaves reach 4 to 6 inches in length. Use these tender leaves in salads or as a cooked green. Leave the small inner leaves on the plant to grow larger.
Harvest the entire plant if all the leaves have reached the desired size. Cut back the plant to within 2 inches of the ground, taking care not to cut into the crown of the mustard. The plant sends up new leaves from the crown.
Pick leaves from the harvested plants as they regrow and reach at least 4 inches in length. Harvest the leaves singly or cut back the entire plant, as desired.
Dispose of any yellow, wilted or damaged leaves after harvesting. Use only whole leaves with a healthy appearance.