Established plants (three to four years old) can be harvested in spring as the tender spears emerge. Cut or snap off the shoots just below the ground when they are 5 to 8 inches long. Cut carefully to avoid damaging the tips of nearby spears that have not yet emerged from the ground. Or snap off the spear by bending the stem towards the ground. Regular picking will give you fresh better tasting spears. Stop picking after 6 to 8 weeks. The stems will develop into a large airy plant. Leave the leaves intact throughout the season to produce needed energy for next year's harvest. The yellowed foliage can be cut back to the ground in fall or allowed to stand for winter to capture snow (in northern gardens) for added insulation.
Photo Courtesy Missouri Botanical Garden Plant Finder