A plant for the wildlife-friendly yard, "Red Rocks" penstemon (Penstemon x mexicali "Red Rocks") attracts hummingbirds, butterflies and bees with its red to pink bell-shaped flowers. Individual flowers sport white throats and grow along 3-foot-tall flower stalks. Growing in U.S. Department of Agriculture plant hardiness zones 4 through 9, this herbaceous perennial thrives in full sun and fast-draining soils. A "Red Rocks" penstemon benefits from periodic pruning throughout the growing season to maintain and improve its appearance and health.
Pinch the terminal end off of each stem of the "Red Rocks" penstemon in spring, once the stems reach 12 inches in height. Make each cut horizontally through the stem with a pair of bypass pruning shears, 1/4 inch above the second set of leaves located below the stem's tip. This process will encourage lateral branching, creating a bushier plant with more flowers.
Prune back dead, broken, yellowing or dry stems as they appear throughout the growing season. Cut the stem back to a growth node, bud or set of leaves 1 to 2 inches above ground level.
Deadhead the plant throughout the summer, removing flower stems as their colors fade and petals become limp and drop. Grasp the stalk in one hand and bend it gently to one side, exposing its base. Cut through the stem at a 45-degree angle with bypass pruners, 1/4 inch above a bud or set of leaves located 1 inch above ground level.
Trim any vigorously growing stems that appear leggy or grow outside of the penstemon's general shape after the summer blooming period finishes. Remove the top one-third of each wild stem, cutting it 1/4 inch above a set of leaves or side shoot.
Cut the entire plant back after the second fall blooming period ends. Cut off the top one-third, to one-half of each stem, 1/4 inch above a set of leaves or growth node.