How to Prune Mophead Hydrangeas

Shakespeare was thinking of weightier matters when he wrote about "the most unkindest cut of all," but it wouldn't hurt to recall the phrase before taking a pruner to your mopheads in spring. Beautiful mophead hydrangeas (Hydrangea macrophylla) need but little pruning, and almost all of it should happen months earlier than spring.

Mophead hydrangea blossom clusters look like colored snowballs, and, as far as a garden goes, the more the merrier. Yet even mopheads can profit from regular pruning. Before sterilizing that pruner by wiping it with a rag soaked in denatured alcohol, figure out your pruning goals. It's always a good idea to remove dead and diseased wood, and some gardeners like to refresh the plant or control size by removing a number of stems annually. Mopheads thrive in U.S. Department of Agriculture plant hardiness zones 6 through 9.

Prune mopheads just after the plant flowers in mid-July or August, when blossoms fade and healthy shoots develop from the lower stems. Mopheads set their buds on old wood, which means that by October, when you prune the shrub you'll be pruning off buds. The late-summer-pruning rule applies to all summer-blooming cultivars, such as "Glowing Embers" (Hydrangea macrophylla "Glowing Embers"), hardy in USDA plant hardiness zones 7 through 9. It's not the case for mophead cultivars that bloom both in spring and summer, like Endless Summer (Hydrangea macrophylla "Bailmer"), which grows in zones 4 through 9. It buds on old and new wood, so you can prune it in fall, winter or early spring.

If they're planted with ample elbow room, mopheads do not necessarily require pruning to remain healthy and vibrant. On the other hand, annual pruning can produce bigger flowers, a denser shrub and a shorter one. First, prune out any dead, damaged or crossing limbs at ground level or to a healthy bud. Then remove at ground level the longest, oldest stems, removing up to one-third of the older live stems. Alternatively, reduce the length of the longest stems as desired, cutting each back to healthy buds.

Deadheading describes the practice of clipping off faded blooms, generally during the growing season. It's a way of cleaning up the shrub, making it look fresh, and encouraging new blooms to grow from lower forming buds. After sterilizing the pruners, clip off the faded blossoms just above the buds forming on the stems below the blooms. You can deadhead mopheads in late summer or early spring, because removing dead blossoms does not eliminate buds.