When to prune hydrangea depends on the type of hydrangea. If you don’t know what variety you have there are tips that can help you figure out what plant you have.
Hydrangea generally bloom on either old or new wood, some newer varieties of bigleaf hydrangea (Hydrangea macrophylla) can bloom on both.
“Old wood” means the flowers in the spring were formed from buds that developed in the summer and fall before on last year’s stems. Prune these shrubs before August 1.
“New wood” means the buds develop on the current season stems. Prune new wood shrubs in late winter to early spring.
If you prune the hydrangea at the wrong time, you may cut off all the buds and not have any flowers during the growing seasons.
Bigleaf hydrangea, (Hydrangea macrophylla) are very popular and have been around a long time. This variety has large flower clusters that range in color from pink to blue to purple. The color changes depending on the soil pH. The buds form on last year’s wood. As a general rule, don’t prune after August 1. If you enjoy the dried flowers into winter, just prune around them.
Oakleaf hydrangea, (Hydrangea quercifolia) is a native shrub and known for the very large leaves that resemble leaves of an oak tree. The blooms are white to pink. They bloom on old wood so prune after the flowers are spent - late summer. The flowers are elongated, cone-shaped clusters, and sometimes used in dried flower arrangements. The winter bark can be a reddish in winter providing seasonal color. Same as bigleaf, the dried flowers are often enjoyed into winter, providing interest. Old canes can be removed to the ground rather than pruning or prune around the flowers you want to keep.
Smooth Hydrangea, (Hydrangea arborescens) or wild hydrangea is another native, it has a white flat, lace leaf flower, some varieties have a white ball type flower like the bigleaf. Bees are very attracted to the bloom. The soil pH does not affect the color. If you have a white variety, it will stay white. Smooth hydrangea bloom on new wood. It can be pruned back in late winter.
Panicle Hydrangea (Hydrangea paniculata) is the only hydrangea that can be pruned into a tree. If left as a shrub, it can form a large bush. The flowers are six to eight-inch-long panicles, the cream-colored flowers gradually fade over time to purplish pink. They bloom on new wood.
Researching hydrangea will help in identifying what type you have. Also, some trial and error with pruning may help. If you need help determining what hydrangea you have, contact me and we can figure it out together.
Kathi Mecham is a Horticulture Specialist for the University of Missouri Extension. Have a horticulture question you’d like addressed in a future column? Kathi Mecham enjoys hearing from readers and looks forward to sharing timely tips each month in Horticulture Hot Topics. You can reach her at mechamk@missouri.edu or call 660‑542‑1792.
