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How to Prune Your Hydrangeas
How to prune your hydrangeas generally depends on which of the four groups it falls in: Smooth, Panicle, Bigleaf, and Oakleaf. We cover other pruning methods in Pruning & Your Plants; however, this specific article aims to help you identify which type of hydrangea you have and its pruning needs. You may have recently purchased and newly installed a hydrangea, or yours may already be mature. Either way, pruning your hydrangea is a yearly occurrence.
Know your plant, know your pruning, and blooming can be a breeze!
Smooth Hydrangea
Hydrangea arborescens
Cultivar Examples: Annabelle, Snowhill
Note: Flowers on new wood
When: Dormant season (no leaves); annually
How: Cut all stems down to 6-12" tall
Smooth Hydrangea has smooth bark, thin leaves, and soft stems. This group includes the Snowhill and tried-and-true Annabelle cultivars (you know, those ones with the massive white mopheads). Smooth Hydrangeas are a breeze to care for - when the plants have gone dormant, take a hedge trimmer or pruner and cut all the stems down to between 6” and 12” in height. Do not prune them during the growing season or you will remove the flower buds and may miss out on the flower show. But what if you don’t prune them? You won’t hurt the plant, but it may look leggier and have fewer blooms.
Panicle Hydrangea
Hydrangea paniculata
Cultivar Examples: Tardiva, (Little) Quick Fire®, (Little) Limelight®, Vanilla Strawberry™, Strawberry Sundae®, Diamond Rouge™, Bobo®
Note: Flowers on new wood
When: Dormant season (no leaves); annually
How: Cut last year’s growth back to a point between buds by 1/3 to 2/3
Panicle Hydrangeas have woodier stems than Bigleaf and Smooth Hydrangeas. They typically have flowers that emerge white and turn to some shade of pink to red as the season progresses. Like their botanical name, the flowers are arranged in panicles and are generally more cone-shaped than round. Tougher than other species, they tolerate our soils well and seem to handle drought better than Smooth or Bigleaf selections. However, their stems do not resprout from the crown so you absolutely CANNOT use Rejuvenation Pruning on these plants.
Instead, you will prune them back to a point 1/3 to 2/3 of the way back on last year’s growth. Because Panicle Hydrangeas are oppositely branched, each cut will create two new branches below next year. If you want to keep your plant denser and more compact, you should prune them back to one or two buds above the start of last year’s growth. If you want the plant to be larger, then make more conservative cuts and only remove the last year’s flowers*.
*Note: if you have a hydrangea ‘tree’, then you should make more aggressive cuts and only leave one or two buds below your pruning cut. This is because the weight of new growth can snap branches and ruin the aesthetic of your hydrangea tree.
Zannah Crowe, Educational Horticulturist, Johnson's Gardens
"Hydrangeas are versatile and popular landscape shrubs that perplex many gardeners – there seem to be so many types, each with different light, pruning, and soil requirements. Without question, the most reliable performers for our climate are the Smooth Hydrangeas and the Panicle Hydrangeas. Both of these can be counted on to bloom magnificently every year, despite our frigid winters. Correct pruning is critical to achieving the beautiful blooms for which Hydrangeas are famous."
Bigleaf Hydrangea
Hydrangea macrophylla
Cultivar Examples: Endless Summer™, Bloomstruck®, Twist-n-Shout™, Cherry Explosion, Grateful Red®, Summer Crush
Note: Flowers on old wood
When: Dormant season or early spring; annually
How: Cut stems down to 6” stubs in winter. Or, cut back the plant to an even height and remove dead wood once the shrub begins to flush out in spring if a larger size is desired.
Bigleaf Hydrangea is a fancy species that usually comes with blue/purple and pink/red flowers that depend on soil pH to determine their bloom color. As their name suggests, this species has a large, thick leaf compared to other species. They also have stout stems that are more herbaceous than woody. In our region, the Bigleaf Hydrangeas tend to die back to the ground each winter and resprout from the crown in spring. Normally this means that they would never bloom, but the cultivars we carry are remontant, meaning that they can flower more than once per year. If you want to try your luck at having blooms on old growth, you can leave much of the plant up over winter. However, you will likely need to do some cleanup in spring to remove the deadwood on the plant. The easier method is to cut the plant down to 6” stubs (like Smooth Hydrangea) in fall/winter and let the new growth cover the deadwood once it’s flushed out.
*Note: the Bigleaf Hydrangea cultivars are notorious for randomly losing the ability to flower. In these cases, I have yet to find a good solution aside from either removing and replanting or accepting that you now have a lush foundation shrub that contrasts nicely with finer-textured plants.
Oakleaf Hydrangea – Hydrangea quercifolia
Hydrangea quercifolia
Cultivar Examples: Pee Wee, Jetstream™, Ruby Slippers, Snow Queen
Note: Flowers on old wood
When: After blooms fade (before the plant sets flower buds for next year); annually
How: Cut the plant back by 1/3 if size reduction is desired
Oakleaf Hydrangea is characterized by its cinnamon-colored exfoliating bark, large, lobed leaves resembling that of an Oak, and beautiful red fall color. This species is hardy to Zone 5, so you can expect some dieback in harsher winters. Oakleaf Hydrangeas flower on old wood and their flower buds are set at the tips of the branches. If you prune off the tips (terminals) in fall, then you will have removed all of your flower buds for the following spring. However, even if you do everything right, our Wisconsin winters may lay waste to your plant(s). Oakleaf Hydrangeas that are planted in more exposed areas or experience more extreme winter temperatures can lose their flower buds. The good news is that you still get to enjoy the lovely colored bark and beautiful fall color.
