By Julie Weisenhorn, UMN Extension educator, horticulture
Hydrangeas are one of the most popular blooming woody shrubs in Minnesota landscapes and, as you’d expect, people often ask how and when to prune these beloved shrubs.
Hydrangea paniculata, panicle hydrangea
Prune back stems to just above a fat bud — called a heading cut — in fall, late winter or spring. These plants have conical-shaped flower heads. I recommend leaving the dry, tan flower heads on the plant to provide some winter interest in your landscape, so I wait to prune these until late winter or spring. Some favorite panicle hydrangeas:
- Quick Fire® (H. paniculata ‘Bulk’ PP16, 812)
- Limelight (H. paniculata ‘Limelight’)
- First Editions® Berry White® (H. paniculata ‘Renba’ PP28, 509)
Hydrangea macrophylla, big leaf hydrangea
These plants produce buds in late summer to early fall (August-September) that will form next year’s flowers. So prune these shrubs after they finish blooming before August (again, make a heading cut).
An exception is the Endless Summer® The Original Bigleaf Hydrangea (H. macrophylla 'Bailmer' PP15,298) and other cultivars in the Endless Summer series from Bailey Nurseries such as Blushing Bride, BloomStruck® , Summer Crush®, and Twist ‘n’ Shout®.
The H. macrophylla bloom on last year’s wood and new wood that grows this year. So it will bloom whether you prune it or not. Protect H. macrophylla in winter from rabbit browsing on the stems with a large, 4-foot tall ring of hardware cloth.
The Endless Summer hydrangea made a huge splash on the Minnesota landscape plant scene because of its pink to blue color flowers (achievable with proper soil amendment) and because it blooms on old and new wood.
Hydrangea arborescens, smooth hydrangea
Let these plants grow a season or two before doing any serious "hard" pruning. Once the shrub is established and has a couple of growing seasons under its belt, prune these hydrangeas in the spring down to the ground, or not at all if you want a larger shrub. Flower buds will grow on this season’s growth or new wood.
Some favorite smooth hydrangeas:
- Invincibelle Mini Mauvette® (H. arborescens 'NCHA7' PP30,358)
- Incrediball® (H. arborescens 'Abetwo' PP20571)
- Annabelle (H. arborescens 'Annabelle')
Hydrangea petolaris or climbing hydrangea
This tough, gnarly vine needs little to no pruning ever, except for removing any dead wood that develops.
Plant this vine in full sun on a solid trellis or fence where you want a long-living, dense screen. It is a dickens to get rid of once it gets established.