A Fine Vine
The climbing hydrangea (H. anomala subsp. petiolaris, Zones 4-9) is a fabulous choice where you want to cover a large tree trunk or decorate a wall. The vine, left unpruned, can reach up to 50 feet or more. Its aerial roots cling to craggy surfaces such as the furrows in the bark of a tree. Grown freestanding, it becomes a hulking, shrublike form. White lacecap blooms garnish the plant in summer.
The climbing hydrangea also works well trained against a wall; or, to make the background surface easier to repaint, you can provide the plant with a sturdy trellis. As an espalier, the climbing hydrangea adds a formal dimension to your garden, and the structure of its winter branches—in addition to its exfoliating bark—offers as much ornament out of flower as in. I've seen a climbing hydrangea growing happily in the Pacific Northwest on a wall 8 feet long and 6 feet high for more than 10 years. The climbing hydrangea also fares well in Maine, especially along the coast, reports the University of Maine's Lois Berg Stack.
In the coldest climates (which includes Zones 3a through 5b), grow the hardiest of hydrangeas, H. arborescens and H. paniculata, says Stack. The oakleaf and bigleaf types are generally too tender to survive frigid winters.
H. arborescens blooms on new growth—wood that develops in spring. This makes it an easy choice in cold climates because blooms aren't formed on old wood—wood that developed the previous year—which may die back during the winter. Gardeners that prefer not to worry about when and how much to prune also find this shrub easy to care for. H. arborescens can be cut back in late winter to early spring (before new growth begins) and still produce lovely white flower clusters in summer. The cultivar 'Annabelle' bears immense heads of sterile flowers.
If you really love the bigleaf types but you live where winters are rough, a new introduction may be just what you are looking for. 'Endless Summer' has survived winter in Minnesota and come back to bloom in vivid pink the following season. A combination of traits makes this plant a winner in the north. Unlike most bigleaf hydrangeas, it blooms on both old wood and new, and it survives Zone 4 winters. "People are quite excited about 'Endless Summer'," says Stack.
Of course, no matter where you live, it's easy to get excited about hydrangeas, because they require so little from us and give back so much!
Pruning for Blooming
No blooms on your bigleaf hydrangea this year? Improper pruning may be the cause. But never fear: Pruning a hydrangea the right way is easy if you follow these guidelines.
Keep some of this year's growth. Gardeners often inadvertently cut off next year's flowers because Hydrangea macrophylla flower buds tend to form at the tips of branches and on old wood, meaning that the buds for next year's blooms form on this season's growth.
Remove one-third of the shrub's stems. Each year, keep the shrub less dense and rejuvenate it by removing up to one-third of the stems as close to the ground as you can, beginning with the oldest growth. Do this after the shrub has finished blooming; the remaining stems will bloom with bigger flowers than you had before when the shrub was crowded with branches.
Prune after bloom. Remove old flowers by cutting to just above the swollen buds for next year. And remember to cut off only the dried flower head, no further down.