It’s only natural that the Alabama Cooperative Extension System can offer your maintenance crews expert advice on pruning hydrangeas. Popular in landscapes far and wide, the bushes are abundant in the South.
Administered through both Alabama A&M University and Auburn University, the extension maintains a wealth of horticultural information, including this publication on hydrangeas.
Alabama Extension researchers say many people – landscape workers among them presumably – are tempted to prune hydrangea bushes in February. Understanding flower development for each hydrangea species is helpful, Alabama Extension writer Katie Nichols reports, but February is not the time to prune them.
Some hydrangeas bloom on “old wood” while others bloom on “new wood,” the Alabama Extension says. Blooms on old wood are produced by buds set last summer. Flower buds forming on this year’s growth appear on new wood.
Alabama Cooperative Extension System Home Grounds team leader Kerry Smith says it’s best to prune shrubs that bloom on old wood shortly after current flowering to avoid removing next year’s developing buds.
“The next year’s flower buds begin forming in August,” Smith said. “If a shrub blooms on new wood, prune in late winter or in spring to stimulate new growth for additional blooms.”
Annual, general maintenance on bigleaf and oakleaf hydrangeas is recommended.
Remove all dead wood and cut about one-quarter to one-third of the older stems to the ground. This improves plant vigor, overall shape and bloom volume.
Smith said using July 4 as the last date for pruning these two species is an easy way to remember it.
Bigleaf and oakleaf bloom on old wood. A few bigleaf hydrangeas such as Endless Summer bloom on both old and new wood. Alabama Extension specialists advise choosing this variety, Nichols writes, if you live in an area prone to late frosts.
Both smooth and panicle hydrangeas bloom on new wood. Cut smooth hydrangea 6 to 12 inches from the ground, or at half its height, every year in late winter or early spring. The height for pruning these is strictly personal preference. Prune after initial flowering to stimulate a second flower flush.
Panicle hydrangea, sometimes called PeeGee, is most effective in tree form. Remove lower suckers and up to one-half of older stems for greater flowering.
Hydrangea hardiness, cold damage
The bigleaf hydrangea is the most cold-sensitive species.
It suffers with early or late freezes because the flower buds have a weak dormancy.
Surprise warm weather in winter or early spring causes the buds to emerge from dormancy, grow and become more susceptible to freeze damage.
Smith said the remedy is careful site and cultivar selection.
“If this type of weather is common in your landscape, plant bigleaf hydrangea on northern and eastern slopes under tall pines to reduce the temperature fluctuations that cause early bud break,” she said.
Your company’s landscape designers can also choose resilient cultivars that either bloom later or produce new buds for the current season.