Lawn & Garden
AUBURN UNIVERSITY, Ala.—With every rule, there is an exception—such is the case with pruning hydrangea bushes, according to Bethany O’Rear, a regional home grounds agent with the Alabama Cooperative Extension System.
“Typically, for blooming plants a gardener follows the ‘May Rule,’” O’Rear said. “This rule dictates pruning time based on when a particular plant sets its flower buds.”
Old Wood and New Wood
Some plants flower on “old wood,” meaning blooms are set on stems produced from last year’s buds. These plants are usually the ones blooming during early spring. Since these plants bloom before May 1, prune immediately after blooms fade or finish.
Other plants set buds on this year’s growth, also called “new wood.” If flowering occurs after May 1, prune plants during the dormant season, in late winter or early spring.
“Following this general rule with hydrangeas would lead to a bloomless plant and an unhappy gardener,” O’Rear said.
The correct timing for pruning hydrangeas depends on the particular species of hydrangea. O’Rear says you must first identify the type of hydrangea growing in your garden.
“One of the most common garden varieties is the mophead or French hydrangea (Hydrangea macrophylla),” O’Rear said. “This is the type with either blue or pink flowers—depending on the soil pH.”
Mophead hydrangeas typically bloom early- to mid-summer. If gardeners followed the May Rule according to timing, these hydrangeas would fall into the dormant season pruning category. However, that is not the case. Mophead hydrangeas bloom on old wood and should be pruned soon after flowering.
“Another type of hydrangea that blooms on old wood is one of our native species, the Oakleaf hydrangea (Hydrangea quercifolia),” she said. “Pruning should take place just after the blooms have faded. In other words, these two types of hydrangeas are probably due for pruning right about now.”
Take care to put away the pruners by the beginning of August when next year’s buds begin to form.
The Peegee or panicle hydrangea (Hydrangea paniculata) blooms on new wood. This species can be cut six to 12 in. above the ground—or at half its height—every year in late winter or early spring.
“When it comes to pruning, correct timing is key,” O’Rear said.
Find more information about pruning, as well as site selection, bloom color, watering, fertility and cultivars in ANR-1276, Hydrangeas.