Don't do it or you'll risk cutting off the flower buds. Pruning your hydrangeas to reduce their height isn't effective because they will grow right back to their original size, or even larger because the act of pruning stimulates new growth.
Wait until Spring to prune hydrangeas
While some plants bloom on new growth, others primarily set flower buds on old wood. Regardless, it is best to wait to prune all hydrangeas until spring. In the fall, hydrangeas (and all trees and shrubs) are in the process of going dormant.
"When to prune these woody-stemmed hydrangeas is not as critical as [with old wood] varieties, as long as you avoid pruning when the flower buds are opening," says Becker. Trim in early spring, before the flowers begin to bud, or after the plant has finished flowering.
If you prune them at the wrong time, you could risk cutting off all the flower buds and ending up with no blooms that year.
To rejuvenate the hydrangea, remove up to 1/3 of the older living stems down to the ground each summer. This will revitalize the plant. If necessary to control the size of the plant, cut back before late July to allow for buds to develop. Usually the plant will return immediately to its former size.
To reduce the size of a hydrangea that blooms on new wood, cut off about one-third of each stem in late fall or early spring before it begins to leaf out. If your hydrangea blooms on old wood, prune right after it has bloomed when the flowers are fading.
Wrap with winter protection.
During the winter, make a DIY A-frame wire cage out of burlap and chicken wire to protect your hydrangea plant. This cage will protect it from winter winds, heavy snowfall, and cold temperatures.
Cut back in early spring, pruning last year's growth back to a healthy framework that's between 30cm and 60cm high. Prune to just above a pair of healthy buds on each stem. Cut back to the lowest healthy buds for big flowers or less hard for a natural look or a taller plant.
Without going through the deadheading process, hydrangeas will not produce as many flowers and the few produced may not grow as big to their full potential.
According to Hirvela, your hydrangea is done blooming when the color of the flowers has faded in a non-appealing way. "There are a few varieties that will continue to push out new buds through late summer and autumn," she says.
But when to prune them? Prune fall blooming hydrangeas, or old wood bloomers, after they bloom in the summer. If you prune old wooded hydrangeas in fall, you are cutting off next seasons blooms. Summer blooming hydrangeas, or those that bloom on new wood, are pruned in the fall, after they stop blooming.
Bottom-line: Panicle-type hydrangeas should be pruned in late winter or early spring. While they could be pruned in fall, we highly advise waiting until late winter/early spring to reduce risk of injury.
In late winter or early spring, these shrubs can be cut all the way back to the ground. Smooth hydrangeas will produce much larger blooms if pruned hard like this each year, but many gardeners opt for smaller blooms on sturdier stems.
Keep Them Cozy. Whether or not hydrangeas need protection depends on how cold the winter temperatures drop. If the air temperature doesn't go below 0 degrees (zone 7) there is no need for winter protection. In colder climates, wrap or completely cover marginally hardy hydrangeas.
It's best to start adding coffee grounds to the soil months before the blooming season begins, ideally in the late fall. You can repeat the process with your typical fertilizing schedule. With a little caffeine and a lot of patience, your hydrangeas should reward your efforts come spring with the boldest blue globes.
Some gardeners report success in turning their hydrangeas blue by applying coffee grounds to the soil. The coffee grounds make the soil more acidic, allowing the hydrangea to more easily absorb aluminum.
Many customers ask why their hydrangeas aren't blooming. The primary reasons hydrangeas don't bloom are incorrect pruning, bud damage due to winter and/or early spring weather, location and too much fertilizer.