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.
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.
Prune back stems to just above a fat bud — called a heading cut — in fall, late winter or spring.
If you don't prune hydrangeas then they can eventually resemble a tangled mass of woody stems, and the flowers will become smaller and less showy.
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.
New Wood Bloomers
These are the hydrangeas that set flower buds on current season wood (new wood). It is easy to grow these hydrangeas because they bloom every year regardless of how they are cared for or treated. They can be pruned to the ground in the fall and they will emerge in the spring with bountiful blooms.
4. No need to prune. If you trim your plants in fall or winter, you may mistakenly remove flower buds for the following year on bigleaf and oakleaf hydrangeas. Leaving the old flower heads on the plants will also add some interest to the winter landscape.
When to prune hydrangeas. Most pruning is carried out in late winter or early spring. However, the climbing hydrangea is pruned after flowering in summer.
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.
Generally, it is safe to prune as much as one-third off of your hydrangea that blooms on new wood.
Regardless of the type of hydrangeas you're growing—and whether it blooms on old or new wood—the cutting process is the same. Start by using clean, sharp shears, then make your cut. "Cut stems above a node, and include at least two leaf groups on the cut stem," says Godshalk.
After a day or so of being cut, the blooms begin to wilt. About three days later, they are completely done. But guess what I just learned (from an instagram conversation)? Hydrangeas take in water from their PETALS!
So the bottom line is that if a hydrangea is too large for the location where it has been growing, the best thing would be to move it and plant a smaller variety in that spot.
To prepare hydrangeas for winter in colder areas, add a thick layer of mulch around the base of the plants to protect the crown and roots from freezing temperatures.
Hydrangeas that bloom on new wood require pruning in late winter or early spring. Prune to shape, cutting back to about two feet. The pruning promotes new, sturdy growth, which provides the blooms next season.
So these shrubs should be pruned immediately after their flowers fade. Conversely, if the shrub flowers on new wood (stems developed during the current season), its buds are set within the season, so the shrub should be pruned in early spring before that new growth emerges.
Cut back any clearly dead branches, which are brittle and snap off easily. This can be done in the fall or any time you see a dead branch. 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.
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. They do not produce very much new growth until the following spring.
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.