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.
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
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. There are two varieties in our area that bloom on new wood.
New Wood Bloomers
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.
The reason that climbing hydrangeas are pruned in summer is because the flowers are produced on the previous year's wood. If they are pruned earlier in spring, before flowering, the blooms for that year will be sacrificed.
Lay down 6–8 inches (15–20 cm) of mulch around the plant base. Hydrangeas require a thick layer of mulch to protect them properly throughout the winter. Scatter your mulch materials to cover the ground around the base of your plants. Make sure that the mulch is at least 6 inches (15 cm) high.
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.
Prune back stems to just above a fat bud — called a heading cut — in fall, late winter or spring. These plants have conical-shaped flower heads. I recommend leaving the dry, tan flower heads on the plant to provide some winter interest in your landscape, so I wait to prune these until late winter or spring.
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.
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.
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.
Hydrangeas do not require strict reqular pruning; simply keep them healthy by removing dead wood and they will grow and flower well.
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.
"Stop deadheading in the fall, when bigleaf hydrangeas produce their last flush of flowers, to enjoy the dried blooms throughout the winter," she says. "These can be removed to help produce healthy buds in the spring."
There are several different types of hydrangeas—bigleaf, panicle, smooth, oakleaf, mountain. All these types should be fertilized at least once a season in late winter or early spring, certainly by the time new growth begins to show around the base of the plant.
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.
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.
Removing Spent Blooms on Hydrangea
Since hydrangea blossoms are so big, deadheading a hydrangea makes a real difference in diverting energy to more important parts of the plant's growth. You should carry out this practice all through the blooming season to encourage new blossoms and keep your plant looking fresh.