Cut the dead stumps down to their base to completely remove them. This will allow the new growth underneath to have a chance to succeed. Dead and old blooms need to be removed to make room for new buds to come through. Cut the flower head off right above the first few leaves to encourage blooms for the next summer.
Hydrangeas that bloom on new wood can be safely pruned in late fall once the plants have gone dormant or in early spring. Next year's flower buds won't be formed until late spring the same year they bloom, so there is no risk of removing the buds if you prune in fall or spring.
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.
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.
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.
Mulch Matters
Weird winters with little snowfall and drastic temperature swings are detrimental to plants. To give hydrangeas their best chance at success, apply a layer of chunky mulch around the base of the plant. Decorative mulch is helpful but we recommend straw, marsh hay, or fallen leaves.
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.
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.
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.
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.
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.
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.
Mophead hydrangeas look lovely in the fall when their blue, purple and pink flowers contrast with the fall foliage. Brown flowers can be snipped off if they annoy you, but you don't have to remove them.
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.
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.
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.
Look at the foliage to identify your type of hydrangea. Mountain hydrangea foliage has serrated edges that are often tinted maroon at the edges. The round hydrangea flower form comes in what is called a mophead or lacecap version. The lacecap flower has outer petals that surround the pollen capsules in the center.