What is the best time to prune, how much to prune & should the bushes be dead headed?
Sussex County Delaware
Hello, thank you for your question! You did not mention what kind of hydrangea, and knowing which one is significant. In our area, there are four major types of hydrangea. I personally grow all of these types and have a total of 64 at my home. So I am a big fan!
- Macrophylla (big leaf) hydrangeas. This is what typically comes to mind when people think of hydrangeas. Also known as “hortensia” “mophead” or “French Hydrangeas” we see them typically in hues of blue and pink with new cultivars and colors introduced every year. These bloom on old wood, in our area USDA Zone 7a or 7b, in June. In the past couple of decades, a reblooming variety, such as the Endless Summer brand, have been bred to bloom on both old wood and new wood, thus extending their blooming season. The traditional old wood bloomers will age and change color, and it is a personal preference whether to leave the blooms on, or deadhead them. If they are old wood only bloomers, deadheading will not encourage new blooms. There is no right or wrong answer. However, be careful when deadheading not to cut down to the next set of leaves. Macrophyllas will set their blooms for next year by August or September, close to the axils where the leaf nodes are located. If these are removed, you will remove the blooms for next year. Unless you must cut down for size reasons (growing over a window) macrophyllas thrive without pruning. Reblooming macrophyllas will benefit from dead-heading the old blooms to encourage new blooms to emerge, though reblooming is seldom as vigorous as the initial blooms in June. Many people worry about bare canes. These should not be pruned back until later in the summer. Do not prune canes in the spring, or you will make those freshly-cut canes susceptible to hydrangea cane borer (evident by small holes at the top of the canes). Macrophyllas thrive in morning sun and afternoon shade. They transplant well, but expect a down year as they recover and adjust. Incorrect pruning or aggressive pruning of “macs” is the number one reason for failure to bloom. The second culprit to lack of blooms in this variety is a late spring frost.
- Quercifolia or Oakleaf hydrangeas. These are native to the eastern U.S. and can be pruned only if necessary and follow the same rules as macrophylla hydrangeas. The panicles are long and the leaves are heavily lobed and age beautifully in the fall. Most owner of Oakleaf hydrangeas simply leave them alone unless size becomes an issue.
- Paniculata/Panicle hydrangeas. These are typically white to lime white panicle or cone-shaped blossoms which eventually age, depending on the variety, to lime, green, pinks, reds and browns. They love sun! Panicles are known by names such as Limelight, Quick Fire, Bobo, Pinky Winky, Peegee, Vanilla Strawberry, etc. Some are bred to be dwarf sized. These hydrangeas bloom on new wood. If you want to control the size or the shape, or train as a tree, pruning can be done in early spring, e.g., March. You can cut panicle hydrangeas back by one to two thirds. Cutting back or removing straggly branches will affect the size of the blossoms. So, a heavy pruning will result in larger blossoms, but less of them. You don’t have to prune them at all, and the shrub will grow significantly on top of last year’s wood—blossoms will be plentiful, but slightly smaller in size compared to if you had pruned back hard.
- Arborescens or smooth hydrangeas are native to our region. Popular cultivars are Annabelle, and a sturdier cultivar known by the trade name Incrediball. They have a rounded leaf and a rounded, old-fashioned blossom. Follow the same pruning schedule/options as panicles. They bloom on new wood. Like panicles, they are typically white to greenish white, with some blush pink cultivars being introduced on the market. These hydrangeas are known to flop or weep, particularly after a heavy rain. If you desire sturdier branches and larger blossoms, prune back by a third to a half of its size in early spring. If you don’t prune, the Annabelles in particular will get larger in height, but the blossoms will be smaller and the shrub is likely to require some staking.