Knowing when to prune your Hydrangeas can be the difference between a bush full of vibrant blooms and one with no flowers at all. But the right timing will depend on which variety you’re growing. The first and most important question is: do you have a Hydrangea that blooms on old or new wood?
Bigleaf varieties, including Mophead, Lacecap, and Mountain Hydrangeas, flower on old wood, and any pruning should be done in the summer. Oakleaf and Climbing Hydrangeas follow this pattern as well. Panicle and Smooth Hydrangeas bloom on new growth and are best pruned before the growing season gets underway.
Many gardeners experienced in the Way of the Hydrangea will tell you that sometimes the best approach is to prune nothing at all. Some old-growth Hydrangeas require no regular trimming other than dead-heading and should only be pruned back if you need to correct their size or shape.
The Difference Between Old and New Wood
If you haven’t spent a lot of time tending flowering shrubs, you might be wondering why the timing of your trimming would affect the plant’s blooms at all.
The reason is that some plants, much like garden bloggers writing on a deadline, thrive under pressure. They bloom later in the season, on the growth that’s been added to their branches since the previous year. Pruning them before the growing season releases hormones that let them know there’s work to be done.
We call these “new growth” or “new wood” bloomers, and if they’re not pruned regularly, they tend to become woody and slow down their flower production. They’ve settled down and don’t have anything to prove anymore, so they stop putting out the showy blooms that Hydrangea growers love.
Old wood bloomers are just the opposite – they’ll wait until they’re good and comfortable to produce flowers. When their branches grow, the new sections won’t produce any flowers until the following season.
Plants that flower on old growth tend to be lower-maintenance. You’re better off letting them go about their business undisturbed as much as possible. Any pruning beyond removing dead blossoms, and carefully thinning the branches here and there, will reduce the number of blooms you see next season.
You can generally tell what kind of plant you’re dealing with based on when the flowers appear. Because new wood plants have to grow back before they start producing blooms, they flower later in the growing season, starting in the middle of summer and often lasting into the fall.
On the other hand, if you have a shrub or tree that’s blooming before June, it’s a pretty safe bet that it’s an old wood bloomer.
If you’ve gotten this far and you realize that you’ve already pruned your Hydrangeas too much or too soon, don’t panic. Hydrangeas are fairly hardy and forgiving plants. You might have to deal with a season of less prolific flowering, but if you follow this guide, then they should be back in action the following year.
Which Hydrangeas Bloom On Old Wood?
Many of the most colorful Hydrangea varieties are old-growth bloomers, including:
Mophead Hydrangea. Perhaps the most popular Bigleaf variety. Beloved for its large, round flower clusters, often in bold blue, purple, or pink.
Lacecap Hydrangea. Produces clusters of delicate buds ringed by larger, flatter blossoms.
Mountain Hydrangea. An excellent choice for harsher climates. Its flowers resemble Lacecaps, with even smaller outer blossoms.
Oakleaf Hydrangea. Named for its distinctive tree-like leaves, which change colors in the fall. This variety accents its leaves with clusters of delicate white flowers.
Climbing Hydrangea. The vertical-height champ of the family. This variety loses its leaves in the fall, revealing a distinctive peeling bark.
How and When to Trim Hydrangeas That Bloom on Old Wood
Hydrangeas that flower on old wood require less pruning as a general rule. Unless you need to trim them back to preserve their shape or keep them from crowding out their neighbors, it’s best to let them do their thing.
Some gardeners do recommend pruning away a few of the oldest stems to keep the plant producing large flowers. The new stems that grow in won’t flower next season but will be vigorous bloomers after that.
If you’re taking this approach, cut the stems you’re removing all the way down to ground level. The usual rule of thumb is to take away about a third of the stems, focusing on the oldest ones or any that look particularly weak.
When you need to cut your shrub back to shape it or reduce its size, bear in mind that the stems you cut will likely not flower next season. A gradual approach in which you slowly downsize the plant over a few growing seasons can ensure that you still get some blooms in the meantime.
The right time for pruning Hydrangeas that flower on old growth is the height of summer, after the plant has finished flowering but before it’s begun to form new buds. Any later than July and you risk suppressing next year’s flowers.
The advice above only refers to trimming flowering stems. If the plant has dead or damaged stems after the winter, you can trim these, though you’ll still want to use a light touch. Cut back to just before the start of the damaged section.
Clearing away dead blossoms to keep your Hydrangea looking fresh is also fine. If you do this after July, you should cut just as close to the bloom as possible to avoid disturbing the developing buds.
Which Hydrangeas Grow on New Wood?
Two primary types of Hydrangeas produce their blooms on the season’s fresh growth:
Panicle Hydrangeas, which tend to produce rich conical flowerheads. They’re often quite cold-tolerant, especially the increasingly-popular Limelight variety.
Smooth Hydrangeas, like the well-known Anabelle, which tends to remain fairly compact despite being a new-growth variety.
How and When to Trim Hydrangeas That Bloom On New Wood
Unlike their more sedate cousins, you don’t want to tiptoe around these Hydrangeas. They should be cut back aggressively every season to keep them working hard. This will prompt them to produce the big flowery pom-poms that you know and love.
In theory, you can prune these varieties any time but summer. But the ideal window is late winter or early spring, before they’ve begun growing out.
Again, don’t hold back – trim the entire shrub at once. Many gardeners recommend cutting all the way to the base, leaving no more than six inches of stem poking out of the soil. You may want to leave a little more on there if you’re trying to increase the size of your Hydrangea.
Some growers contend that pruning all the way back to the soil can weaken Smooth Hydrangeas over time. If you’re worried about this possibility, you can go for a slightly longer cut and leave a couple of feet remaining aboveground.
A Note on Endless Summer Hydrangeas
Some enterprising Hydrangea breeders, tired of the limitations of old and new growth varieties, said, “Get you a plant that can do both!”
The result is known as the Endless Summer Hydrangea, which produces flowers on both new and old wood. This means that their blooms appear earlier and last longer than many other types.
Naturally, this has implications for proper pruning. An Endless Summer shrub shouldn’t be trimmed back to the base unless it’s so old or damaged that it needs a reset. In general, these Hydrangeas require very little pruning at all, except to clear away dead wood and blooms. If you must trim it, do so in the summer like you would with an old wood bloomer.
Final Thoughts
Timing is everything in gardening, and knowing when to trim your Hydrangeas is crucial to getting the best blooms possible. Smooth and Panicle Hydrangeas, which flower on new growth, are best trimmed in late winter or early spring. Cut the whole bush back near to the ground to stimulate the production of fresh stems.
Trim all other types of Hydrangeas in the summer, after their flowers fade. You should only remove dead wood and a few of the oldest or weakest stems.
Finally, don’t be afraid to experiment! Hydrangeas are remarkably tolerant, and in the long run, there’s no substitute for experience in the garden.