Hydrangea paniculata blooms late in summer on brand new wood. It's a fast growing big shrub, 8- to 10 feet tall.
Unfortunately, it's a bigger shrub than most people realize and so it's often planted in too small a space. (There are new "dwarf" varieties and we'll believe the size given on their labels just as soon as we see them stop growing!) Fortunately, with one simple pruning each spring any panicle hydrangea can be kept at half size.
You can cut a panicle hydrangea however you like, even right to the ground, during a winter thaw or early in spring. That year it will grow 3-, 4 or 5 feet and bloom on schedule. Or you can train it to a single trunk, call it a small tree, and cut the branches back to the top of the main trunk every spring. Either way the result is a plant that's smaller than it would be otherwise that is also full of lively new wood each year.
Here are some we cut each year because they can't be allowed to grow on to full size where they're placed. We cut them hard in early spring. The pictures tell the tale.
This particular tree hydrangea is not a great example of its species' form. Its canopy is unnaturally narrow as a result of crowding. The plant is in shade most of the day when it should have at least four hours of sun. It's also recovering from two years of even worse conditions while on hold in another area as utility construction took place in this area.
Yet it is a great example of the species' durable nature. Despite all, it still responds vigorously to pruning. What a trooper!
These shrubs had been pruned indiscriminately for about ten years before these pictures were taken. During that time they were simply sheared each time they seemed to be getting too big, sometimes several times in one year. This prevented some of the bloom, as branches cut in summer did not have enough growing time to produce flowers from their tips.
Additionally, branches at the base of the shrubs had been allowed to grow that crossed and inhibited each others' growth. In the photos below the shrubs are being pruned for the third time after that mistreatment. It's the final step of renovation -- removing 1/3 of the oldest wood each spring. It's also exactly what we'll do each spring from now on!
With Janet on this project you're seeing Chris Mahairas, an arborist with an interest in shrub pruning. He told us as we worked that he's especially fond of panicle hydrangeas. "There are so many of these in western Massachusetts where I grew up, I pretty much put myself through college on what I earned cutting and selling the flowers each summer."