The rise in popularity of panicle hydrangeas (Hydrangea paniculata, Zones 3–8) has been staggering over the last fifteen years. This rise is due in part to several new cultivars entering the market. Additionally, people are realizing how little care these hydrangeas really need. Most gardeners I know with an ounce of sun in their garden have at least one panicle hydrangea.
Traditional winter pruning
I love the high-summer blooms of panicle hydrangeas. For many of us in the Southeast, July is when we see peak bloom. This coincides with annual flowers really starting to strut their stuff. If July is when you want your hydrangeas to bloom in the Southeast, you should prune plants in late winter or early spring. Don’t be afraid to cut plants back hard. As long as you don’t lop them off at ground level and have several branches left, you’ll be fine.
However, there’s an alternative technique to pruning panicle hydrangeas that we can utilize in our region. Be warned—this is not for the faint of heart and may even contradict most of the advice you’ve heard. But rest assured that I’ve done this before with much success.
I am lucky enough to have several cultivars of panicle hydrangea in my garden. With some of them, I follow the standard advice and prune in late winter or early spring, and they bloom beautifully in mid-July. However, for many of those cultivars, I’ve decided I don’t want them to bloom in July—I want them to bloom in September, or maybe even a little in October. This is especially true for cultivars that have a pink or partially pink bloom. The cooler nights later in fall help bring out colors you would not see in July.
I accomplish this in my Zone 7 garden by cutting back the new growth sometime in early to mid-June. Pruning toward the beginning of June should also work for Zone 6. If you are in Zone 8, I suggest any time after June 1, but you may be able to go into early July as well.
My goal is to prune the shrubs right before they start to form substantial flower buds. Because they bloom on the current season’s growth, you will have plenty of time for them to form new buds. This in turn will give you a later season of bloom. With this technique, I don’t cut them back hard like I would in winter; instead, I just trim back the current season’s growth. You don’t want to do a hard prune in summer. These plants are relatively drought tolerant, but if you practice this technique, you will want to provide a little supplemental moisture during dry spells.
Added benefits of summer pruning
Why did I start doing this? The first reason was to get more blooms in my fall garden. The second reason was to see if I could enhance the color of several panicle hydrangeas that were advertised as having pink or partially pink blooms. In my Southeast garden, even panicle hydrangeas with “pink” in their cultivar name never turned pink for me. Although they may never look like the marketing photos in our region, the cooler nights in the fall do bring out variations in bloom color you would not see in July. I hope you consider this technique the next time it comes to pruning your panicles. You’ll never know until you try.
—Andy Pulte is a faculty member in the plant sciences department at the University of Tennessee.