Well, it turns out that I’ve been pruning my hydrangeas wrong this whole time. Not my bigleafs (Hydrangea macrophylla)—I have only a couple of those left in my beds, since they’re just not built for the late frosts in my region. I know to leave those babies untouched if I want a chance of any blooms. No, I’m talking about my smooth hydrangeas (H. arborescens).
Yes—the easy ones! The ones that bloom on new wood and every textbook tells you to cut back annually to keep them healthy and compact. I’ve been following that advice for years, and I’m betting maybe you have too. But that’s not what we should be doing.
Check out the article by Sam Hoadley, and the sidebar on pruning about midway through. As part of its native hydrangea trial, the Mt. Cuba Center in Delaware decided to see if there were any long-term benefits or drawbacks to performing heavy spring cutbacks on these shrubs. For three consecutive years, one example of each hydrangea in the trial was cut back to about 6 to 8 inches above the ground, while others were left completely alone. The result? (Caution: Spoiler alert ahead.) “After three years of heavy annual cutbacks, we started to notice a little burnout, typified by lower flower production in the cutback plants,” writes Hoadley. On top of that, the annual pruning did not help curb the floppy habits of the smooth hydrangeas.
Based on these observations, Mt. Cuba Center recommends against heavy annual pruning—contrary to traditional gardening practice. My. Mind. Is. Blown. Maybe you are like me and find pruning to be one of the most complicated landscape practices to grasp firmly. The timing, the technique—it’s all so precise. Mostly, I’m petrified of doing it wrong and harming my woody plants so badly that they never recover.
Case in point: I have a Koreanspice viburnum (Viburnum carlesii) that for years was growing wildly in every direction. I knew I needed to prune it, and to do so after it bloomed so that I didn’t sacrifice any flowers the following spring. But the maze of crossing branches paralyzed me from touching my saw for years—until I finally had enough, went rogue, and delivered a hack job so terrible that my precious viburnum looks like a classic “what not to do” photo in the book Crimes Against Horticulture. If only I had waited a year to read Jen Kettell’s comprehensive article on pruning viburnums in this issue. Hindsight is 20/20.
At least this upcoming season I’ll have more time to research proper pruning techniques, because I certainly won’t be wasting any time cutting back my smooth hydrangeas.
—Danielle Sherry, executive editor