Where, Oh Where Have my Hydrangeas Gone.....?
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---Pat in Huntingtown, Maryland
A. We'll take the pruning part first, because it seems like I can't give this warning out often enough: No perennial plant should ever be cut back in the fall—ever, ever, ever. It interferes with them going dormant for the winter, which could cause permanent harm. And fall pruning can accidentally remove lots of flowers-to-be from blooming plants.
Now, you're always going to get a bad result when you prune Spring blooming plants, like azaleas, rhododendrons, and forsythia in the Fall. These early bloomers have produced all of their flower buds for the following year by mid to late summer, and people who 'clean them up' in the fall remove those buds and wind up with few to no flowers in the Spring.
But hydrangeas bloom in the summer, right?
Right. And most other summer bloomers—like crepe myrtle and butterfly bush—do best if they get a nice pruning in the Spring, about a week or two after all risk of frost is gone. But most hydrangeas bloom on what's called 'old wood'—growth from previous years, and not the current season. So when people prune their hydrangeas in the Fall or in the Spring, they're inadvertently removing the old wood that was poised to produce summertime flowers.
Now, I have to admit that the temptation to prune is pretty strong. Hydrangeas don't look very nice in the winter. And they look even worse in the Spring! The old branches look dead at the end of winter (even though they're almost always just dormant); and they are unattractive for a while. But the people who resist temptation and leave them alone will absolutely have the most flowers that summer.
Which begs the question: Can you ever prune them?
Yes, and it's one of my favorite cheap and sleazy gardening techniques. You leave them alone until all the flowers have formed early in the Summer, and then you go in and remove all the barren, non-flowering branches that are hiding the blooms from view. It's a great trick that makes the plants look like they have twice as many flowers, and there's no risk of harming future displays.
Now, to actually answer the question: Did these hydrangeas fail to bloom because of the fall pruning? The answer is a qualified use of the weasel-word maybe—because Nature has to share at least some of the blame. Lack of flowers is the rule this year in the mid-Atlantic, Northeast and other regions that experienced the crippling 'once-in-every-twenty-year' winter we barely survived, and not the exception. I repeat: It isn't you (this time, anyway); few to no hydrangeas are blooming in those regions this summer. Boo-hoo! Mean Mother Nature!
I know this for a fact, because we have gotten lots of emails about the problem—and similar sad queries about crepe myrtle and fig trees. The emails fall into three categories:
1)    The plants are stone cold dead; no sign of green growth late in the season.
2)    The top parts are completely dead, but there is some green growth coming out of the ground. And:
3)    The first email we receive says "my hydrangeas or figs or whatever are dead". But when I email them back and ask if there's any green growth at the bottom, they say 'yes'. So apparently I thought I knew what the word 'dead' meant, but I was wrong.
At any rate, the vast majority of hydrangeas in especially-harsh winter areas were slow to do anything this Spring, and then finally, some green growth appeared at the base. That's what happened to mine, and from all the emails I've gotten, it seems like my plants were poster children for this season.
So In June, when we saw the new growth that reassured us that the plants themselves were still alive, 'we' (which means my ace intern/helper/hired man Matt, who did all my chores while I recovered from rotator cuff surgery) carefully pruned back the old growth by just a few inches to see if that would stimulate the old branches into doing something.
We waited a couple of weeks, and when nothing sprouted, we removed all of the old branches that were crispy, snappy dead. Then we finally cut the rest of the old sticks back so we could enjoy this year's new growth—which is very lush and full; the plants are exactly the height they should be.
But no flowers. Not a one. Zip; nada; bupkiss. I do miss those big flowers, but I'm happy that the plants themselves are lush and healthy—and they don't look bad just as foliage plants. They're actually very attractive in full leaf—and a heck of a lot better than the dead sticks of May.
So, to all those whose hydrangeas are in the same place: Enjoy the lush greenery that reveals that the root systems survived; and don't you dare prune them until the flowers form—hopefully—next summer. Because the new growth you have now will be the only old wood the plant will have to produce flowers on NEXT year.
And if your hydrangeas—or other perennials—are really, most sincerely dead, I would urge you to replace them without worry. Those kind of winters should continue to be rare.