Cause of flopping hydrangeas remains a mystery

Last year at this time, I bemoaned the fact that my hydrangeas had completely flopped. As I fought off mosquito attacks, I worked into the night to stake each heavy flower on Hydrangea arborescens Incrediball, individually supporting it with twine led to a tall stake, the closest I’ve ever come to knitting.

I went to that extreme last year for a photoshoot of my garden and wrote off the flopping problem on a hydrangea that is said to have stiffer stems than the notoriously floppy ‘Annabelle’ as a rare occurrence due to last summer’s drought.

So when the Incrediball hydrangeas flopped spectacularly this year, after we’ve had plenty of rain, I made two decisions. The first was to let them lay and perhaps cut some flowers for an enormous bouquet, and the second was to get to the bottom of this flopping problem.

But that’s easier said than done.

I went through my mental checklist of everything that might cause flopping when it hadn’t been an issue for the first eight years of these plants’ lives in my garden.

The light exposure hadn’t changed over the years, so that was easy to rule out.

My fertilization schedule hadn’t changed either, but it was worth considering as over-fertilizing can lead to a lot of soft growth. When it comes to shrubs and perennials, I do very little fertilizing, only giving some organic fertilizer to particularly hungry plants, hydrangeas included. But my scant dose of a low-nitrogen rose fertilizer, chosen to promote flowers, not foliage, once a year in spring seemed unlikely to be the cause.

Pruning is a little different with Incrediball than with other H. arborescens, and the advice is to cut them back to about a third of their height in early spring. I’ve been playing around with pruning, trying out cutting some stems back to about 8 inches and others to 30 inches, and I can confirm that none of it made a difference. Every stem flopped equally as dramatically.

Having checked off everything on my “Why didn’t that plant do what it was supposed to” list with no clear answer, I reached out to Stacey Hirvela, a horticulturist and the marketing manager for Spring Meadow Nursery, which developed the Incrediball hydrangea, along with many other varieties.

She suggested that the rain that I thought might prevent the flopping may actually have caused it. Sometimes those big, basketball-sized flowers get so weighed down with water that the stems can’t recover.

But beyond that guess, she just didn’t know. “Like so many other things in horticulture, there’s no one answer,” she said.

All my sleuthing came down to that — we don’t really know.

Although it would have been nice to narrow down a cause, it doesn’t make much difference. There’s a good chance these Incrediball hydrangeas will be replaced. I don’t love the idea of facing another year of flopping and I don’t care to spend my time staking hydrangeas.

Because sometimes plants don’t do what they are supposed to and we just don’t know why.

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