Warning: Giant Fleeceflower May Sucker

Highly promoted by Dutch plant whiz Piet Oudolf, a leader in the New Perennial Movement, the giant fleeceflower (Persicaria polymorpha) first appeared in North American nurseries in the early 2000s and has quickly become one of the most popular perennials.

This giant plant (it can exceed 8 feet/2.5 m in height under some circumstances!) bearing large creamy white feathery plumes is now found in many home and public gardens. It has proven easy to grow, very hardy (zone 3), extremely weed resistant and very long-blooming (it literally blooms all summer and into fall). It truly is an extraordinary plant and is, in fact, remains my favorite perennial. You’ll find more information about it here: Growing Giant Fleeceflower.

However, while the giant fleeceflower has always been presented as a totally no-care plant, with no flaws whatsoever, it has recently begun revealing a dirty little secret. Mature plants, after staying exactly where they were planted for a decade or more, have begun to show they have a hidden suckering habit. This completely contradicts what gardeners are being told. Every nursery I’ve looked into says it stays put, that it never suckers. But it’s becoming apparent that this is not entirely true.

Mature Plants Seem to Sucker

I planted mine 12 years ago, just as it was coming onto the market, and thus have probably been growing longer than most other gardeners. It has truly been a star and I proudly showed it off to all visitors. At first, no one had ever seen one, so they were suitably impressed. Now I find most serious gardeners do know it, but still, it remains an impressive plant.

After 11 years of growing as a single clump, though, two summers ago mine suddenly produced three suckers. Not spindly little things, but big well-rooted clumps. And up to 3 feet (1 m) from the mother plant, at that. I’ll admit, this doesn’t even come close to the running stolons of the other fleeceflower relatives, the knotweeds (plants in the genera Persicaria, Polygonum and Fallopia), but still, it was a shock. After all, I’ll been promised it would never spread.

But it only seemed to have happened to me. No one else ever mentioned it. Until this summer. One of my blog followers reported “many” (no number was given) offshoots appearing all around his mature giant fleeceflower. He wanted to know what had happened. And so did I.

Seeking Information

I just got back from the 2016 Perennial Plant Conference  held at Swarthmore College, Swarthmore, Pennsylvania, where I presented a lecture on shade perennials. No less than three of the six speakers mentioned giant fleeceflower (P. polymorpha) in their presentation and all highly recommended it. None mentioned it suckering. I checked with all three after their talk and no, none had ever heard of giant fleeceflower spreading. Of course, the room was full of perennial experts and I quizzed quite a few of them. Likewise, no one had ever heard of that happening. One suggested I had bought the highly invasive and similar-looking Weyrich’s knotweed (P. weyrichii) by mistake, but I’ve grown that plant (and never will again: what a weed!) and mine was definitely P. polymorpha.

But then I talked to Cassian Schmidt, Director of the Hermannshoff Garden in Weinstein, Germany, also a speaker, and he confirmed to me that German gardeners, who have been growing giant fleeceflower for a longer time than North American gardeners, are becoming increasing concerned about its late-in-life weedy habit. I would have liked to have known if there was some specific combination of conditions, besides the plant reaching 10 years or so in age, that would provoke this sudden bout of suckering, but he wasn’t aware of any.

The Plant’s Real Name

Cassian Schmidt also informed me that Persicaria polymorpha is probably not the right name for this plant. It is apparently a natural hybrid, likely between P. alpina and P. weyrichii, that was found in Finland, and, according to him, its real name is P. x fennica or even Aconogonum x fennicum (depending on whether you’re a lumper or a splitter). He pointed out that flowers of giant fleeceflower are sterile, which would be very unusual in a true species, but common in an interspecies hybrid, because hybrid plants are often unable to produce viable seeds.

Please note I’m not trying to push for a name change (we’re only just beginning to know the plant under the name P. polymorpha and changes in botanical names cause so much confusion), but I figured I ought to let you know…

Forewarned is Forearmed

And there you go. You are now aware of giant fleeceflower’s dirty little secret: it sometimes does sucker, especially when it reaches a certain age. Of course, no one seems to know yet if this is a widespread problem or one that will be limited to certain environments. Still, at least you know about this flaw and, in gardening as in other fields, forewarned is forearmed!