Many of the perennials I love are just a little too invasive for my taste. You plant them in a small corner of the flowerbed and the first thing you discover is that the whole flowerbed has been invaded, along with the neighbor’s lawn, vegetable garden, pathway and everything in between. It’s only fair that a perennial should grow in diameter every year. After all, it’s in their very nature to expand a little over time and, what’s more, the gardener has plenty of time to reduce the mass, to control its spread. However, producing rhizomes and stolons that run everywhere and take root as soon as they touch the ground is pure aggression!
Invasive plants…
How invasive can these plants be? I once planted a dotted loosestrife (Lysimachia punctata) in a flowerbed one year, only to find a stalk of the same plant four meters away, completely at the other end, the following season. Assuming it was a seedling that had become established, I pulled the plant out… only to discover a long rhizome running all the way back to the original plant! This is, of course, an exception, but it’s not uncommon to see an aggressive perennial monopolize up to a square yard of new bed space after just 12 months. That’s not just one square yard a year, because these plants scatter exponentially. If you don’t act fast enough, your flowerbed will be gone in just a few years!
Easily Handle These Plants
So I deal with the worst of these “octopus plants” easily. I don’t plant them! As for me, goutweed, macleaya and Japanese knotweed are good only for the garbage can. I’ll never plant them. I care too much about my little plot of land to want to see it eaten up by these unscrupulous aggressors. By the way, if you find one of these plants on your property, I’ve got a good solution for you: move!
On the other hand, some of these invasive perennials are less space-hungry and so pretty that I can’t help growing them. Bee balm (Monardia), yarrow (Achillea millefolium), lionshearts (Physostegia), dotted loosestrife (Lysimachia punctata), gooseneck loosestrife (Lysimachia clethroides), etc., all delight me. They do us too much good to eliminate them completely from the flowerbed. But I can’t allow them to invade and then drive out the other perennials, which are incapable of defending themselves against the onslaught. So I control them from the start by planting them inside a root barrier sunk deep into the soil, usually a recycled plastic bucket with the bottom removed. The expansion of their rhizomes is limited by such a barrier, there’s no danger of the plant escaping and peace returns to the flowerbed.
The Clash Of The Titans, A Revealing Trial
However, I wondered what would happen if I planted spreading perennials in a communal bed, with no barrier to prevent them from escaping. With each plant exhibiting roughly the same aggressive behavior, could I end up with a bed so well balanced that it required no, really no, maintenance? A perfect bed! So, several years ago, I tried the experiment on a piece of land that didn’t belong to me, a bit of disused cemetery (after all, I wasn’t foolish enough to carry out the experiment in my own garden!).
I dubbed the trial the “Clash of the Titans” and designed it rather like a professional wrestling match. Each plant originally had its own corner, with sufficient space for future expansion. The aim was to see if one or the other would take over with time, or if the plants would manage to balance each other harmoniously.
I already knew at the outset that the battle wasn’t perfectly fair. While each plant was, in my opinion, about as strong as the other, the growing conditions in the chosen bed, notably heavy loamy soil, very dry in summer, and full sun, clearly favored plants like yarrow. This would have been different in a more humid bed, with richer soil, or with less sun.
Impressive Results
The result was quite extraordinary. After five years with no maintenance whatsoever, not even watering, the six original plants – bee balm, yarrow, sneezewort (Achillea ptarmica), lionhearted, dotted loosestrife and gooseneck loosestrife – were still alive and well. Sternutatory yarrow was the clear winner, having managed to infiltrate the bed from one edge to the other, and yarrow a good second, but both had generally grown between two other plantings, while harming neither. On the other hand, sneezewort and bee balm mingled completely with each other to extraordinary effect: a carpet of white and bright red flowers, while most of the other plants formed well-defined patches, each territory stopping short, or nearly so, with only a little mixture on the edge, in contact with the next.
No Weeds!
The wonderful thing is that while there were a lot of weeds in the beginning (the bed was just a bit of a field whose soil I’d turned over, but nothing more), after five years, all but the pretty goldenrod (so beautiful it’s hard to call it a weed), which produced a clump of yellow flowers here and there across the whole thing, had disappeared, driven out of the bed by plants more vigorous than themselves.
The flowerbed has long since disappeared (the trouble with gardening in spaces that don’t belong to you is that the true owner always ends up reclaiming them one day), but come to think of it, I don’t think I’d ever managed one so beautiful or so low-maintenance!
Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in September 1999 in Fleurs, plantes et jardins magazine.
I love the experiment! And the results!