There are two things that can disturb my equanimity in the garden (besides the woodchuck): invasive species growing with wild abandon, and hearing any of my favorite plants described as invasive. I know I’m not alone with the former vexation. But I don’t know too many people who get as hot under the collar as I do whenever someone lumps a perfectly garden-worthy plant in the same basket with horrors like goutweed (Aegopodium podograria), Rosa multiflora, burning bush (Euonymus alata), barberry (Berberis thunbergii), or purple loosestrife (Lythrum salicaria) simply because it spreads from the roots or reseeds.
I think it’s great that we gardeners are always looking out for each other but I believe that the word “invasive” is overused. More to the point, I believe that the more arbitrarily the word is used, the faster it loses its meaning. “Invasive” should be reserved exclusively for those species that pose an actual threat to our ecosystem. Plant species that are capable of outcompeting the native flora necessary for supporting native insects and wildlife and providing essential services like water filtration and erosion control.
Invasives are truly scary and we all bear a responsibility, especially if we live near sensitive wild ecosystems, to remove — or at the very least refrain from planting — anything actually and potentially invasive. By using the word to describe any old plant that grows vigorously, we risk losing sight of that. And it makes it so much harder than it needs to be to determine what to avoid planting. The sad thing, especially for new gardeners who might be relying heavily on us and the internet as their guide, is that a whole lot of great plants are apparently off limits.
It shouldn’t be that hard to restrict our usage. The URI Master Gardeners’ website provides links to helpful references as well as listing locally invasive species (www.urimastergardeners.org/invasive-plants-rhode-island). You don’t even need to be a gardener to be familiar with the most unwanted on those lists. My chef and carpenter, catching the title of this essay, remarked that the Oriental bittersweet vine (Celastrus orbiculatus) reaching its telltale orange roots into our yard, binding tentacles to the tops of our junipers, and sending its seeds in birds’ bellies far and wide from our neighbor’s untended lot, warrants a string of invectives.
The trick is remembering that just because a plant outgrows our expectations doesn’t necessarily mean it’s a monster. Not if we are capable of editing and managing its growth and keeping it inside property lines. Vigorous plants can fill a fabulously multi-colored gray area in our gardens—and do so inexpensively, which is part of why I like them so much.
I have a guess why some gardeners prefer to keep it black and white: most of us find it excruciatingly difficult to evict healthy plants. Unless we call them weeds. I have a hard time letting go of certain favorites too, even when there are way too many. But I also have come to prefer designing by subtraction. Self-sowers and spreaders give me the chance to see what does and doesn’t look good before making changes while also supplying plenty of extras to tuck into new combinations.
One of my favorite perennials is a 12-foot tall stunner with gray-green oak leaves and feathery flower plumes that spreads willingly from shallow roots. Rather than call plume poppy (Macleaya cordata) invasive (which it isn’t and I wouldn’t like it one bit if it was) a friend of mine once compared growing it in his garden to jumping out of airplanes. I’m no daredevil so I think of it as merely enthusiastic. Rambunctious maybe. Generous, definitely. I believe those are much better words for a whole range of plants way too pretty and/or useful to be dismissed and disparaged as “invasive.” And whenever I can’t say something nice, words like “aggressive thug,” “bully,” or “the devil” paint a sharp enough picture.
Kristin Green is the interpretive horticulturist at Blithewold Mansion, Gardens & Arboretum and author of “Plantiful: Start Small, Grow Big with 150 Plants that Spread, Self-Sow, and Overwinter” (Timber Press). Follow Blithewold’s garden blog at http://blog.blithewold.org.