Invasive plants and how to stop them
There was a time when I could look out and gaze adoringly at the perky purple flowers of ajuga, a spring-blooming ground cover, gaily romping across the lawn. Myrtle (aka vinca), another ground-covering charmer, would exude pale blue-purple blossoms—hence the nickname “periwinkle”—to my delight. But that was before I got wise to the wiles of nature. When we bought our house, I knew zilch about gardening, blissfully unaware that these two innocent-looking creepers, relics of previous owners, would turn out to be garden gangsters—“thugs,” as they are also known—muscling out any plants in their path and, I was soon to discover, nearly impossible to evict.
In those early days, I was a virgin of the veldt, given to flights of fancy and trusting of all things vegetative. So it was that I gallivanted through nurseries, naïvely snapping up perennials such as pachysandra and honeysuckle that would quickly become a nightmare; ditto with such shrubs as Japanese barberry and burning bush. What did I know? I just wanted some pretty plants that
would multiply in a hurry and not die on me.
As the garden progressed, however, occasionally conservationists would visit. But instead of covering me with laurels, they would sternly point out plants that were, in fact, environmentally destructive— “Invasives,” they called them—and exhort me to extract them forthwith. Duly chastened, I began to research the subject.
Why Invasives Are Harmful
Invasives—also referred to as “exotics”—are defined as non-natives originally transported either from abroad, such as the previously mentioned ajuga (Asia Minor) and myrtle (China), or as transplants from other regions in the U.S. Because of their sprawling habit and profligate seed production, these plants can reproduce ruthlessly in our neck of the woods—witness the ubiquitous multiflora rose—and can be a bear to restrain. The danger of planting them is that they either displace benign native species by robbing them of light, moisture, and soil nutrients, or, in the case of vining types, by strangling them to death.
In this country there are some 18,000 native plants, 5,000 of which are at risk. Drive around and you’ll see the havoc wreaked upon them by vile vegetal out-of-towners. Along streets and highways, they scramble to the tops of trees, twining around branches and, shroud-like, encasing them in vast webs of hideous vines shading the leaves and eventually causing the trees to expire.
In wetlands, they pose a particularly alarming threat to the ecosystem by demolishing the habitats of such wildlife as birds, mammals, and fish, which rely on wetlands for their survival. Perhaps the biggest villain is purple loosestrife, which spreads with the speed of light: A single mature plant can annually produce up to 2.5 million seeds, each seed capable of remaining alive in the soil for years. An estimated 470,000 acres of wetlands and meadows are pillaged by purple loosestrife in North America each year. It is considered a noxious weed in 19 states, and in 2005, was banned from commercial sale in Connecticut.
But loosestrife isn’t the only horticultural transgressor. To continue the Connecticut example, the state’s invasive plant list includes yellow iris, ground ivy, and Japanese honeysuckle, as well as the abovementioned Japanese barberry and burning bush (my bad). Other plants regarded as invasive are the beloved European lily of the valley, mint, bee balm, and—yes—pachysandra.
How to Control Invasives
Here’s where things get dodgy: once an invasive gets comfortable, it doesn’t want to leave. I have been sidelined by back spasms when attempting to rein in the pachysandra that is bearing down on my prized Siberian iris. I tried to dig it out, only to have it reappear the following year; if there is even a smidgen of roots left in the soil, sure as shootin’, it comes back, thus requiring repeated interventions. This is no mean feat. Pachys, along with other invasives—lily of the valley among them—have stubborn root systems that are so dense, I couldn’t get a spade in the ground. I finally had my muscular lawn guys do the deed.
Of great concern to environmentalists are the invasives that are planted by homeowners, who may not know what they do. Would that I had been aware of the methods gardeners can employ to inhibit, or avoid, the most belligerent species. These methods include:
■ at nurseries, ask only for non-invasive plants, and steer clear of those that are labeled “aggressive”;
■ don’t trade plants with friends or neighbors—you never know what’s lurking amongst the greenery;
■ stick to native plants—a good source for lists of indigenous trees, shrubs and flowering perennials is nativeplants.com;
■ with the most pernicious invasives, best to disinter them, bag them, and take them to the dump; do not toss them onto the compost heap;
■ if all else fails, as a last resort you can use a systemic herbicide that, if carefully applied, kills only the plant itself.
At this juncture, it must be said that the majority of invasives are not barbarians, and one would not wish to malign them. Even those that can be real headaches, in the right place they can be of considerable horticultural value. Pachysandra, for one, prevents soil erosion and is a fine candidate for steep slopes.
In addition, many non-natives, while enthusiastic, aren’t a scourge in our climate (although they can be in warmer climes). The hosta that bedecks the edges of the walkway is a snap to divide; the delicate bleeding heart beneath the rhodies is easily weeded out; and the feathery astilbe in the white garden has never given me a speck of trouble.
Still, there are the true thugs that finally defeated me, viz. the ajuga, which is, more than likely, making lunch out of my entire lawn, and the myrtle that just won’t go away. On these two, though, my hands are clean: I didn’t plant them.
I wish I could say the same of the leafy beasts of the field that I personally invited into my garden, to my everlasting mortification. They stand as a reminder—every damn year, a reminder—of the error of my ways, and I will never, never never ever, do it again.
Besides, who needs the guilt?