Invasive Plants: What’s A Gardener To Do?
In recent years, I have become increasingly aware of the problem of invasive plants. I am not referring here to those uninvited plants (aka weeds) that invade our flower beds and crowd out the plants we are trying to grow. And I’m not referring to plants that we’ve invited into our gardens only to discover that they don’t “play nice” with others (aka “garden thugs”). When I talk about invasive plants, I mean exotic plants that we invite into our gardens, but that have a propensity to escape from the garden and do serious damage to native ecosystems.
Here in the northeast corner of the United States, three of the most problematic invasive plants are purple loosestrife (Lythrum salicaria), Japanese barberry (Berberis thumbergii), and Japanese knotweed (Fallopia japonica or Polygonum cuspidatum). These are all beautiful plants, and it is easy to see why they were desired by gardeners who had no idea what kind of disaster they were putting into motion.
|Purple loosestrife (Lythrum salicaria) is a beautiful plant that can be breathtaking when masses of it bloom together. But those fields of purple are crowding out native cattails and destroying marsh habitats.|
Some gardeners avoid the problem of unwittingly introducing invasive exotics by growing only native plants. I’m not willing to take this route. Although I include native plants in my garden, most of my perennials and many of my favorite plants are, in fact, exotics (some of which have been grown here for hundreds of years). But if I’m going to bring exotic plants into my garden, I have an ethical responsibility to make sure that I’m doing so in ways that do not harm native ecosystems.
After much thought, I’ve identified three steps I can take to garden in a way that is ethical and sustainable:
- Educate myself about invasive plants. A browser search for “invasive plants” + a place name (in my case, “invasive plants + Maine”) will usually identify links to government or university sources that list locally invasive plants. Other good sources of information for the United States are the Plant Conservation Alliance, which provides fact sheets for a list of the most invasive plants, and the Invasive Plant Atlas of the United States, which has extensive lists of invasive species and allows you to look at a map showing where any given invasive species is a problem. (Unfortunately, the Invasive Plant Atlas does not allow you to click on a part of the map and see what species are invasive in that location.) Both sources provide information on native plant alternatives.
- Take responsibility for invasive exotics growing in my garden. I am not growing any of the plants listed as a serious problem by the state of Maine, but I do have one plant in my garden that may be problematic, Spirea x ‘Magic Carpet.’ Since I first learned that Spirea japonica is invasive in eastern woodlands, I have been engaging in a process of denial and wishful thinking about my beloved ‘Magic Carpet’ shrubs. This plant is sometimes listed as a hybrid of Spirea japonica and sometimes as a hybrid of Spirea bumalda, so I tried to convince myself that it wasn’t really one of those invasive S. japonicas. Then I thought that, since it’s a hybrid, maybe its flowers are sterile. This week, I finally moved beyond wishful thinking and learned the facts about ‘Magic Carpet.’ When I did a browser search on the plant, I quickly found the patent application from the breeder, which clearly lists it as a cultivar of Spirea japonica. I also found accounts from gardeners of self-sown seedlings from ‘Magic Carpet,’ so it’s not sterile. Finally, although the state of Maine does not list Spirea japonica as invasive here, the Invasive Plant Atlas shows infestations of it in one part of Maine, the county that borders mine, about 10 miles away. And my house is surrounded by exactly the kind of woodland that Spirea japonica is known to invade.
- Take action to stop the escape of invasive exotics from my garden. Now that I know my Spirea ‘Magic Carpet’ is a potential problem, I need to do something about it. According to the fact sheets, Spirea japonica spreads when its seeds are washed by the rain into wet areas and stream beds, and the seeds can remain viable for many, many years. The first thing I need to do is to stop the seeds from spreading; I can do this by deadheading the spent flowers before they set seed. Since seed may have already spread into the woods, I also need to walk the woods around my house a couple of times a year, looking for signs of Spirea seedlings. By repeatedly cutting any seedlings back to the ground, I can keep them from maturing, flowering, setting seed and invading the native woodland ecosystem.
Faithfully deadheading my Spirea plants and scouring the woods for escaped seedlings is going to take a serious commitment of time and energy; but by making that commitment, I can help to preserve and protect my native woodlands and the species that depend on them. Taking responsibility for my exotic garden plants will also make me more aware of how my garden interacts with the surrounding environment and thus help me to garden in a more responsible and sustainable way.