Persephone Days: Can Plants Really Invade?
Permaculture means rethinking common notions of “native” vs. “invasive” flora
We’re halfway through summer. Our gardens have gotten away from us a little. Herbaceous perennials sometimes tower over our heads. The flowers are no longer the dainty things of spring, but bold, hearty summer blooms. This is the chaos of Lammas, just before things start to die.
Sometimes, all of this vibrant growth can feel like a bit too much, especially when we’re trying to grow something for ourselves. When a strange plant is crowding out our tomatoes, it’s tempting to label it a weed. Or worse, an invasive.
Much fascinating writing has been done about invasive plant science and the problems inherent in the entire concept. After all, on an Earth that’s always changing in geography and populations, native to when becomes just as important a question as where. Our native plant list wouldn’t be much beyond sycamore trees and ferns if the debate was framed as native to the Cretaceous, for example. The arbitrary line seems to be pre-European invasion of North America, freezing the global process of plant movement and sharing to that single moment in time.
So what counts as “invasive”? Are dandelions invasive because they come from Europe? What about black locust trees, apparently on the North American continent before European conquest, but labeled as invasive by some states in its “native” range because of the ease with which it spreads to new areas? What about poison ivy — technically native to the Eastern US but, come on, its poison ivy. Isn’t it always invasive?
Some seem to believe that the whole concept of invasive species has been created by herbicide manufacturers to move product. As with most such conspiracy theories, there may be a grain of truth in there, but there are also real examples of introduced plants bringing new diseases or causing destruction with their vigorous growth.
It’s complicated; it’s hard to tell which plants actually need to die and which might have uses we risk overlooking.
Many of the most maligned “invasives” belong to a category of plants known as nitrogen-fixers. These fascinating plants, from those confusing black locust trees to ornamentals like wisteria and lupines to sweet four-leaf clovers, are able to essentially create their own fertilizer from nitrogen gas in the air thanks to the help of symbiotic bacteria at their roots. This means that in a worn-out field or a disturbed patch of land next to a highway, nitrogen-fixers can come in and give the whole place a boost without the need for compost or Miracle-Gro. There are even a few nitrogen-fixers, like autumn olive, common along New England roadsides, that produce edible berries while they’re busy rehabbing the soil.
Now imagine one of these plants that’s also a perennial, which as we’ve discussed before, need few inputs or care. A nitrogen-fixing perennial not only barely needs anything from a gardener but also heals the soil and feeds its neighbors. It’s easy to see why permaculturists are obsessed with tracking down obscure species of these to plant between fruit trees or on the back side of gardens.
But let’s keep going with our imaginary plant. Let’s make it even more useful by imagining that it’s edible to people and livestock. Like clovers and other nitrogen-fixers, its leaves would be high in protein, always valuable in a plant food.
Let’s give farmers another bonus by making this imaginary plant drought-tolerant so it needs little, if any, watering during the growing season.
It would be awesome if this were real, right? We could heal our degraded farmland while continuing to feed animals and ourselves. We could plant a bunch of it and create the über-pasture — perennial animal food that builds the soil while it grows.
We can give farmers a break from tilling, planting, fertilizing, and watering. And it comes back every year? This plant sounds great!
Congratulations, we’ve just imagined our way to kudzu, Scourge of the South.
This train of thought mirrors the story of why exactly kudzu — often listed as a prime example of what happens when we introduce dangerous invasives — is in the United States at all. Having been promoted for all of its benefits, when some of kudzu’s negatives became clear, it was blacklisted. Currently, it isn’t used for anything, being seen only as a problem to eradicate.
The situation with Japanese knotweed, more familiar in the Monadnock region, is similar. Introduced to halt erosion, knotweed was championed until it was decided that it grew too well. Like the most horrifying zombie imaginable, this plant can regrow itself from the tiniest root fragment, meaning that digging it up creates more plants rather than removing them. It grows in large stands next to rivers and roads, an herbaceous perennial that towers above our heads in a growing season. Because of the “invasives” versus “natives” hype, people see it and want to kill it, without any thought for why knotweed has moved in or what relationships these plants are involved in.
Japanese knotweed, however, is also a delicious rhubarb-flavored edible. It produces enormous sprays of flowers at a time of year when little else is blooming, and our beleaguered honeybees are big fans of knotweed nectar. It also contains compounds that show promise in treating Lyme disease. Despite the fear mongering, we can look and see for ourselves that rather than smothering out other plants, knotweed can act as a nursery, providing protective shade in which other species may grow.
Ultimately, the solution to the “problems” presented by plants termed invasives lies less in eradication techniques and more in terms of mindset.
In my own yard, I have a couple of autumn olive shrubs, those “noxious invasive” nitrogen-fixers. I often cut the whole thing to the ground and mulch fruit trees with the nutrient-rich leaves and branches, but I’m not in any hurry to eradicate the whole plant. I also have a healthy stand of native poison ivy, which we gave in and treated last year with some carefully-applied glyphosate.
Permaculture isn’t about returning to some idyllic native Eastern forest at a time when chestnuts thrived. Instead, it’s about honestly looking at the situation we’re in and figuring out how to use it to our advantage. We can’t escape the fact that Earth is a big global system, nor can we keep plants contained to where they were in 1492, or 1892, or 1992. Permaculture isn’t about erasing the touches of humanity from the world, it’s about realizing that we are inseparable from nature — and this includes our habit of moving useful plants around the globe and our ability to synthesize chemicals to knock them back.
All any of us can do is work with what we’re given. We can certainly work to root out some of these gifts if they don’t suit our purposes, but in doing so we should keep in mind that every plant — every thing — has relationships with the other living things around it in ways so complex we rarely understand them fully. Every plant — every thing — has drawbacks and benefits. Let’s feast, then, on kudzu-root pudding and knotweed crumble, graze cattle on kudzu leaves and let our beehives fill with knotweed honey — and when we need to, we’ll kill the individual plants that threaten our other projects.