What’s to love about native plants that spread like crazy? Everything! Enlist these hardy troopers to help reclaim habitat from invasive species.
They were the last lonely leftovers: seven pint-size transplants I couldn’t even give away. Other beauties—boneset, coneflowers, bee balms, asters—had flown off the shelves of my cubicle wall, where a “Free to Good Home” sign invited friends and colleagues to give them a new spot in their own gardens.
But the golden ragworts, still small and fairly nondescript, had a harder time selling themselves. It didn’t help that their name sounded like “ragweed,” the plant everyone loves to hate, or that I repeatedly responded with an enthusiastic “Yes!” when asked: “Does it spread?” My fellow gardeners, trained to panic in the face of plants that refuse to be kept down, backed away in terror, eyeing the pots as they would a petri dish of ebola virus.
So it was that the remaining stash of this underappreciated groundcover—which feeds bees and shelters many other creatures—ended up back in my yard, though not in its rightful place in the ground. Putting the plants aside under some sassafras trees by our driveway, I intended to give them a better home, but life got in the way. As the leaves dropped and the snow fell and one season passed into another, there they sat, neglected and trapped in their plastic pots.
That spring, though, the plants gave me an unexpected gift in spite of my poor stewardship. As I headed past the driveway to tackle the onerous spring ritual of removing garlic mustard (Alliaria petiolata), a persistent invasive species, I discovered the little ragworts had gotten a head start on the task. Refusing to be held captive, their roots had burst forth from the holes in the bottom of the pot and rambled fearlessly into the garlic mustard patch.
To understand what a revelation this was, it helps to know a little about garlic mustard. Originally from Europe and Asia, it’s allelopathic, releasing chemicals that inhibit the growth of other species. It’s a threat to forest understories in the U.S. and Canada and also to the West Virginia white butterfly, which seems to mistake garlic mustard for its host plant, laying eggs of caterpillars doomed to die on leaves they can’t eat.
But in my yard, garlic mustard has finally met a worthy contender. Watching a habitat-harming plant succumb to an equally hardy native has opened my eyes to a more creative, life-affirming method of curtailing invasives on my property. Since it’s not in my nature to want to fight nature, I find the process of cutting, digging and pulling plants—no matter their provenance—a little heart-wrenching. And because I don’t want to support products that harm the land and the creatures who survive off it, I avoid herbicides. Besides, I’d rather not remove any vegetation that’s providing even minimal habitat if there are few other alternatives for nesting and food. Even my preferred, seemingly harmless method of laying down cardboard to kill grass has its consequences, potentially smothering the homes of native bees and other creatures nesting in the ground.
The idea of adding more wildlife-friendly plants while gradually removing less helpful ones, then, appeals to my sensibilities much more than declaring chemical and mechanical warfare to clear the land—and, in at least some cases, it can be more effective in the long term. Here are a few experimental methods that have proven successful on different types of sites, including my own.
Following the ragwort’s unexpected coup, I added more to the 12-by-12-foot garlic mustard patch and watched delightedly as it claimed the whole territory. And it took only three years—about the same length of time a similar experiment played out in the yard of Sue Barton, a University of Delaware associate professor and extension specialist. In her original attempts to eliminate Japanese stilt grass (Microstegium vimineum), an invasive species that crowds out other plants, she’d tried all the standard approaches—mowing, herbicides, replanting with low fescue, and pulling the remaining scattered interlopers that sprouted. Ultimately, the effort had failed. “It’s now just solid stilt grass,” she says.
When she later confronted a second patch of stiltgrass in the backyard, Barton changed her approach, manually weeding out the space before planting a combination of native woodferns (in the Dryopteris genus) and Japanese painted ferns (Athyrium x ‘Branford Rambler’). By spring, the fall project had taken hold and the plugs were thriving. “But the stiltgrass started to grow, and so that summer, it was like a treasure hunt, looking for the little fern plugs in amongst the two-feet-tall stilt grass,” Barton says. She again weeded the stiltgrass out by hand, and in the third year, the 1,000-square-foot space had filled in entirely with ferns. Disliked by deer, the plants were also large enough to shade the ground and prevent further germination of stiltgrass.
“I don’t necessarily know that ferns would work in every situation—what works in one instance is not guaranteed to work another,” says Barton. “It’s just our best guess.”
2. Employ Defensive Linebackers: Practice preventive planting.
Some native plants can hold their ground even against the most impressive offensive lineup. At one Maryland site, Southeastern wild rye (Elymus glabriflorus) has been observed staking its claim in a garden otherwise overtaken by invasive Canada thistle. Proactively planning for this type of “competitive exclusion”—a term for describing species duking it out for the same resources—is the best way to ensure long-term sustainability in landscapes expected to thrive on their own, says Claudia West, coauthor of Planting in a Post-Wild World: Designing Plant Communities for Resilient Landscapes.
“I’m on a consistent mission right now to find highly aggressive and thuggish native plants,” she says. “I am looking for native species that have all the ecological value, that can outcompete some of the invasive stuff we’re dealing with.”
I’d rather have a very thuggish, vigorous native plant take over an area than have it covered in honeysuckle or autumn olive. … We’re looking for plants that can stand their ground. —Claudia West
In planting projects she undertakes as the ecological sales manager for North Creek Nurseries, West sometimes sneaks in tough native spreaders like wild petunia (Ruellia humilis) and native sedges—species that provide food and cover for wildlife who’ve evolved to depend on them. Though some of the plants won’t leave room for much else, the tradeoff is worth it. “I’d rather have a very thuggish, vigorous native plant take over an area than have it covered in honeysuckle or autumn olive, especially for landscapes that we know from the beginning will not receive a lot of care,” says West. “Think about all the storm water maintenance along highways. Think about parking lots. We’re looking for plants that can stand their ground.”
It’s a useful strategy in many home landscapes as well, especially for gardeners with a heart and mind for helping wildlife but a property covered in turfgrass edged by invasive vines and shrubs. Preventing further encroachment of these plants in my own yard are mountain mint, blue mistflower, bee balm, elderberry, gray dogwood, Pennsylvania sedge and other stalwart defenders. Planted little by little over many seasons in areas where they can freely spread their wings—and roots and seeds—they’ve started to fill in previously barren or invasive-prone spots in our two acres.
3. Recruit Volunteers: Encourage self-starters.
“If I do nothing, what will happen?” asks pioneering landscape designer Larry Weaner in his 2016 book, Garden Revolution: How Our Landscapes Can Be a Source of Environmental Change. While not advocating for a cessation of gardening, Weaner encourages readers to use the question as a guiding principle for creating an ecological landscape or restoring a degraded site. In other words, what native plants are already lying dormant in the land, waiting for us to stop mowing them down? What valuable seeds might migrate into the garden on the breeze or in the bellies of birds? Weaner has seen this strategy come to fruition in his planting projects, as when he added Indiangrass (Sorghastrum nutans) to a client’s meadow and later saw it thriving in an adjacent lawn that a neighbor had let go—and grow.
Refusing to be held back, such unexpected visitors are an increasingly common occurrence on my property as well. Learning who they are and how they grow has been one of the great joys of gardening (or what I’m starting to think of as “un-gardening.”) Some are diminutive, like the blue-eyed grass (Sisyrinchium angustifolium) that came up singly in a patch of old turfgrass by our back deck. Others make themselves known with wild abandon, like the hyssop-leaved thoroughwort (Eupatorium hyssopifolium) that shot up high above an old bulb garden we inherited from previous homeowners, beckoning fall-migrating monarchs. An entire field of broomsedge (Andropogon virginicus) and purpletop grass (Tridens flavus) graces our backyard where there used to be only mowed lawn, making way for more wildflowers—and eventually trees—with each passing year.
Two summers ago, as I pondered how to address invasive ground ivy (Glechoma hederacea) in the front yard, my husband stopped mowing there so the bees could feed on the plant’s early flowers and nest in the bare patches of soil between. By fall, when the ground ivy had continued to spread and I was still plagued with indecision, we discovered that nature had been thinking much more creatively. An inspection of the area revealed nine baby Eastern red cedars peeking up through the leaves, humbling me once again: The previous spring, I’d spent $30 on three diminutive plugs of the same species, and here were three times as many coming up for free. They were healthy and strong and ready to provide nesting, cover and fruit for many bird species, as well as food for foxes, rabbits, raccoons, and butterfly caterpillars who call that tree species home.
Ground ivy, the plant I didn’t want, was serving as a kind of nurse plant for the one I did—something that could only have happened when we’d stopped cutting everything off at the knees.
For more tips on working with nature in your garden, check out my new book, The Humane Gardener: Nurturing a Backyard Wildlife Habitat, due for release from Princeton Architectural Press on April 18.
Featured image at top: A mountain mint (Pycnanthemum flexuosum) showed up on its own near a patch of golden ragwort. An Eastern tiger swallowtail signaled her approval. (Photo by Nancy Lawson)