Fighting the spread of invasive plants in the wild begins with the weeds in your own backyard
In Portland, Oregon, volunteers remove English ivy from a park.
SEVERAL YEARS AGO, I had a choice between planting a Bradford pear or a flowering dogwood in my front yard on Capitol Hill in Washington, D.C. I selected the pear tree. It was the wrong decision.
While both trees may look lovely during springtime, flowering dogwoods—native to eastern deciduous forests—produce berries that ripen in autumn, providing nutritious, high-fat food for more than 60 bird species, including thrushes, catbirds and other migrants. The trees are also host plants for many kinds of caterpillars, which birds, from chickadees to warblers, need to nourish their young during the spring-through-summer breeding season.
Bradford pears, on the other hand, are native to Asia and “have very little ecological value” in North America, says invasive species specialist David Coyle, an assistant professor of forestry and environmental conservation at South Carolina’s Clemson University. “They support few, if any, native insects,” he adds, and their fruit is merely “junk food” for birds.
Even worse, these nonnative trees can outcompete natives such as oaks and hickories that do offer sustenance for insects, birds and other wildlife. Today, invasive Bradford pears (and the related Callery pears, their wild cousins) are weed trees that have spread far beyond city streets and private yards across much of the eastern and midwestern United States. They are so harmful to natural habitats that the state of South Carolina will ban the sale of both kinds of tree by nurseries beginning in 2024.
Personal choices can make a big difference in the nation’s war on weeds. “People should always plant natives in their yards,” says Jeanne Braha, executive director of the Rock Creek Conservancy, a nonprofit group battling dozens of invasive species that have escaped from yards and gardens into Rock Creek Park, a 1,700-acre urban oasis in Washington, D.C. The intruders include porcelain berry, oriental bittersweet, English ivy and Chinese wisteria.
Each year, the conservancy enlists hundreds of volunteers to remove invasive plants from the park. “One of the problems with nonnatives when they invade,” says Braha, “is that they smother spring-blooming ephemerals” such as violets, trout lilies and mayapples that provide food for mining bees and other early-emerging pollinators. But natives will return once invasives are cleared out, she adds. In one demonstration site where weeds were removed, mayapples now grow on hillsides where they hadn’t been seen for a decade.
In Vancouver, British Columbia, a similar group of 700 volunteers—called Ivy Busters—have removed more than 200,000 square feet of English ivy from the city’s Stanley Park. They believe it will take more than 50 years to completely rid the park of this aggressive vine, which has taken over many natural areas along the Pacific Coast, from California northward into Canada.
Volunteers are critical in the struggle against invasives, says Perry Grissom, a recently retired restoration specialist at Arizona’s Saguaro National Park who has worked to remove several nonnatives—including buffelgrass and fountain grass (both originally from Africa)—with the help of volunteers. Buffelgrass “has the potential to wipe out native saguaros … and changes the ecosystem,” he says. When it moves into an area, baby cacti disappear, and native wildlife such as desert tortoises and pocket mice decline as their food decreases. Fountain grass, planted by many homeowners as an ornamental, changes the frequency of fires and is a threat to velvet mesquite and other desert plants.
If volunteering to pull plants from a park is not an option, you can still make a big contribution simply by policing your own yard. The first step is to take out any invasives you may have planted. It’s also important to remove weeds that pop up in your garden on their own, especially during summer when they spread aggressively.
If you have only a few invasive plants, mechanical control methods—hoeing or pulling out weeds by the roots—are a good option. Another approach, especially for smaller invasives, is to use vinegar to kill them. (Combine four parts vinegar to one part water in a spray bottle and saturate the weeds.) If you have a large area or a lot of ground cover to eliminate, smothering the unwanted plants with heavy-duty plastic will work, although that can take several months or longer.
Unfortunately, removing invasive weeds is not a one-time exercise but a never-ending task. “It’s like making your bed every morning,” says Braha. “It has to be done over and over again.”
Doreen Cubie is a regular contributor based in Arizona.
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