You might assume that if a plant is bad for the environment where you live, it won’t be for sale in your region. Unfortunately, it doesn’t always work that way. Many states do not have regulations prohibiting the sale of plants that have been identified as invasive, says Bethany Bradley with the University of Massachusetts Amherst. And even in the states that do regulate invasive plant species, legislation lags far behind the research, she says.
To get a sense of how widely invasive species are being sold in the United States, she and her colleagues used an online search engine and a database of nursery catalogs to investigate. Their findings: 61 percent of 1,285 ornamental plant species identified as invasive in the U.S. remained available to purchase. Their research revealed vendors offering invasive plants in all of the lower 48 states.
What Is an Invasive Plant?
Invasive plants are those introduced from other areas—but not all non-native plants are invasive. To be considered invasive, a plant needs to cause harm to ecosystems or economies. In the case of ecosystems, the new plant can compete for resources and might not be a good source of food or habitat for local wildlife. It can also be a bad a match for native pollinators, which tend to specialize in the few types of flowers they co-evolved with. “So if you have an invasive species that outcompetes or grows over the top of the handful of species those specialist pollinators need, then they’re basically done for,” Bradley says.
Before you commit to purchasing plants for your landscaping, search the name of the plant along with the word “invasive.” “If you end up with a bunch of hits, maybe avoid that species,” says Bradley. Another good resource is the Invasive Plant Atlas, a collaborative project between the National Park Service, the University of Georgia Center for Invasive Species and Ecosystem Health, the Invasive Plant Atlas of New England, and the Lady Bird Johnson Wildflower Center.
You can also cross these known troublemakers off your list.
- Bethany Bradley, Professor of Biogeography and Spatial Ecology, University of Massachusetts Amherst
- Karey Windbiel-Rojas, Associate Director for Urban & Community Integrated Pest Management with the University of California Integrated Pest Management Program
Bamboo
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Most of us think of bamboo as eco-friendly. And in its native tropical and subtropical regions, it plays an important role in storing carbon and providing materials for furniture, flooring, paper, and other products used worldwide.
But after being introduced in the U.S. as a landscape grass in the late 1800s, non-native bamboo became invasive, overtaking existing vegetation and preventing new forest growth as it spread through underground rhizomes. It has also harmed insects and wildlife that relied on displaced native species for food and shelter.
Three species—common bamboo (Bambusa vulgaris), golden bamboo (Phyllostachys aurea), and Arrow bamboo (Pseudosasa japonica)—have been listed as invasive in the mid-Atlantic and Southeast as well as some sites in the western and southwestern U.S.
“The bamboos also are just really fast-growing and really good at sending out runners and getting into your neighbor’s yard and then getting into ecosystems,” Bradley says. “I would avoid any species of bamboo.”
Barberry
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Early settlers brought barberry from Europe and used it to create ornamental hedges and to contain livestock. They also used its fruit to make jam and yellow dye. But it quickly became invasive, as well as a host for black stem rust, a disease that continues to threaten wheat production in the U.S. Introduced later as an alternative, Japanese barberry also proved invasive.
Both generate copious seeds that germinate readily and spread—sometimes after being eaten by wildlife—into forests throughout the northeast and west as far as Wyoming. Once established, they form dense walls that restrict animal movement and outcompete native plants. Their thick foliage also serves as a tick magnet and breeding ground.
Brooms
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Highly competitive and fast-growing, broom shrubs form dense stands that crowd out other plants, block wildlife movement, and create a dangerous fire hazard.
“They’re pretty, but they produce a lot of seeds,” says Karey Windbiel-Rojas with the University of California. “And if they escape from your landscape, or if you are near a wildland area, they can spread into the wild lands very rapidly and become invasive.”
Four non-native species are now considered invasive in North America: Scotch broom (Cytisus scoparius), Portuguese broom (Cytisus striatus), Spanish broom (Spartium junceum), and French broom (Genista monspessulana).
Euonymus
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Two popular Euonymus species have been reported as invasive. Striking burning bush (Euonymus alatus) is known to be invasive from New England to northern Florida and the Gulf Coast, as well as in Illinois and Minnesota. A common hedge and foundation plant, it prodigiously produces seeds that birds then disperse into forests, woodlands, coastal scrublands, and prairies, where it forms dense thickets as it outcompetes native vegetation for light, soil nutrients, and space.
Winter creeper (Euonymus fortunei) has been reported to be invasive in most of the states in the eastern half of the U.S. Birds and wildlife spread the seeds for this vigorous vine, which then displaces tree seedlings and other native plants as it covers the ground in forest openings. “It has been assessed by every single invasive plant council in the Northeast, and they’ve all identified it as high risk and having impacts,” Bradley says. “But no one has been able to successfully regulate its sale because it’s so profitable as an ornamental.”
Fountain Grass
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Native to northern Africa and western Asia, showy Pennisetum setaceum is sold widely in the U.S. as an ornamental grass. But its seeds carry easily on wind, water, animals, and vehicles. This has enabled it to spread aggressively into forests and rangelands in California, Nevada, Arizona, New Mexico, western Oklahoma, and the Texas panhandle. Even fountain grass plants sold as infertile can be pollinated by fertile varieties and spread, the USDA warns.
By rapidly outcompeting other species, fountain grass has diminished vital food and habitat for frogs, toads, and other wildlife. It’s also highly flammable and has greatly increased wildfire potential across the West and Southwest.
Mexican Feather Grass
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Stipa/Nassella tenuissima is native in North America, but only to mountains in west Texas and adjacent New Mexico south to Central Mexico, according to the Lady Bird Johnson Wildflower Center. It’s not invasive within its range. But it has become popular—and problematic—elsewhere, including California, where it has been listed as an emerging invasive species.
“It establishes really fast, and it grows fast, which is why people like it,” Windbiel-Rojas says. “But then it spreads quickly and can contribute to fire hazard.” It’s also harmful to grazing animals and biodiversity.
Miscanthus
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Also known as zebra grass and Chinese silver grass, Miscanthus sinensis escapes from ornamental plantings via underground rhizomes and wind-dispersed seeds. From there, it invades roadsides, forest edges, untended fields, and other areas, largely in East Coast states and pockets throughout the U.S.
While it was previously believed that miscanthus and its cultivars bloomed too late to produce viable seed in northern areas, newer studies have shown that it can become invasive in northern states, too, according to the Chicago Botanical Garden, which conducted one of the trials.
Pampas grass
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Big, showy Cortaderia selloana has become a big, invasive problem in California. Native to South America, it was introduced to the state in 1848 by nursery operators.
Now, it has overtaken native ecosystems up and down the coast and west into the wildlands and forests of the Central Valley and beyond, where its sharp leaves are highly undesirable as food and shelter to birds and other wildlife and can actually harm them.
“A single Pampas grass inflorescence or plume can produce 100,000 seeds a year,” Windbiel says. “And they can blow in the wind 20 miles away.” That launches a cycle in which it rapidly reproduces, throwing shade that prevents even tree seedlings from germinating and then dries down, becoming a fire hazard.
Periwinkle
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We know. It’s hard to believe that beautiful and reliable periwinkle, or myrtle, is an invasive plant. But Vinca minor has been classified as invasive throughout the eastern U.S. and farther west, including Michigan, Wisconsin, and Oregon.
And its cousin, Vinca major, also known as bigleaf periwinkle, has been reported as invasive up and down the West Coast, in most of Arizona, and in individual locations across the south and southeast.
Both spread through sprawling stems that form roots. Even a small fragment of plant or root carried on a waterway or along a drainage area can reach an untended forest area or canyon bottom, where it can eventually become a massive, dense mat that chokes out native plants and degrades animal habitat. It is also known to host the bacterium that causes Pierce’s disease, which is deadly to grapevines.
Tree of Heaven
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Brought to the U.S. from China in the late 1700s, Ailanthus altissima (also known as Chinese sumac) is no angel. While it was sold in nurseries in the 1800s and valued for its rapid growth, it fell out of favor as people battled its out-of-control spreading and foul odor.
It is now reported as invasive in more than 30 states across the U.S. It spreads through seeds and creeping root systems that produce copious suckers, creating dense thickets that crowd out native species and damage pavement and building foundations.
It also secretes a chemical into the soil that suppresses the growth of other plants, and it hosts the spotted lanternfly, which damages fruit and ornamental trees, grapevines, vegetables, and grain crops.
