Deep roots: Aggressive plants effective to some, a nuisance to others as growing season begins

Yahoo

25-03-2025

Mar. 25—The Capets family of Murrysville has a positive relationship with bamboo, a grass native to the Asian continent that grows tall and spreads quickly.
They've been using it for more than a decade to screen their front yard from nearby traffic on Sardis Road. And it works well, forming a near-complete wall about 25 feet high.
"We like it," Sean Capets said. "It sends roots about 10 or 20 feet into the yard, but I run them over with the mower and try to keep a straight edge. A little while back, I used a backhoe and tried to rip out as many of those roots as I could."
A few miles east, however, Teri Walborn of Delmont has a very different relationship to the plant. After neighbors planted it next door 15 years ago, it grew to the point where it was damaging Walborn's property.
"They get the beauty of it, they get the privacy. And my husband and I get the mess," Walborn said.
Spring has arrived, marking the start of a planting season that will extend through June. But the season also includes a host of invasive plants, introduced intentionally and accidentally over the centuries.
Native flora has evolved in harmony with native wildlife. But invasive plants, in many cases, do not have any natural consumers and can spread unabated.
"A big reason why invasives, especially from Asia, can do so well here is they're found along the same latitude line as North America," said Crystal Armagost Volchko, owner at Rust Belt Natives, a Pittsburgh greenhouse that focuses on native plants. "But they don't belong here, so they don't have the other plants, predators and pests who normally would keep them in check."
Volchko said part of the reason fewer butterflies and fireflies are flitting around backyards and roadside meadows is that fewer and fewer of their favorite native plants are around.
"We're losing a lot of our key species because people haven't been focused on keeping the keystone plant species they need to survive," she said.
While bamboo is non-native and invasive from a biological perspective, it is not on the official list of invasive plants in Pennsylvania, where both an agricultural group and a committee convened by the governor meet regularly to discuss whether new plants should be added to the state's list.
Going native
At Arona Road Greenhouse in Hempfield, co-owner Sarah O'Hern's stock of springtime plants looks different than a decade ago.
"We've stopped selling English ivy and periwinkle," O'Hern said. "They're not on the official invasive list, but they can spread and become a problem. It's a battle, because a lot of people want an aggressive ground cover for a hill they don't want to mow."
The grass varieties the greenhouse sells has also changed over the years, as they began shifting away from attractive-yet-invasive species, O'Hern said.
"One thing that everyone wants is a butterfly bush, which is also invasive," she said. "We've really cut back our selection and only sell a couple of sterile varieties that don't produce seeds like the old-fashioned ones."
O'Hern said plant nurseries have shifted to try and put more of a focus on native plants, but they aren't always the most eye-catching.
"The younger generation is even more aware of the importance of planting natives," she said. "But when people come into an ornamental greenhouse in the spring, they're looking for big colorful flowers. They see the native plants which aren't quite as cultivated and a little more spindly. We do try to focus on native cultivars that are a little more attractive."
Invasives everywhere
Pennsylvania forests are traditionally thought of as lush, green and full of plant life — and they are. But if non-native species were removed, there would be surprisingly little green left over.
"You can look at a modern forest and think it's wonderful, but a lot of the green you're seeing is plants that are competing with the native flora, or that have already driven out some natives," said Mason Heberling, associate botany curator for the Carnegie Natural Museum of History, which opened "Uprooted" on March 22, an exhibit focused on its invasive plant collection.
Forests across the state changed drastically during the height of the commercial logging era, when nearly all of the trees in Pennsylvania that could be used for ship masts or building timbers were cut down. Old-growth trees such as white pine and hemlock were almost completely wiped out. As the state's forests grew back, oak-dominant hardwoods took over. And as invasive species were slowly introduced, whether intentionally or by accident, they began to make a permanent home and crowd out native flora.
"We have invasive plant specimens from Pittsburgh dating back to the 1860s," Heberling said. "We're using our collection and the research we're doing with it to contextualize the topic of invasive plants."
Because invasives don't belong, in many cases the local ecosystem has no way to keep them in check and they can proliferate quickly, crowding out native plants.
A few examples that can be readily seen in just about any Pennsylvania woodland are the multiflora rose (locally and colloquially among the plants referred to as "jagger" bushes), Japanese stiltgrass and knotweed, which museum officials are using to tell the story of how human culture and invasive horticulture are interconnected.
Japanese barberry can be found in at least half the front yards in Plum's Holiday Park neighborhood. Landscapers loved it because deer didn't eat it. But that same quality made it an attractive home for black-legged ticks, and birds spread its seeds through their droppings, giving it a foothold in the state's woodlands, where it shades out much of the native undergrowth.
"A lot of species aren't fully appreciated as invasive until decades later," Heberling said. "Multiflora was introduced intentionally. Same with something like garlic mustard, which actually has chemicals in it that inhibit other below-ground organisms. Japanese stiltgrass reseeds every year and is becoming a dominant part of our forests."
Why not bamboo?
Unchecked, bamboo grows quickly and spreads rapidly. What was once a small patch along Golden Mile Highway near the Plum-Murrysville border has quickly spread in a wide stripe to the top of the hill. There is another large patch across from the Holiday Park Volunteer Fire Department along Abers Creek.
Ben Dunigan, director of horticulture at Phipps Conservatory in Pittsburgh, said that patch probably explains why there is a small bamboo stand growing behind Holiday Garden Center, located a half-mile downstream and nowhere near any homes or landscaping.
"One of the things that will spread it is water and flooding," Dunigan said. "Heavy rain could easily wash some of it downstream where it could get reestablished."
Bamboo's primary growth mechanism, however, is probably why it is not yet on the state's noxious weed list, despite previously being considered for inclusion.
"It is technically a flowering plant, but if you ask people, almost no one has ever seen a bamboo flower," Dunigan said. "It's not scattering a ton of seeds in the winds. It primarily spreads underground through rhizomes."
A rhizome is a horizontal, underground stem a few inches below ground that sends up lateral shoots as it grows. Canna lilies, ginger and horseradish also spread via rhizomes.
"Bamboo doesn't bloom and produce a vast amount of seeds, which is a big part of why it's not on the invasives list," Dunigan said. "If you have a plant whose seeds are being spread by the wind and by things like bird droppings, that makes it a much bigger threat to native plants."
'A symptom of changes'
A good many of Pennsylvania's invasive species have their roots in Asia, and Heberling said the legacy of invasive plants in the U.S. is very much tied to international trade and travel.
Bamboo, for example, came to the U.S. via Chinese immigrants who worked on America's railroads, who brought it and planted it as a reminder of their home country, Heberling said. But something as simple as a few seeds stuck in the tread of a shoe can introduce a new plant into the ecosystem.
"Species have adapted to the changes introduced by humans," he said. "We've changed the environment in many, many ways, and invasives are a symptom of the landscape changes humans have made. Invasives are sort of passengers. They're not driving, but a lot of times they're along for the ride."
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State monitoring effort
The Pennsylvania Department of Agriculture's Controlled Plant and Noxious Weed Committee monitors invasive species.
The group meets twice annually to consider adding new plants to its official list of state invasives. In addition, the Governor's Invasive Species Council makes recommendations to the committee, which was formed in 2015.
"Prior to that, Pennsylvania had no means of banning the sale of a plant that was harmful to farmers, harmful to the environment or creating problems," said agriculture spokesperson Shannon Powers.
When people — typically farmers, Powers said — ask the committee to consider adding a plant to the list, its members look at the plant's impact on industry, whether banning its sale would harm the horticulture industry and other factors.
"There are different levels of noxious weeds," Powers said.
For example, at the top of the list is giant hogweed, which is not only invasive but produces photo-toxic sap that causes blisters, chemical burns and scars if it touches human skin. It is a truly dangerous plant and is ranked as a Class A noxious weed, meaning it is geographically limited and efforts are underway to eradicate it.
Japanese barberry, which was added to the list in 2021, is a Class B noxious weed, meaning it is already widely established and eradication at this point would be a futile exercise. But its sale by plant nurseries is now banned. The landscaping industry adjusted quickly to the barberry ban, with commercial growers breeding new cultivars that are sterile and do not reseed.
Other common invasives such as Japanese stiltgrass, garlic mustard, knotweed and tree-of-heaven also are in the Class B category.
Patrick Varine is a TribLive reporter covering Delmont, Export and Murrysville. He is a Western Pennsylvania native and joined the Trib in 2010 after working as a reporter and editor with the former Dover Post Co. in Delaware. He can be reached at [e-mail].