Landscapers and gardeners beware. A number of ornamental plants have been added to the state's invasive plant list, soon making it illegal to root the showy or aromatic vines, trees and grasses, some of which are staples in Connecticut suburban terrain.

Earlier this month, Gov. Ned Lamont signed into law an update to the invasive plant statute banning the sale, transport, purchase and cultivation of several plants including the Japanese and Chinese varieties of wisteria; the Japanese angelica tree; porcelainberry and mugwort. These plants will all be banned for sale as of Oct. 1.

"Wisteria can really take over stands of trees, similar to how bittersweet grows, it's another, similar woody vine." said Laren Kurtz, invasive species outreach specialist at the University of Connecticut. "Wisteria are a lot prettier than bittersweet, that's why it's a popular landscape plant, but it can get out of control if left to its own devices."

Callery or "Bradford" pear trees were also added to the list and will be phased out over three years to give tree nurseries time to eliminate their stock. They are widely planted as ornamental trees and are known for their beautiful tiny, but stinky, white flowers that bloom each spring, but doesn't bear edible fruit in the fall.

"It's very pretty. It blooms early spring and it can grow almost anywhere and that makes it a problem," said Kurtz.

The plants added this year were banned for different reasons. The two wisteria species which are often found draping purple blossoms from shady porches or pergolas, can also wrap around other plants, smothering them in their vines. Quackgrass and mugwort grow aggressively through their root systems, while Japanese angelica trees are covered in sharp spines and can easily shade out native species.

Some of these plants were introduced as ornamental or landscape plants but have escaped into the wild. Others, like quackgrass, were likely introduced accidentally. Without natural herbivores, these plants can easily move into disrupted habitats, like forest patches in suburban sprawl.

"They tend to dominate the landscape and they have a very fast growth rate," said Jatinder Aulakh, a botanist and invasive plant scientist at the Connecticut Agricultural Experiment Station. "They produce a large number of seeds."

Once established they're often difficult to remove. Some of these plants, like quackgrass, produce chemicals that inhibit the growth of other plants. Others, like Callery pear trees produce a multitude of seeds that can be easily spread by birds.

"They displace our native plants by creating monotypic stands," said Aulakh. "They don't let other (native) vegetation grow."

If invasive plants come to dominate a landscape, it creates cascading problems in the ecosystem. Native insect larvae can't often feed on invasive plants, which cuts down the local supply of food for birds, frogs and small mammals.

"The real problem comes with the native fauna, the native animals and insects," said Kurtz. "They have evolved for millions of years alongside native species. There are very particular relationships between these plants and animals that have evolved over time."

The problem doubles when you consider native pollinators. Butterfly and moth caterpillars are adapted to eat specific, native, host plants, said Kurtz. Without food, they can't mature to help pollinate the landscape.

Making matters worse, some invasive plant species help other invasive insect species colonize the landscape. The tree of heaven, which was already listed on the Connecticut invasive species list, is a preferred food of the invasive spotted lanternfly.

Unfortunately, the spotted lanternfly also feeds on many other different species of plants, said Jim Fredericks, vice president of public affairs for the National Pest Management Association. "Nobody would mind if they just stuck to the tree of heaven."

Spotted lanternflies can cause widespread ecosystem damage by feeding on native plants, which makes the plants vulnerable to fungal infection, said Fredricks. This fungus makes it harder for an infected plant to photosynthesize, as it becomes covered in powdery mold.

Scientists estimate that nationwide, invasive plants have caused about $190 billion dollars in environmental and agricultural damage between 1960 and 2020. Nationally, the cost of controlling aquatic invasive plants, such as hydrilla, is estimated to be about $100 million.

The Connecticut Invasive Plants Council has been trying to get updates to the list for several years. The signing of the law is the first update to the invasive plant ban lists since 2018. Connecticut has regulated invasive plants since 2004, with the Invasive Plant Council making annual suggestions for species to ban.

Kurtz said that people could help by planting native plants and reducing the population of invasive plants on whatever land they managed.

"Each plant has its own weak spot that people can take advantage of to manage them properly," said Kurtz. "Once you've removed those plants from your area, it's important to repopulate with native species that do well in your conditions."