Wisteria is a popular and fragrant flowering vine known for its dramatic cascading blooms, making it a classic feature in many landscapes. This woody climber, however, is also infamous among gardeners for its incredibly vigorous growth and potential to overwhelm structures and other plants. The question is whether this reputation stems from simple garden aggression or true ecological invasiveness. Understanding the difference between these two behaviors is the first step in determining the proper management of the plant in a yard and the wider environment.
Defining the Threat: Aggressive Growth vs. True Invasiveness
A plant is “aggressive” if it grows quickly and spreads rapidly in a controlled setting, requiring frequent pruning and management. Wisteria fits this description, as its twining, woody stems quickly cover arbors and fences.
The definition of a truly “invasive” plant is much stricter and has profound ecological implications. An invasive species is non-native to the ecosystem and, once introduced, spreads rapidly, causing environmental or economic harm. These plants lack natural predators, allowing them to form dense monocultures that displace native vegetation and fundamentally alter the habitat. Some wisteria species exhibit both aggressive growth in gardens and destructive invasive behavior in the wild.
The Species in Question: Identifying Invasive Wisteria
The two main species responsible for the invasive reputation are the non-native imports: Wisteria sinensis (Chinese Wisteria) and Wisteria floribunda (Japanese Wisteria). Both were introduced to North America in the 1800s as ornamental plants, but they have since escaped cultivation. They are now recognized as serious threats because they climb high into the forest canopy, shading out and structurally girdling native trees with their powerful stems.
To distinguish the invasive species, observe the direction of their vine twist and the length of the flower clusters (racemes). Chinese Wisteria (W. sinensis) twines counter-clockwise and produces racemes six to eight inches long. Japanese Wisteria (W. floribunda) twines clockwise and is known for clusters often exceeding one foot in length. Chinese Wisteria generally blooms earlier, often before its leaves fully emerge, while Japanese Wisteria flowers slightly later.
The invasive species can be identified after flowering by their velvety, fuzzy seed pods. In contrast, the native Wisteria frutescens (American Wisteria) is not invasive. It blooms much later in the season (June or July), produces shorter flower clusters, and develops smooth, hairless seed pods.
Controlling Established Invasive Plants
Effective control of established invasive wisteria requires persistence and a combination of physical and chemical methods. The plant possesses a massive, deep root system that readily re-sprouts. Simply cutting the vines back is insufficient; this aggressive pruning only encourages the plant to send up multiple new shoots from the root crown. The most effective strategy is the cut-stump method, which targets the root system directly.
The cut-stump process involves cutting the main vine stem as close to the ground as possible, ideally within two inches. Immediately apply a concentrated, systemic herbicide, such as a 25% solution of glyphosate or triclopyr. This solution is painted directly onto the fresh-cut surface of the stump. This immediate application ensures the herbicide is translocated down to the roots before the plant seals the wound.
For mature vines with thick, woody bark, a basal bark treatment can be used. This involves applying an oil-soluble herbicide, such as triclopyr ester, mixed with a penetrating basal oil. This mixture is sprayed around the circumference of the lower 12 to 15 inches of the stem, allowing the chemical to penetrate the bark. Regardless of the method used, follow-up monitoring and treatment of new sprouts are necessary for two to three years to ensure complete eradication.
Native and Non-Invasive Alternatives
Gardeners who appreciate the look of wisteria but want to avoid the ecological risks have excellent non-invasive alternatives. The most suitable choice is the native American Wisteria (Wisteria frutescens), or its cultivar, Kentucky Wisteria (Wisteria macrostachya). These native versions are less vigorous, less aggressive, and grow to a more manageable size. The native species still produces beautiful, fragrant flowers but without the rampant growth and ability to choke out native trees.
Other excellent native vines offer similar ornamental value. Coral Honeysuckle (Lonicera sempervirens) is a vigorous climber with tubular red-orange flowers that attract hummingbirds. Virginia Creeper (Parthenocissus quinquefolia) is another native option prized for its ability to cover large areas and its spectacular red fall foliage.