Wisteria, particularly the highly aggressive and invasive Asian varieties, can definitively kill trees. This fast-growing, woody perennial vine utilizes trees for structural support to reach sunlight. Its vigorous growth and woody nature allow it to harm host trees through two primary methods: mechanical damage from constriction and long-term ecological competition. The vine’s ability to quickly establish itself and its impressive longevity make it a significant threat to mature trees in forested and suburban environments.
Physical Damage Through Constriction
The most direct way wisteria harms a tree is through a process known as girdling. As the vine grows, its woody stem tightly wraps around the host tree’s trunk and supporting branches. The expanding vine acts like a tourniquet, applying immense pressure to the tree’s outer layers.
This pressure compresses the cambium layer, which produces the tree’s vascular tissues. The cambium produces the xylem, which transports water and nutrients up from the roots, and the phloem, which moves sugars produced during photosynthesis down to the roots. By crushing these delicate tissues, the vine effectively cuts off the tree’s internal circulation system. When the phloem is damaged, the roots starve because they cannot receive sugars from the leaves, and damage to the xylem prevents water from reaching the canopy. This mechanical strangulation leads to the tree’s death.
Ecological Harm Through Competition
Beyond the physical throttling of the trunk, wisteria causes significant harm by competing for sunlight and essential resources. The vine’s natural climbing habit is driven by its need to reach the highest point of the canopy to maximize sun exposure. Once it reaches the top, the wisteria spreads its dense, leafy foliage outward, creating a thick blanket over the host tree’s crown.
This canopy coverage effectively shades the host tree’s own leaves, significantly reducing its ability to perform photosynthesis. Over time, the host tree’s growth slows, its branches weaken, and its overall vigor declines under the perpetual shade.
Furthermore, the sheer biomass and weight of the mature wisteria vine introduce a structural risk to the tree. A large, well-established vine can add hundreds of pounds of weight, especially when saturated with rain or covered in ice and snow, placing considerable stress on the host tree’s limbs and leading to catastrophic structural failure during strong winds or storms.
Identifying Aggressive Wisteria Species
It is important to distinguish between the highly invasive species and the less aggressive native alternative. The two most problematic species are the Chinese wisteria (Wisteria sinensis) and the Japanese wisteria (Wisteria floribunda), which possess a far more vigorous growth habit. The native American wisteria (Wisteria frutescens) is significantly less aggressive and rarely poses a threat to mature trees.
A key identification feature is the direction the vine twists around its support: Chinese wisteria twists in a counter-clockwise direction, while Japanese wisteria twists clockwise. The flowering characteristics offer a clearer distinction, particularly the timing and size of the blooms.
The invasive Chinese and Japanese species typically flower before or just as their leaves emerge in spring, producing long, pendulous flower clusters that can reach up to a foot in length. The native American wisteria blooms later, well after the leaves have fully emerged, and its flower clusters are noticeably shorter and more compact, averaging three to six inches long.
Safe Removal and Management Strategies
Safely removing wisteria requires a two-step approach. The first step involves severing the vine at the base of the tree trunk at a comfortable working height, typically around chest level, using a saw or loppers. This cut should completely encircle the tree to ensure the vine is entirely disconnected from its root system.
Crucially, the portion of the vine remaining up in the tree’s canopy must be left in place to die and decompose naturally. Attempting to pull the heavy, entwined vine down can cause severe damage to the host tree’s bark, tear off limbs, or even pull down the canopy itself.
The second step is to prevent the vine from re-sprouting from the root collar. Immediately after cutting, a concentrated systemic herbicide, such as glyphosate or triclopyr, should be applied directly to the fresh cut surface of the remaining stump. This stump treatment allows the herbicide to be drawn down into the root system, killing the entire plant without harming the surrounding vegetation or the host tree.