Gardening: Wisterias gone wild (and how to prevent it)

McClatchy-Tribune News ServiceApril 10, 2014 

In early spring a massive wisteria in California is so large it’s considered among the great horticultural wonders of the world. This single vine that now shades an acre of ground in Sierra Madre was planted from a one gallon sized seedling a century ago. Today the Guinness Book of World Records lists it as the largest flowering plant in the world.

This California plant is one of the exotic Asian species, but there also is a lovely native American species, Wisteria frutescens, from the Southeastern states. Problems begin when exotic wisteria escapes to naturalize in wild lands. It’s causing serious problems in the Southeast because they share the same preferences as our native species. Escaped Asian wisterias are listed as potentially invasive in 19 Eastern states, primarily those in the Southeast where abundant summer rain keeps every seedling growing vigorously all season long.

Though we all love wisteria, think twice before planting because exotic wisteria have escaped to infest valuable wild lands which support old growth forests and protected native species. When vines escape, they can cause unique damage to native plant communities and the wildlife they support.

Sometimes invasive plants actually evolve once they’re naturalized in wild lands, a fact which can turn a moderate problem to a severe one over time. It’s because all plants are programmed to adapt to changing climate and conditions through natural selection. Wisteria gone wild involve two exotic species, the Japanese ( Wisteria floribunda) and Chinese species ( Wisteria sinensis). In the Southeast, species have cross pollinated, which results in naturally occurring hybrids that exhibit new genetic characteristics. If that characteristic allows offspring to survive on less rainfall, exotic wisteria can move further west into arid regions of Texas and beyond.

Wisteria runners can reach 60 feet or more in length, which easily climb into shrubs and treetops. When vine cloaks the entire canopy of a tree, it shades out the foliage to interfere with photosynthesis crucial to plant life. Wisteria becomes so large it can destroy centuries old trees, often great oaks, tulip poplar, beach, pine and elm. The sheer weight of large vines is enough to pull down old growth trees after periods of heavy rain or high winds.

Wisteria is well known for spiraling around an arbor or porch post. When they twine around a tree trunk, the pressure eventually cuts through the host tree bark to girdle and kill it. Then after the tree falls, it leaves a gap in the forest canopy. This exposes thousands of wisteria seeds to sun, which accumulated over years beneath the parent plant. They sprout to become a thicket of young vines impenetrable to both humans and wildlife.

There’s another way that wisteria can reproduce to further its domain. Runners that contact earth strike roots at each leaf node. This is a process called layering, used in propagation of vines. A single wisteria gone wild can use this method to dominate several acres of ground.

For a more environmentally sensitive alternative, try our well behaved native, Wisteria frutescens, that will never become a problem. For even more options and color, try other American native vines such as try trumpet creeper ( Campsis radicans), coral honeysuckle ( Lonicera sempervirens) or Carolina jessamine ( Gelsemium sempervirens). These lovely natives will ask for little water or care no matter where they grow. Best of all, they won’t run wild, grow as big as a house, or strangle native plant communities when they decide to naturalize in America.

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