What a beautiful plant!
For a couple of weeks in the spring we see vast displays of dramatic purple blossoms cascading from vines that can cover an entire block in some locations. It is a surprise and a delight to see these displays of color, climbing high into the trees that give them support and access to sunlight. The vine twists counter-clockwise and the flowers appear in April or May. What is that gorgeous, showy purple bloom?
It is Wisteria sinensis, or Chinese wisteria. Bill Bryson, in his delightful book, “A Short History of Nearly Everything,” shares tales of gentlemen of learning, botanists, naturalists, and adventurers who spent years and fortunes in the eighteenth century seeking glory and wealth by introducing new species, “horticultural novelties,” to England and America. Thomas Nuttall walked back and forth across the U.S. collecting growing things never before seen. The stunning wisteria was brought to the U.S. in 1816 for use as an ornamental plant. It is Nuttall who named the vine after Caspar Wistar, the leading U.S. anatomist at that time. Poor Wistar is also remembered for having failed to recognize the significance of a huge thighbone unearthed in New Jersey that would later introduce the dinosaur to science, but his name lives on in this plant that is sometimes pronounced wistaria, especially in England. Other spellings include westaria and wysteria.
But It Is a Problem.
On the other hand, the climbing vines of wild wisteria are a non-native species that, like the cartoons of Pinky and the Brain, want “to take over the world.” If left to continue to grow, they can eventually kill the trees by girdling and crushing them, and leaving the tangle of vines interwoven into a mat that is almost impossible to tame. Gardener Anna Sheets moved from New Mexico to the South. “The first spring, it was magical.” Now, she says, “I keep my pruners sharp, nearby and unashamedly cut off any vine I see.” Perhaps you had a similar reaction your first spring in Wake County.
Wisteria destroys wooden structures, too. It finds any gaps or cracks and works its way under siding. Eventually it can tear down whole buildings. Sometimes when the leaves are off the trees, you can see sad relics of early homes reclaimed by Mother Nature.
The non-native wisteria vines, by 2016, were reported as invasive in at least 27 states and the District of Columbia, from Massachusetts to the Midwest and south to Texas. The vine forms a thicket and deprives other plants of the light and nutrients they need. It spreads by rooting at each node and also sends up stems, called stolons, above the ground. After the bloom, the seeds develop in velvety bean pods that pop open when they dry, sending the seeds flying in the fall.
The vine can live half a century, crowding out native plants and trees. It can grow to be 70 feet tall, depending upon the height of the tree or structure it climbs. In a process called circumnutation, it develops a pattern that resembles a helix which then tightens until it cuts through the bark and strangles its host, just like a boa constrictor strangling its prey. As if that were not enough, wisteria is toxic to humans and also to pets. It contains the chemical wisterin which, if ingested, can cause “wisteria syndrome,” lasting up to a week. Symptoms may include dizziness, confusion, delirium, incoherent speech, headache, vomiting, sweating, and diarrhea. Don’t eat those beans!
I’ll bet you didn’t know about National Invasive Species Awareness Week. It lasts seven days from the last Monday in February. In 2024, that was February 27 to March 5. Clever articles warning of the threat it poses are titled “Wisteria: Criteria for Deliria?!” and “Wisteria hysteria: Flowering vine grows wild in South.” The state of Maryland named both Chinese and Japanese wisteria (Wisteria florabunda, which ascends clockwise) “Invaders of the Month” some time back. Such a dubious honor.
Can You Kill the Beast?
If you are itching to do battle, you must be very determined; it will always try to come back. The roots, seeds, and vines must all be eliminated. The first time you cut off the vines, some roots will remain. Be vigilant and watch for new shoots. Get rid of each and every one. Check for new growth regularly. Heavy pruning will be necessary, and do wear gloves. Herbicides will help.
Use commercial chemicals or, if you prefer, try home remedies such as bleach or salts. The cut vine will immediately begin to heal itself, so you need to apply the herbicide right away, covering the cut end so the chemicals don’t wash away in the rain. Vines climbing up trees need two cuts to remove a section completely. The vine is tough; it can stand cold, shade, and periods of dry soil.
Meanwhile, Across the Pond…
At the beginning of the new millennium, I attended a wedding at Hatfield House, an estate in Hertfordshire, England, completed in 1611. It was a fairytale wedding in a palatial setting, made very traditional by the purple wisteria blooms festooning the walls and arches.
In 2023, I spent most of September in England and saw the vines and foliage in general usage adorning the Edwardian homes in a posh suburb of London. I verified it is the same varieties, Chinese and Japanese, that plague us here. How can that be? Not only is it under control, but an article by Louise Gray in the Telegraph a few years ago stated that Britain’s wisteria “is under threat from an Asian insect capable of wiping out swathes of the beautiful climbing plant.” The warning came from none other than The Royal Horticultural Society.
Well, the southeastern areas of the U.S. have ideal growing conditions for this plant, and it thrives in many areas left wild. England, on the other hand, is rigidly zoned for fields, woods, homes, and commercial use. It is an island with limited space. The gardens are groomed with pride. English ivy also adorns their historic buildings, though the same ivy is another invasive species here. The plants are faithfully pruned to desired areas and structures. The English love their wisteria, and there are even wisteria walks in London.
A Heritage of Love
There are, however, other cultivated varieties that you can train to make a beautiful cascade of blooms without being overrun in the process. We used to drive our neighbor, Helen, to her cancer treatments in Chapel Hill. She was from England, where wisteria and ivy are both trained to cover ancient walls without destroying them. Her home had wisteria that was lovely, so I asked her for cuttings, wanting to memorialize her with something beautiful that I knew she loved. Alas, as hardy as the wild wisteria has become, the plants can be finicky. My cuttings died.
Our childhood home in Maryland had wisteria trained along the screened porch. I don’t know if Mother planted it, or if Dad had to keep it pruned, or if it was a variety that doesn’t get out of hand so easily.
American Wisteria
From an online site called “Gardening Know How,” I was relieved to read about American wisteria, Wisteria frutescens. It is a blue-flowered cousin, or occasionally white, which is suitable in USDA zones 5 to 9. (We are in zone 7b.) There are online businesses that can ship it, but I also found local stores that list it as available, sometimes calling it blue wisteria. Prices listed varied from $15 to $100.
As a native plant, American wisteria grows in bottomlands in moist places, swamps, flood plains, and along rivers. It requires a nutrient-rich, damp spot in your garden. It comes with the warning that the seeds in the pods can cause extreme nausea and vomiting, because it is toxic like its cousin. It needs a support structure such as a trellis, arbor, or fence. Constant moisture will be required. You will need to do some hard pruning, but it has no major problems with diseases or insects. In fact, it hosts multiple varieties of butterflies.
Close to Home
“The Little Prince” by Antoine de St. Exupery speaks of invasive species.
In fact, on the little prince’s planet there were—as on all planets—good plants and bad plants. The good plants come from good seeds, and the bad plants come from bad seeds.
As it happens, there were terrible seeds on the little prince’s planet . . . baobab seeds. The planet’s soil was infested with them. Now if you attend to a baobab too late, you can never get rid of it again. It overgrows the whole planet. Its roots pierce right through. And if the planet is too small, and if there are too many baobabs, they make it burst into pieces.
We are not in danger of bursting. Our planet is filled with wondrous things to behold and to learn about.
Here in Wake County, there are plenty of places to find glorious thickets of purple wisteria gone wild. When my husband found it killing mature forest trees in our neighborhood common area, he set to work, pitting himself against the intrusive vine which he battled all summer. First, he cut through the base of the vines and watched the leaves at the very tops of the trees turn brown and blow away. Then he tugged on the vines to pull out the ones that would budge. Allowing for the turns around the tree trunk, the longest was about 60 feet. He traced the roots through the dirt and pulled up long runs of 15 and 20 feet. He brought home impressive sections of thick vine and twisted growth. His efforts have revealed mature trees that had been slowly strangled for decades. He can slay dragons. He’s my knight in shining armor.
