Ever since I was a kid, the Wisteria plant was one that I wanted to have in my yard. However, I had heard rumors that these plants had a penchant for killing other vegetation nearby. I did some research and wrote this post to get to the bottom of the issue.
Wisteria will kill other plants because it’s an aggressive grower that will compete for sunlight, space, and nutrients. Whether you plant it near a tree or other plants, the wisteria vines will grow and suffocate them. You can control the wisteria by pruning or killing it.
Does Wisteria Kill Other Plants?
To understand how Wisterias affect other plants, you have to look into how they grow.
All About Wisteria
If you try to grow Wisteria from seed, prepare for decades of care before you see any blooms. From seed, it can take up to 20 years to bloom.
That’s why most of the plants you see flourishing come from cuttings. It’s one of the best ways to grow the plant. But even then, it can take years of dedication to successfully grow these plants.
There are several types of Wisteria out there. But the two main varieties you’ll see in the gardens are Chinese Wisteria and Japanese Wisteria.
Therein lies the problem with this plant.
How Wisteria Kills Plants
As the plant grows, it needs a sturdy structure for support. Many will use a fence or trellis system.
Even in those situations, the Wisteria will spread. They will compete with other plants for sunlight and space. In most cases, the Wisteria will win and deprive any plant in its way of valuable sunlight. Thus, most plants in the Wisteria’s growth path die.
Another way that gardeners support Wisteria vines is with an existing tree. Think of it as a living support system. Unfortunately, this can cause some issues, too.
When you first plant the Wisteria, it dwarfs the living support. However, it can quickly overtake and strangle a tree you allow it to grow on. The vines will wrap around thin branches and even trunks. Eventually, they will girdle the tree and kill it.
How to Control Wisteria Growth
If you don’t want your Wisteria overtaking your yard, growth management is a must. Controlling the plant can also help you enjoy healthier blooms. There are a couple of ways to manage this plant.
Pruning is an essential task if you own a Wisteria plant. In most cases, these plants will use the previous year’s growth to develop new flowers.
By pruning the plant annually, you can keep those vines at a manageable size. Plus, it will ensure that the drooping flowers are closer to the ground for you to enjoy.
Ideally, you should prune the plant twice a year. The first will occur in the summertime. Do this about two months after the plant starts flowering. By this point, most of the flowers will fade. It’s the perfect time to start stunting the plant’s growth.
Trim back overgrown shoots. This will clean up the plant and make it more compact. The Wisteria will continue to grow a bit, but this summertime prune is important. It focuses the plant’s energy on stem strength rather that length.
During the winter, you’ll need to do a more severe pruning job. The goal here is to trim the shoots down to 3 or 5 buds. Doing this will direct the plant’s energy next year to develop more flowers.
This prune will often involve cutting 6 to 8 inches of stem off. Don’t worry. The plant can take it.
Training the Plant into a Tree
Here’s a more advanced growth management technique. With some encouragement, this vining plant can grow into a full-fledged tree.
This process can take years. But if you’re successful, it results in a self-supporting tree with stunning looks.
Start by driving a sturdy 4×4 post into the ground. The post should be at least a foot into the ground for adequate support. Up top, the post needs to be about a foot taller than the desired height of your tree.
As your plant grows, select the strongest vine to become the trunk. Trim off any side shoots about a quarter-inch above the fusion point. Then, secure this vine to the post with cloth ties.
Continue to prune side shoots as the plant grows. Allow this single vine to grow up the post. By removing side shoots, you’re directing the plant to focus its energy on strengthening the single vine.
Once it has reached the desired height, you can allow lateral shoots to flourish. By this point, the “trunk” will be thick and fully capable of supporting future growth.
How Do You Kill Wisteria?
If your Wisteria is doing too much damage to other plants, you can kill it. However, this is surprisingly difficult. Wisteria plants are very hardy and can continue growing well after cutting it down.
Start by removing most of the plant. Get rid of all vines and offshoots until you have a single plant stump. Make sure to bag everything up. If you just toss the vines in your compost pile, you could end up with a brand-new plant.
Next, you’ll need to address the stump and root system. Wisteria plants have expansive roots. They spread out quite far to create an anchor for the long vines.
You can try digging them out. But, that effort will be fruitless if you have a large established plant. Your best option would be to kill the stump internally.
To do this, you’ll need a strong herbicide. Use a product with picloram, triclopyr, glyphosate, imazapyr, or clopyralid. Those chemicals are effective at killing this powerful plant.
Mix your herbicide and aim for a strength of about 15 to 20 percent.
To ensure that the herbicide penetrates the plant, make some horizontal cuts on the stump. Peel back the bark by about an inch. The more exposure, the better.
Now, use a paintbrush to apply the herbicide. Apply a liberal coat but exercise caution and avoid getting it on surrounding plants.
The herbicide will absorb in about 24 hours. Keep an eye on the stump. If you see any new sprouts popping up, apply another coat of herbicide.
Once the stump is dead, you can cut it flush with the ground or pull it out.
Are Wisteria Toxic to Pets and Humans?
Despite the beauty of the Wisteria plant, it can be dangerous to both humans and pets. All parts of the plant are toxic. However, there are higher concentrations of dangerous compounds in the seed pods.
The plant produces seeds in hanging pods. They take on a velvety texture. Inside, the beans look like beans. As a result, they can be attractive to pets and animals.
The seeds and pods contain high amounts of lectin.
Lectin is a naturally occurring protein. Some lectins are perfectly safe. In fact, there are lectins in almost every food you eat. However, some types of lectins are poisonous when consumed in large doses.
Wisterias happen to have the toxic kind. They also have the toxic glycoside wisterin. Wisterin is in the seeds, pods, and bark of the plant.
For humans, ingesting parts of the Wisteria plant can lead to headaches, confusion, and even internal bleeding. Similar symptoms can occur in dogs, too.
Usually, symptoms are minor if with small amounts. You or your dog might experience mild to severe digestive troubles. Though, serious cases can happen. They will require immediate medical intervention.
If you decide to grow Wisteria, make sure that you keep a watchful eye over children and pets.