Once you know what to look for, it seems like they’re everywhere, coming for people’s backyards and gardens, and they can’t be killed by normal means.
Lydia Casey, with her knife, jug of herbicide and Q-tip swabs, is trying to fight the menace’s spread, one black locust tree at a time.
Black locust trees are a tenacious, hard-to-kill plant and invasive weed in Southwest Washington, and in Casey’s experience, most people don’t know what they’re dealing with until they’re near-overrun.
Casey, a master gardener, has made it a small personal crusade around her Andresen-St. Johns neighborhood to root out black locust.
Battling black locust
In young black locust trees, the bark is smooth and green. In older trees, it's brown and deeply furrowed.
The plant's seedlings and sprouts have long paired thorns at the base of each row of leaf stems. The plant's leaves alternate along stems and are composed of seven to 21 smaller, oval-shaped leaf segments, or leaflets.
Its fruit pods look like pea pods with brown, leathery skin and hold about four to eight seeds. Its flowers bloom in drooping clusters in May and June.
It's irritating, but black locust isn't one of the county's higher weed management priorities, said Mike Monfort, the lead field inspector for Clark County Vegetation Management.
The county will do preemptive work to slash black locust for road rights-of-way or construction projects, but the county doesn't mandate controls like it does for other weeds. For homeowners, he said, the county's efforts are geared more toward education or offering on-site advice.
He said his office won't usually give specific care advice over the phone, but the staff are happy to go out to homes and offer advice. The extension office and its master gardeners program also provide guidance.
There are several resources that county landowners grappling with black locust trees or other unwanted plants can contact:
- WSU Extension Clark County: 360-397-6060.
- Clark County Vegetation Management: 360-397-6140.
- Vancouver Urban Forestry: 360-487-8308.
Homeowners can usually handle smaller black locust plants on their own. When they get tree-size, it gets complicated. And expensive.
The Vancouver Watersheds Alliance offers grant help that can be used to help defray costs for cutting down nuisance trees in Vancouver. It can be contacted at 360-852-9189.
Charles Brun, horticulture adviser with the extension service, said he's heard of people working with live edge furniture builders to remove offending black locust trees as a way to reduce costs.
The wood makes for quality hardwood, and some furniture builders will pay to cut down and remove the tree. Some landscapers will also pay for the value of the hardwood.
Brun recommended people who try that route still work with an arborist or other professional to ensure the stump and root are properly treated, to prevent new sprouts.
When dealing with trees, Brun also recommended contacting the county or appropriate city department before getting out the chain saw, because there may be legal issues to address before taking out a tree.
— Andy Matarrese
Once she learned about it several months ago, she said she started seeing it all over.
She works house to house helping neighbors control their black locust. Many of them, she said, didn’t know what this pesky weed was until they reached out to her.
“I’ve talked to everybody and their brother, and when they see it, they call me,” she said.
“You can’t just cut it down,” she said. “Cut it down and you’ll get 15 more.”
Beyond the young plants’ thorny shoots, part of what makes locust such a nasty weed is its growth potential, said Erika Johnson, the Clark County Washington State University Extension’s Master Gardener program coordinator.
Like tree of heaven plants, another local pest tree, black locust tends to pop up unexpectedly, she said.
They have a habit of being the first plant in a cleared area, and they can crowd out other plants, compounding the problem, Johnson said.
Charles Brun, horticulture adviser with the extension service, said he doesn’t think there are more growing now than have previously. Still, he said, once you know what to look for, you’ll start seeing it everywhere.
“I’ve seen entire neighborhoods be taken over by these trees,” he said.
They grow from seeds and sprout from underground shoots, and spread fast.
Damaging the tree, mature or young, just puts it into survival mode, prompting it to send up new sprouts from the root system or stump.
When people call the county’s vegetation management office about black locust, they’re often asking for help after failing to fight it off on their own, wondering how one “dead” plant turned into eight, said Mike Monfort, the office’s lead field inspector.
If any root retains a flicker of life, he said, the plant can grow back, and that’s why almost any practical management plan will likely require some herbicides.
“It’s a challenge. That’s a kind way of putting it,” Monfort said.
Once a landowner finds black locust, it’s better to act sooner than later, Brun said. They grow fast. In less than two months, a locust can grow to a bush more than 6 feet tall with inch-long thorns.
“As soon as you see them, start to consider some kind of management program. If you simply cut them they’re going to resprout, and then they’re going to spread,” he said.
Brun said landowners need to apply a proper herbicide — they don’t come as sprays; it’s poured or brushed on — to the plant stump within 30 minutes of cutting.
When they get to full tree size, he said, another strategy is to girdle the tree: Take a hatchet and cut a ring around the bole of the tree.
That should allow the tree to die where it stands and prevent further sprouts, he said, but it might still need herbicides. Even with all of that, it might take a few years for the plants to die off.
Brun strongly encourages landowners to talk to a landscaping expert before tackling larger locust problems, especially fully grown trees.
The trees aren’t all bad. They’re on the city of Vancouver’s list for invasive trees with the trees of heaven, but they aren’t actually on any state or county lists as official noxious weeds, Monfort said.
The trees are native to North America, but toward the Southeast.
When fully grown, the trees can reach heights of 100 feet, and plenty of people find them quite likable.
One black locust planted more than a century ago outside of Mill Plain Elementary was named a Vancouver Heritage Tree in 2000.
“They’re not unattractive,” Johnson said, but she added any tree in one person’s yard will quickly become a tree in all his neighbors’ yards.
For now, Casey has been logging where she finds the plants and testing different management strategies to find what works best.
She’s been going around her neighborhood and to local churches handing out fliers about the plant printed by the extension service.
Gardeners all over the county have probably been seeing this little plant, and, thinking it was just another weed, simply cut it or pulled it out without knowing they’ve just aggravated it, she said; she’s probably done it herself.
“That’s the problem. I didn’t know I needed to know all these things,” she said.
She hopes getting the word out will help keep gardeners from being overrun.
“I’m doing the best I can to fight for my neighbors,” she said.
