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10/01/2020 12:01 AM

Weed Vigilantes Put Invasive Knotweed on a Starvation Diet

Suzanne Thompson of Old Lyme shows one of the key tools in defeating Japanese knotweed: the black plastic bag. “Knotweed must be bagged and incinerated,” she says. Even tiny pieces left on the ground can re-sprout in short time.Photo courtesy of Suzanne Thompson

Suzanne Thompson didn’t wake up on the first day of 2020 thinking about Japanese knotweed. But, after all, it is 2020—and stranger things have happened than the turn Thompson took in May of this year. She founded a local group to strike back at this awful plant, which is sometimes called Mexican bamboo, though it is neither Mexican nor bamboo.

The all-volunteer campaign was started to spread the word about an effective, chemical-free way to get rid of Japanese Knotweed and to reestablish native ecosystems, says Thompson. “We don’t spray it. We cut it.” Then she adds, “We starve it.”

In the horticultural world, the technique Thompson describes is sometimes called “carbohydrate deprivation.” The theory behind it is simple: Deprive a plant of its leaves and you deprive it of photosynthesis, the source of its food. The method works quickly on annual plants, and much more slowly on tough, mega-rooted plants like Japanese knotweed (JK).

“It’s a very simple process, but there are a few nuances you can’t ignore. And it does take some time, commitment, and patience,” she says.

Thompson is no stranger to horticulture and environmental issues. She’s a regional nature writer and radio broadcaster, an active member of the Duck River Garden Club in Old Lyme, and outreach coordinator for Save Oswegatchie Hills in East Lyme.

No wonder JK caught her eye.

“The past few years, I’ve been driving my kids to and from soccer practice and dance classes, watching the stuff grow inches by the day along Route 156 in Old Lyme,” she says. “I kept thinking, ‘I should stop and cut it down.’ But I never had the time.”

Then 2020 happened, and, as happened to so many of us, Thompson’s daily routine was involuntarily rearranged.

Thompson was aware of the work done by Petie Reed and Abby Stokes, who tested the cutting method in the Pine Grove community of East Lyme. Their results were so successful they presented their findings at the Connecticut Invasive Plant Working Group 2016 Symposium. (They will present again at the 2020 Symposium on Wednesday, Oct. 7. For more information, visit

Thompson also took inspiration from the popular Pollinator Pathway (, a successful grass-roots movement to dedicate a portion of a yard or open space to pollinator support.

What’s so bad about knotweed?

This invasive plant (called Reynoutria japonica in the botanical world) takes root on riverbanks, hillsides, yards, roadsides, and almost anywhere there’s a bit of sun and moisture. In the U.K., knotweed has been declared the most pernicious weed in the country. It is so pervasive in some areas, and it can undermine building foundations and stop the sale of real estate.

“Here in the U.S., it is crowding out our native species,” says Thompson. “And it takes up the spaces that are needed to support our birds, butterflies, other pollinators and wildlife.”

Knotweed spreads aggressively through roots and runners.

“That’s why it is not enough to cut and run,” says Thompson.

The cuttings must be bagged and incinerated.

“The cuttings sprout prolifically,” she emphasizes, “like the brooms in the old Sorcerer’s Apprentice animation. If you mow or weed whack JK, you’re only spreading it more, not stopping it,” she says.

The plant also spreads through seeds.

Thompson concludes, “This is the classic invasive species that thrives and spreads here because there aren’t any natural predators to keep it in check. Deer won’t even eat it.”

Since May, Thompson posts events to Facebook groups such as Women of Old Lyme and Lyme, the Connecticut Land Conservation Council, Master Gardeners Association, etc. There’s also a two-page flyer that Facebook visitors can download.

“We had two pilot projects this summer,” says Thompson. “One behind the Old Lyme Town Hall, and a second at the Lyme Art Association.”

She acknowledges Suzie Bolduc of the Duck River Garden Club for “single-handedly adopting the LAA space.”

And next year?

“The goal is to expand next year, recruit more volunteers, and tackle more knotweed patches,” she says.

Reach Suzanne Thompson at

Kathy Connolly is an Old Saybrook landscape designer who writes and speaks on landscape ecology and horticulture. Contact her through

In the fall, it is easy to recognize Japanese knotweed by its tall stalks and prolific flowers. Photo from Wikimedia commons, CC 1.0
A small piece of Japanese knotweed re-sprouts easily on bare soil. Pieces must be removed after cutting.Photo courtesy of Kathy Connolly