This story was originally published in May 2021.
Japanese knotweed is one of the most invasive plant species in the state, as it outcompetes many other native plant species. But it’s a delicious edible plant — and foraging for it will help you to do your part in managing this scourge on Maine’s environment while also enjoying a fresh meal.
Though it looks like bamboo, it is actually a perennial species more closely related to buckwheat that spreads vigorously through rhizomes.
Alexandria Goodwin said that she started foraging Japanese knotweed with her daughters in the Sebago Lakes region last year. She said that Japanese knotweed has a “bittersweet” taste. In fact, she notes, the species is sometimes known as the “poor man’s rhubarb.”
Abigail LeBlanc, a forager based in Bangor, said that she thinks it has more of a “lemony flavor profile.”
“I use them in all my baking recipes that allow for tart fruits,” LeBlanc said. “I’ve used a mandolin to thinly slice raw knotweed into salads for added acidity.”
The roots of Japanese knotweed also have purported health benefits, according to herbalists and natural medicine experts, including preventing and treating cognitive disorders, improving cardiovascular health, strengthening the immune system and even treating Lyme disease.
There is a scientific basis for it, too. In a 2020 study published in Frontiers in Medicine, researchers from the Johns Hopkins Bloomberg School of Public Health, with colleagues at the California Center for Functional Medicine and Focus Health, surveyed the ability of 14 plant-based extracts to kill Borrelia burgdorferi, the bacterium that causes Lyme’s disease, compared with two common Lyme antibiotics. Japanese knotweed was one of the top performers in killing microcolonies of the bacteria.
Molly Zerg Anderson in Hampden said that she has been foraging for Japanese knotweed for about four years in order to help manage her Lyme disease symptoms.
“The roots of knotweed contain some of the highest amounts of resveratrol in a plant in the world, to my understanding, and resveratrol is a very effective herbal antibiotic for Lyme,” she said.”
There is controversy about Japanese knotweed’s medicinal properties in the foraging world, though.
“I think that it’s not the best way to go,” said David Spahr, author of “Edible and Medicinal Mushrooms of New England and Eastern Canada,” who is based in Washington, Maine. “If you wanted to take it and know how much you’re getting, you could buy it [in pill form] at Walmart. You’ll get fewer ticks on you in the drug store. The whole resveratrol thing starts giving the plant an excuse for its existence. We can’t be giving that plant any excuses.”
Finding a patch
To harvest Japanese knotweed, you first have to find it.
Japanese knotweed grows along roadsides, stream sides and near the foundations of old buildings, according to Waldo-based Tom Seymour, naturalist and author of “Wild Plants of Maine — A Useful Guide, Forager’s Notebook, Foraging New England.”
However, you want to be cautious about where you harvest Japanese knotweed.
“You won’t find it deep in the woods so you’ll need to source a patch that hasn’t [been] treated with herbicide or been exposed to exhaust [or] salt from the road way,” LeBlanc said.
Anna Christina, herbalist and owner of Mana Medicinals in Boothbay Harbor, said that she will do a “background check” of her harvest sites.
“I make sure any time I’m going to harvest on somebody’s property [that] there’s no septic run off, if they do any spraying on the property make sure their neighbors don’t spray,” Christina said.
Once you have found a suitable patch, you have to make sure that the Japanese knotweed is prime for harvesting.
“You want [shoots] that are typically no taller than 12 to 18 inches because beyond that they can start to get woody like asparagus,” Goodwin said. “We tend to take the stalks that are as big around as a dime to maybe quarter size, as our family doesn’t eat them whole.”
Timing matters if you are harvesting the roots for medicinal purposes, too.
“It’s best to harvest [the roots] when [the plant] is young and not just when it’s first growing but also the new shoots because you want the smaller roots of it,” Christina said. “The older roots are a lot woodier. The smaller roots have more potent medicinal properties. I look for the very skinny and small shoots.”
Though Japanese knotweed is best harvested in the early spring — Spahr said that he usually harvests the first two weeks of May — not all the shoots will come up at the same time. Spahr said to check in shaded areas for tender young shoots popping up a little later.
“It can always be ‘knotweed season’ though because if you cut it down at any point of the growing season it will promptly send up new shoots,” Anderson said.
Spahr said that young Japanese knotweed shoots look like “pink asparagus spears.” Seymour said to bend a stalk and if it breaks easily and cleanly, with a soft “pop,” it is still good.
If you just plan on eating Japanese knotweed shoots, you can simply snap the young tender shots off. If you are looking to harvest Japanese knotweed for medicinal purposes, though, you will want to get the roots.
“I use a shovel,” Christina said. “[The root] can go horizontal as well so when I dig down, I try to get as deep as I can and then slowly pull it up. I put my hands in the soil and try to pull the root up underneath because the roots will easily just break off and then you’ll lose it.”
Because the plant is invasive, many of the rules for ethical foraging are more flexible. Per usual, you must have permission to forage on the land, but you can gather a bit more than you would for, say, fiddleheads.
“You needn’t leave any knotweed for future foragers because it is so widespread and common,” Seymour said. “Also, it grows rapidly and harvesting cannot set it back. Take all you can use.”
You also have to be careful about how you transport your foraged Japanese knotweed.
“Transfer the plant from point A to point B like you’re transporting a bloodborne pathogen,” LeBlanc said. “I pick the shoots and throw them in a plastic bag and the only time they see oxygen again is when they’re in my kitchen to be washed and prepped.”
Spahr added that he wouldn’t toss unused Japanese knotweed in his compost pile or even in the trash.
“You don’t know where that trash is going to go,” he said.
How to use Japanese knotweed
Clockwise from left: Steamed Japanese knotweed (photo courtesy of Fia Fourtne), a Japanese knotweed tincture (photo courtesy of Anna Christina) and Japanese knotweed tartlets (photo courtesy of Molly Zerg Anderson).
Once you have your harvested Japanese knotweed, you can use it in many ways.
First, you can use the shoots of the plant in the kitchen. Seymour said that he will steam his Japanese knotweed like asparagus.
“The thinner shoots are great grilled or fried, eaten similarly to asparagus,” Goodwin said. “The tops are often munched on raw. We chop up our thicker shoots, which have a big hollow center just like bamboo, and then make pie, crisp, jam, fruit leather and freeze it raw.”
Anderson said that she will use Japanese knotweed the same way as rhubarb in tarts, pies or sauces. Like rhubarb, you can also freeze Japanese knotweed to use for later. Seymour said that he will blanch it before freezing. LeBlanc and Anderson said that they will just toss the raw Japanese knotweed in the freezer and it keeps equally well.
The roots can be used for medicinal purposes. To make a Japanese knotweed tincture, Christina said that she will steep the chopped and macerated roots in warm water for an hour or two, then put the solution with a high-proof organic grain alcohol in a half-gallon mason jar and shake it every day for a few weeks.
“After the three weeks, I let it sit for three months at least,” Christina said. “The longer you let it steep, the more medicinal properties you’re going to get from it. After it’s all tinctured then I strain it through a thin mesh strainer and cheesecloth to get all the particles out.”
Christina said that taking the tincture “depends on the person and their size and weight,” but normally she will recommend a quarter of a dropper full a couple times a day.
“You want to just take it in moderation,” Christina said. “Just like with anything, you don’t want to just take so much of something because you hear it’s good for you. With any kind of herbal medicine, just like medication or food, you want to start slowly and see how your body reacts.”