Don’t Kill All the Japanese Knotweed!

Spring 2021

By Joyce White

Japanese knotweed (Polygonum cuspidatum) has the unfortunate reputation of “invasive species” which means that there has been a concerted effort to eliminate it. In the process, we may be losing a valuable source of medicine.

Not only that but Japanese knotweed has been a food source for both human and animal foragers alike, and its tall, bamboo-like stalks make a dependable hedge. If it hasn’t been noticed before, it will surely be noticed in late summer when its profuse, lacy and fragrant flowers attract bees and other pollinators.

I first met Japanese knotweed nearly 50 years ago when my teenage son Gary took a summer course in foraging. He was still living at home so we tried out each new addition to his foraging repertoire. Until then, I hadn’t realized that the cluster of tall plant across the road that flowered in late summer was actually Japanese knotweed. It had a mild rhubarb flavor, but I liked real rhubarb better so I left knotweed for the critters. Gary did make a tolerable knotweed pie and jam, he says.          

I first heard of its medicinal possibilities, especially in treating Lyme disease, when I read Stephen Buhner’s book “Healing Lyme: Natural Prevention and Treatment of Lyme Borreliosis and Its Coinfections,” published in 2005. (An updated version is now available.) Native to Japan, Taiwan and Korea, knotweed, Buhner says, was introduced as an ornamental in 1825 to Britain and in the late 1800s to the U.S. It has naturalized in many parts of the world and is now known to be exceptionally hard to eradicate. When attacked, it responds by growing more roots.

The roots (rhizomes) of this 3-to-9-foot plant can be collected in early spring but fall is the preferred time to harvest. At that time, the plant’s energy has migrated to the root and can be dried for use as medicine. Buhner describes the plant as a powerful addition to the western medical pharmacopeia.

I don’t know anyone who grows it intentionally but Deb Soule at Avena Botanicals – a more than 35-year-old, reliable herbal business in Maine – orders her supply from a reputable organic grower and I order Japanese knotweed extract from Avena Botanicals. Most anyone interested in collecting a supply just has to look for it growing wild.

The many herbal actions Buhner lists for Japanese knotweed include antibacterial, antiviral, anti-spirochetal, immunostimulant, anti-inflammatory, central nervous system relaxant, brain and spinal cord protectant, anti-carcinogenic, vasodilator, cardioprotective, antithrombotic, hemostatic and astringent. (In “Healing Lyme”Buhner explains in scientific detail how knotweed acts physiologically for anyone who wants to learn more.)

Japanese knotweed has broadly systemic actions and its function in Lyme disease, Buhner says, modulates and enhances immune function. It is active against a number of gram-positive and gram-negative bacteria (so-called based on a bacteria’s response to the gram-staining method of bacterial differentiation), including the spirochetes involved in Lyme disease.

Japanese knotweed’s constituents, the author notes, cross the blood-brain barrier where they exert actions on the central nervous system, specifically protecting the brain from inflammatory damage, microbial endotoxins and bacterial infections. It can enhance blood flow especially to the eye, heart, skin and joints, making it especially helpful in Lyme disease as it facilitates blood flow in hard-to-reach areas to kill the spirochetes. It can be useful in treating the Lyme coinfections of bartonella and neuroborreliosis, Lyme arthritis and post-Lyme syndrome.

Despite at least a 2,000-year-old history of its use in Asia, Buhner notes that recent interest in its use in the western world is a result of research into the medicinal use of Japanese knotweed. He attributes this interest to its high content of resveratrol, a potent vasodilator and inhibitor of platelet aggregation. A number of other compounds may also be involved but resveratrol and trans-resveratrol seem to be the most potent. Red wine has significant amounts of these compounds, which easily move across the gastrointestinal mucosa and circulate in the bloodstream. It should be stressed, Buhner says, that while resveratrol does do amazing things by itself, it is not sufficient in treating Lyme disease. In Lyme, the whole Japanese knotweed plant is crucial because of the broad-spectrum, synergistic action of all the constituents. As a whole herb, it is much more powerful than any one constituent by itself.  

As part of its modulating and protective action on the endothelial cells lining blood vessels, Japanese knotweed, Buhner explains, stimulates the formation of new blood vessels and the healing of damaged ones in areas such as burned skin. But it also stops the development of new vessels and blood flow in areas where it should not occur as in tumor formation.

Using its Latin name, Buhner states, “Polygonum acts as an angiogenesis stimulant in a number of ailments: burns, chronic inflammations such as rheumatoid arthritis, debilitating ophthalmic disorders such as diabetic retinopathy and macular degeneration, brain disorders such as stroke and various forms of heart disease.” It may come to play an important role in the treatment of the so-called wet form of macular degeneration in which growth of abnormal blood vessels occurs in the eyes.

All this information (and a lot more) was derived from studies – 34 pages of references attest to the use of these studies – conducted before publication of “Healing Lyme” in 2005, and there is probably more information available now.

And if all those healing possibilities aren’t enough to convince people not to destroy every patch of Japanese knotweed they see, there are other uses. It can be useful in preventing erosion and can provide a hedge screen. I see it most often growing along ditches where it doesn’t appear to be doing any harm. It has a reputation of spreading and crowding out other plants, but the one I’ve watched for more than 23 years in this small town in western Maine seems not to have spread much in all those years.

After reading glowing reports from foragers, I plan to sample the new shoots from that patch come spring. Robert Henderson in “The Neighborhood Forager” declares Japanese knotweed as friendly to foragers because the fat new shoots that emerge in spring are an excellent vegetable. The new shoots resemble new asparagus shoots in appearance but not in taste. Henderson and other foragers describe its taste as tangy and rhubarb-like. He suggests cooking those new shoots in a little salted water, stock or wine with garlic and onion, and serving them hot or chilled on toast with either a cream sauce or mayonnaise. The young knotweed leaves can be cooked like any other edible greens, and are mild and tender. Their mucilaginous quality makes uncooked sprouts unpalatable – “disgusting” is Henderson’s term.

Japanese knotweed harvest. Illustration by Toki Oshima

He says knotweed “fairly leaps out of the ground in early spring, growing several inches per day.” If you notice where those tall, flowering plants are in summer and where the bare, knotty canes rattle together in winter, then you’ll know where to look for the new shoots in spring.

Foragers have only to watch the ground in late March or early April, Henderson says. Soon brick-red, fingertip-sized nubs appear at the base of the canes, quickly growing an inch or two and turning white. At this stage, the white stage, they are mildly toxic but a day or two later they reach the harvest stage. They quickly shoot up to 6 inches and double in diameter, turning green with red highlights and sticky, papery collars at the joints. A good supply of the shoots can be harvested easily with a sharp knife when sprouting is in full swing. At this point in their growth, there is no need for peeling or slicing, just a good rinse before cooking.

Bradford Angier’s “Field Guide to Edible Wild Plants” comments that the many species of knotweeds have long been relished and relied upon by animals and humans, especially Indigenous peoples in cold parts of the world; grouse and other large, wild birds snap up the seeds while deer browse on the plants.

Angier’s “Field Guide to Medicinal Wild Plants” adds that there are 30 to 50 species of knotweed, all in the buckwheat family, on this continent. Perhaps the most widely known and used is Japanese knotweed, with its “innumerable greenish-white blossoms later erupting in multibranched clusters between the stalks and leaves.” Leaves of Japanese knotweed come to an abrupt point – one of the ways to distinguish it from other knotweeds.

Japanese knotweed shoots are delicately delicious when no more than a foot tall and before the leaves start to unfurl. Cut the fat shoots with a sharp knife close to the ground, Angier says. Remove any open leaves and drop in boiling, salted water for about 5 minutes, until fork-tender, and serve hot with butter or cold with mayonnaise. After stalks grow beyond a foot, the stalks can be harvested and sliced crosswise like rhubarb.

Please note: This article is for informational purposes only. It is not intended to substitute for professional medical advice, diagnosis or treatment. Please consult your health care practitioner about serious medical issues.

Scroll to Top
Sign up to receive our weekly newsletter of happenings at MOFGA.