How to Identify
Japanese Knotweed
Oh, the Horror!
There are two types of people when it comes to Japanese knotweed. There are those who might not have heard of it and live in ignorant bliss. Then there are those who wake up screaming because this plant haunts their nightmares. Japanese knotweed can be a scary plant, and here’s why.
A Knotty Neighbor
Knotweed's bamboo-like shoots begin growing quickly and aggressively (4-15 cm a day) in early spring before other plants have a chance to grow(1). Their roots release chemicals into the soil that inhibit the germination and growth of other plants, preventing competition(2). As a result, huge stands of Japanese knotweed can rapidly consume roadsides, forests, or pretty much anywhere(1). Even in your home...
Knot the rhizomes!
To make matters worse, these plants are capable of tolerating a wide range of conditions, from full sun to shade and moist to dry soil(1). But the ultimate kicker is that Japanese knotweed is extremely difficult to eradicate.
Its seeds can float along streams and glide through the wind(2). More tedious are the plant's rhizomes. It cannot simply be mowed down or pulled up. Japanese knotweed has long, deep-growing rhizomatous roots that allow it to clone itself and multiply(2). Even if the teensiest bit of rhizome is left alive underground or scattered to a new location, the plant can regenerate and resume its torment(1).
Successfully removing Japanese knotweed is a tedious, expensive, and sometimes dangerous task. The go-to solution is the application of herbicides to ensure the elimination of all living tissue, including the rhizomes(3).
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Photo by Tom Heutte, USDA Forest Service, Bugwood.org / via Wikimedia Commons.
The Rhizomes of Japanese Knotweed
Knotweed Apologist
But hang on a minute. Is Japanese knotweed pure evil? Sure, from this perspective, it seems like a big, bad plant. However, in its native habitat of Japan, China, Korea, and Taiwan(2), it does a whole lot of good. After a lava flow has oozed over a large area and cooled, Japanese knotweed is one of the first species to start growing, helping other species to populate on the lava rock(4). Depending on location, Japanese knotweed can either smother or encourage biodiversity.
Disastrous Garden Trends
In the late 1880s, plants from Asia would become a popular part of garden and landscaping fashion in Europe and the United States(5). Ironically, most invasive species in North America have been introduced by these gardens and nurseries(5).
The Goodwin Garden is based on an original 1862 landscape plan. The garden features bedding annuals and plants from around the world. Located in Portsmouth, New Hampshire.
“U.S. Japan Fleet, Com. Perry Carrying the ‘Gospel of God’ to the Heathen, 1853.”
Painting by James G. Evans, 1853
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A Japanese woodblock print of Perry (center) and other high-ranking American seamen
Unknown artist, 1854
Poetic Justice
The catalyst for this introduction of even more non-native plants around this period in time is largely due to forcibly opening Japan’s borders(1).
In 1640, Japan had initiated sakoku or a “closed country” policy(6). This meant self-isolation from most foreign powers, especially European nations that relentlessly tried to religiously convert Japan and engaged in unfair trading practices(7).
However, in 1853, Commodore Matthew Perry led an imposing US fleet of warships to Japan, resulting in the forced opening to the West(6). While the diplomatic interaction remained peaceful, the visits were anything but friendly(6). For Perry and his crew, their mission was not only to be able to trade with the country but to “elevate” the people to a higher state of civilization by introducing western culture(6). Religious idols and temples were affronted(6). Overly dramatic parades and ceremonies were orchestrated to impress the people with the greatness of the United States(6).
In 1854, after Perry arrived a second time with an even larger fleet of threatening ships, Japan begrudgingly agreed to re-establish trade with the US(8). For the remainder of the 1800s, ornamental plants from Japan were popular in Europe and the US, including the incredibly invasive Japanese Knotweed(5).
Perhaps Japanese Knotweed can serve as a reminder of the consequences for imposing superiority over others.
Harvesting Japanese Knotweed
Does harvesting actually help get rid of it?
Sadly, no. As long as the root system remains intact it can still spread. In order to stop knotweed from spreading, you have to completely remove the entire plant, above and belowground, which is extremely difficult. However, foraging Japanese Knotweed can be extremely educational.
If you are going to harvest, take everything. Don't leave any parts of the plant behind. Scattering parts of the plant may inadvertently spread the Knotweed.
Shoots
Harvest in the spring when the young shoots are about a foot tall. This is when they are tender and flavorful. Stems start to toughen as they grow. Simply pull them a couple inches from the base where it is thicker. It will make a satisfying "pop" noise.
Recipes
Japanese Knotweed can be enjoyed as a savory snack or a sweet treat!
However, it is extremely important to properly dispose of the scraps. The easiest way is to microwave leftover bits ensuring the tissue is dead before throwing them into the trash. Do not compost.
Raw: tangy, sour, crunchy
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eat the stalks raw like a celery stick
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pickle it
Cooked: lemony, rhubarb
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sautéed
References
1. Tredici, P. (2010). Wild Urban Plants of the Northeast: a Field Guide. Cornell University Press.
2. Kato-Noguchi, H. (2022). Allelopathy of knotweeds as invasive plants. Plants, 11(1), 3. doi:https://doi.org/10.3390/plants11010003
3. United States Department of Agriculture. (2007). Invasive Plant: Japanese Knotweed [Fact Sheet].
4. ADACHI, N., TERASHIMA, I., & TAKAHASHI, M. (1996). Central die-back of monoclonal stands of reynoutria japonicain an early stage of primary succession on mount fuji. Annals of Botany, 77(5), 477–486. https://doi.org/10.1006/anbo.1996.0058
5. Van Kleunen, M., Essl, F., Pergl, J., Brundu, G., Carboni, M., Dullinger, S., Early, R., González‐moreno, P., Groom, Q. J., Hulme, P. E., Kueffer, C., Kühn, I., Máguas, C., Maurel, N., Novoa, A., Parepa, M., Pyšek, P., Seebens, H., Tanner, R., . . . Dehnen‐schmutz, K. (2018). The changing role of ornamental horticulture in alien plant invasions. Wiley. https://doi.org/10.1111/brv.12402
6. KEITH, J. A. (2011). Civilization, Race, and the Japan Expedition’s Cultural Diplomacy, 1853–1854. Diplomatic History, 35(2), 179–202. http://www.jstor.org/stable/24916476
7. Munez, E. (n.d.). Sakoku. Encyclopædia Britannica. https://www.britannica.com/topic/sakoku
8. U.S. Department of State. (n.d.). The United States and the Opening to Japan, 1853. Office of the Historian. https://history.state.gov/milestones/1830-1860/opening-to-japan