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A Listener Wrote To Ask About One Of The Worst Invasive Weeds There Is
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

May 10, 2015

This old steam engine only a few years ago sat all by itself. Now, after the first growth of Japanese knotweed it is almost covered in the invasive weed. Below, the leaves and distinctive stems of Japanese knotweed; and the creamy-white flowers that appear in late summer and fall. Photos by Jaap Tamminga, Ontario Ministry of Natural Resources; and Ontario Federation of Anglers and Hunters respectively.



Thelma Rickler living in British Columbia wrote recently inquiring about a weed that has plagued me for well over half a century. The most common name is Japanese knotweed (Fallopia japonica) and I first encountered it as a kid back in the mid-fifties while looking after my mother’s vegetable garden on Hopedale Avenue in East York (Toronto). Both the back section of a relatively small backyard and that of the next-door neighbour had this stuff that grew at a tremendously great rate and could easily attain a height of three metres each growing season.

Basically it was an herbaceous perennial and disappeared each fall, only to appear as robust as ever the following spring.

Just pulling it out was useless because it just re-grew from wherever the stems were broken off. We had a very sandy soil in that Hopedale garden, almost as sandy as what we have here on the beach adjacent to the Salish Sea (Strait of Georgia), which seemed to allow the roots to grow at least as rampantly as the stems and foliage.

All of that was before I attended The Niagara Parks Commission School of Horticulture and so my knowledge of using appropriate herbicides was little or none.

After my graduation in 1961 I eventually worked for Sheridan Nurseries and at our head office we had three raised and contained beds in which topiary trees and a medium-height groundcover known as Russian vine (Fallopia aubertii or Polygonum aubertii) a close relative of Japanese knotweed grew. Since the raised growing beds were lined with concrete that was covered with tar, it did not spread out of them easily.

For anyone encountering the invasive Japanese knotweed, we recommended applying RoundUp at about the time the plants came into flowering in mid-summer, and that worked for pretty well everyone who asked.

Now, however, with the backwards pesticide laws in Ontario, RoundUp is not available to average gardeners unless they make a trip to New York State and bring it back with them. [Not technically illegal since it is only a provincial law and the border people enforce only federal laws.]

Japanese knotweed in the family Polygonaceae, is native to Eastern Asia in Japan, China and Korea. In North America and Europe the species is very successful and has been classified as invasive in several countries. Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not closely related. While stems may reach a maximum height of 3–4 m each growing season, it is typical to see much smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down. The leaves are broad oval with a truncated base, 7–14 cm long and 5–12 cm broad. The flowers are small, cream or white, produced in erect clusters 6–15 cm long in late summer and early autumn.

Other English names for Japanese knotweed include fleeceflower, Himalayan fleece vine, monkeyweed, monkey fungus, Hancock's curse, elephant ears, pea shooters, donkey rhubarb (although it is not a rhubarb), sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo (though it is not a bamboo). In Chinese medicine, it is known as Huzhang which translates to "tiger stick."

Japanese Knotweed is often mistaken for bamboo; however it is easily distinguished by its broad leaves and its ability to survive Ontario winters. Japanese Knotweed is especially persistent due to its vigorous root system, which can spread nearly 10 metres from the parent stem and grow through concrete and asphalt. This invader is very persistent and once it becomes established, is incredibly difficult to control.

Japanese knotweed flowers are valued by some beekeepers as an important source of nectar for honeybees, at a time of year when little else is flowering. Japanese knotweed yields a monofloral honey, usually called bamboo honey by northeastern U.S. beekeepers, like a mild-flavored version of buckwheat honey (a related plant also in the Polygonaceae).

The young stems are edible as a spring vegetable, with a flavor similar to extremely sour rhubarb. In some locations, semi-cultivating Japanese knotweed for food has been used as a means of controlling knotweed populations that invade sensitive wetland areas and drive out the native vegetation. It is eaten in Japan as sansai or wild foraged vegetable.

Similarly to rhubarb, knotweed contains oxalic acid, which when eaten may aggravate conditions such as rheumatism, arthritis, gout, kidney stones or hyperacidity.

Both Japanese knotweed and giant knotweed are important concentrated sources of resveratrol and its glucoside piceid, replacing grape byproducts. Many large supplement sources of resveratrol now use Japanese knotweed and use its scientific name in the supplement labels. The plant is useful because of its year-round growth and robustness in different climates.


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