Japanese Knotweed
JAPANESE KNOTWEED
In Japan, the plant most of the world refers to as knotweed is commonly called itadori. This term means “take away pain,” as it was a source of various medicines, particularly laxatives, in traditional Japanese medicine. Knotweed grows here constantly and is not seen as a hazard, which is how much of the Western world views it.
I frequently see knotweed alongside the roads or cascading down the length of a bridge as I meander around the cities and countryside of this mystical country. But never have I heard here the dangers of knotweed or the need to eradicate it or to at least keep it under control. Here, knotweed growth is safe. It has its niche in the natural world and is kept at bay by its natural predators.
It’s a shame, really, that it has become such a problem in other places. In Japan it serves to add to the lushness of the hills and the romance of the mountains. Here, knotweed understands it cannot grow out of control. Here, the natural order of things demands its submission.
For help on how to identify Japanese knotweed, please visit our Japanese knotweed identification page.
HOW FAST DOES KNOTWEED GROW
Knotweed didn’t become a nuisance because it’s pretty or because it grows slowly. Just the opposite, in fact. Knotweed does grow fast. And it may be pretty, but it is deceptively so. Its ability to reproduce via its underground stems (called rhizomes) makes it incredibly capable of multiplying on a rather quick basis.
Knotweed can grow up to one meter per month and can reach heights of three meters. And not only will it grow in natural environments (countryside, forests, etc.) but it is infamous for stubbornly shooting through sidewalks, tarmac and water drains.
The rhizomes of a knotweed plant can stretch up to seven meters from the base of the plant and dive down to up to three meters. This helps it to grow even quicker since the merest hint of a rhizome that drifts from the main plant can create a whole new patch. Knotweed is hard to beat. And it is made difficult because of its ability to grow so quickly and so vastly in just a short amount of time.
JAPANESE KNOTWEED REMOVAL
There are various ways in which people have attempted to remove or at least control knotweed. The basic and most popular forms are through either the consistent use of herbicides or through physical removal.
When choosing to use an herbicide, it is essential to choose one with the right amount of concentration as well as use it when the plant is vulnerable (knotweed is more susceptible to herbicides during the months of March and October as these are their growing months.) It is believed that herbicides containing glyphosate is the most effective in eradicating knotweed.
Another option is to physically remove knotweed. But this option must focus on the destruction of the roots. If the roots are disposed with it is also critical to make sure that everything, including the stems, are disposed of as well, otherwise, it is likely that the knotweed will regrow. This is a process that must continue over time to ensure that the knotweed has been effectively eradicated.