It was Carl Peter Thunberg, the famous Swedish naturalist, who is recognized worldwide as the person who discovered Japanese knotweed, an event that happened toward the end of the 1700s. After this discovery, over 100 years later, a Bavarian naturalist for the Dutch Army named Philipp Franz Balthasar von Siebold, discovered knotweed again in the early 1800s. Von Siebold had a nursery, located in Leiden in Holland, and in 1848 began to distribute it throughout Europe. He marketed this plant heavily, riding on its success, after earning the prestigious Gold Medal given to him from the Society of Agriculture and Horticulture in Utrecht back in 1847. It sold well based on its highly publicized ability to grow and form dense screens. The sales of this plant were extensive and profitable which is why it began to proliferate throughout this area of the world.
How Did Knotweed Become A Problem In The UK?
An unpaid parcel of plants was later shipped to the Royal Botanical Gardens, located in Kew, in the mid-1850s, direct from the Leiden nursery in Amsterdam. A knotweed specimen was also sent to the Royal Botanic gardens around the same time, but this time it was sent to Edinburgh. A nursery in Kingston made knotweed for purchase in Britain. Commercial nurseries and amateur enthusiasts also began to promote it. Later it was naturalized in the UK, and all of this occurred before 1886. If you are in the UK you might want to take a look at ‘Knotweed Specialists UK‘.
End 19th Century Warnings About Knotweed
The people in the 1800s were well aware of the dangers of knotweed. In Alexandra Park, their flora in Oldham mentioned that knotweed had appeared on nearly all plots of cultivated ground. Gertrude Jekyll promoted Dwarf Japanese Knitting (Fallopia japonica) and stated that knotweed should not be planted, without some form of careful consideration, and that her Dwarf-knotweed needed to be cut back as much as possible. The Royal Horticultural Society told people do not to plant it unless it was carefully controlled.
After several years, eradicating knotweed virtually became an impossibility, and the situation became direr. Despite all of the warnings that had been provided by people and experts, it took until the early 1980s for the British government to finally create legislation designed to control the spread of knotweed (The Wildlife and Countryside Act).
In their assessment, knotweed was officially regarded as a threat and menace to the natural environment in which it was planted.
Since its introduction to the UK and Europe from Asia, the plant became a worldwide sensation and also a large problem. Outside of the parameters of its natural habitat, it was almost impossible to control. At least 30 species of insects and 6 species of fungus in Japan would naturally feed upon this plant which would prevent it from overspreading. It is because these species don’t exist outside of their natural habitat that the problem became untenable. The lack of natural predators in the UK and locations where it was growing was essentially making it unstoppable.
Trials in the UK were done to introduce natural predators of knotweed, predators that would come from Japan. The effects of this introduction have not been mimicked in these areas. Aphalara Itadori (a psyllid), were released in controlled areas, hoping to manage the knotweed. Scientists were able to say that after five years from their release, it is still too early to see any definable success.
They stated that it may take several more years to see any potential stoppage of this plant through natural predation. In the span of 5-10 years, the results could be promising. However, despite the promise of controlling Japanese knotweed, much remains to be seen.