Japanese knotweed is a pioneer species that is believed to have its origins in the volcanic mountains of Japan some 150 million years ago. Its ability to survive in hostile conditions at high altitude, helped it to gradually spread across what is recognised as its native territory of Japan, Korea, Taiwan and parts of China.

Across Japan it is known as Itadori, and is foraged for food and used in traditional medicines. Japanese knotweed is known to contain resveratrol, a chemical also found in red grapes, which is thought to act like antioxidants do, protecting the body against damage that can put you at higher risk of things like cancer and heart disease.

Crossing continents

During the Victorian era, European pioneers travelled the world collecting exotic plant and animal specimens to bring home and sell – In effect founding the horticultural market as we now know it. It was one such pioneer, a Bavarian physician and keen botanist Philipp Franz Von Siebold who came across Japanese knotweed. Siebold collected thousands of plants during his posting in Japan in the Dutch trading post on Deshima, including many of our garden favourites such as the peony-rose, hydrangea, camellia and wisteria. 

Siebold returned to Holland with his collection and founded a commercial nursery in 1840. From there, samples of his plants were distributed and sold across Europe. Japanese knotweed was sent to Kew Gardens in London in 1850, and with a gold medal awarded by the Agricultural and Horticultural Society in Utrecht to its name, it became a firm favourite amongst nurserymen and gardeners alike.

There are also reports that an earlier sample was sent to the Royal Horticultural Society in London in 1825 – although it is not believed to have been widely distributed at that time. 

Japanese knotweed has now spread across the continents and is a problem in several countries including North America, Canada and New Zealand.

A look at the UK

By 1869 Japanese knotweed was widely available for sale to the public in the UK and was even used by farmers as animal feed. It was also noted for its industrial applications such as the stabilisation of railway embankments and spoil from mines.

As we know, fashions come and fashions go, and by the time the fashion went there was no stopping the invasive species spreading throughout the UK. The rapid industrialisation and development of infrastructure across the country, coupled with the lack of biosecurity allowed knotweed to spread exponentially. 

By 1900 it had been reported as naturalised across the UK, where it was found growing outside of gardens in many parts of the country. As early as the 1930s, it started to negatively affect the price of housing, and was known locally in Cornwall as “Hancock’s curse”. 

We now estimate that up to 1 in 20 residential properties are affected in some way by Japanese knotweed, with a presence in every 10 square km patch of the UK.