How Did Japanese knotweed Get Here?

By Paolo Martini on 25th February 2020 (updated: 26th February 2020) in News

Japanese knotweed is a contentious plant that can depreciate the value of a property and cause conflict between neighbours. The invasive plant is known for spreading quickly and for monopolising gardens. Knotweed grows in large patches that can quickly push out any other competing plant life. Thankfully, Japanese knotweed is easy to identify, so homeowners can waste no time in getting a treatment plan in place to get rid of the plant.

Although there is plenty of discussion regarding how Japanese knotweed spreads, and what to do if you’ve bought a property with knotweed, how this plant first got to the UK is not usually discussed. Japanese knotweed’s history is an interesting one and can help give insight into why it has flourished so well in the UK and what lessons can be learned when dealing with invasive plants in the future.

Where is Japanese knotweed originally from?

Japanese knotweed is originally from Japan and is also native to China and Korea. The plant is one of many species of plants that have been discovered to be growing on the side of volcanoes. In its native land, Japanese knotweed can reproduce naturally and also benefits from a prodigious underground system of rhizomes. In its native environment, knotweed is kept in check by natural predators in the form of fungi and insects, not to mention other plants and an environment that can be much more hostile than the United Kingdom.

The plant was originally discovered by Dutch naturalist Maarten Houttuyn in the 18th-Century, he named it Reynoutria japonica, a name which it still goes by today. Unfortunately, the records of this original discovery were lost for some time, so when more European botanists started exploring Japan some 150 years later, the plant was rediscovered and given a new name by a Bavarian botanist, Phillip von Siebold. Siebold and his partner Zuccarini, named the plant Polygonum cuspidatum. It wasn’t until the turn of the 20th century that a Japanese botanist by the name of Makino, discovered that Houttuyn and Siebold’s plant were one and the same.

Who brought Japanese knotweed to the UK?

Philip von Siebold brought Japanese knotweed to the UK in 1850, unaware of the impact that it would go on to have on the environment. At the time, botany and the cultivation of plants was a popular interest of the upper classes. Botanist like Siebold would be able to fund their research trips by sending their discoveries back to nurseries on the European continent, where they would then be cultivated and sold onto commercial nurseries or botanical gardens around the world.

Why was Japanese knotweed imported to the UK?

Japanese knotweed was imported to the UK for commercial sale and botanical cultivation. Over the time that he spent in Japan, Siebold collected and recorded over 1,000 different plants, often choosing to plant them in the garden behind his research base on Dejima, an artificial island near Nagasaki. Periodically, Siebold would box up a number of samples and send them back to his home in the Netherland. From their new home in Leiden, these plants would be carefully grown and the packaged up for botanical gardens in Belgium and Britain, with an unmarked box containing Japanese knotweed arriving at London’s Kew Gardens in 1850.

Kew Gardens often relied on these boxes of new plants to keep their own collections diverse and interesting for visitors. After discovering how quickly the plant could grow in Britain, the horticulturists there recognised Japanese knotweed as a plant that could be easily cultivated and sold on to budding gardeners. Soon the plant was being distributed to garden nurseries around the country and then shared in cuttings by enthusiastic gardeners. In addition to being intentionally spread by people, the plant also began to spread by its own means, populating river banks and finding new routes to the rest of the country along roads and newly built railway lines.

Where does Japanese knotweed grow in UK?

Japanese knotweed now grows in almost every area of the UK. The plant was given free rein to spread throughout the country for over a hundred years before being recognised as invasive by the government. By the time Japanese knotweed was identified as an invasive threat in 1981, it had already been spread by gardeners, dug up and transported by urban development projects and even used to stabilise soil on the sides of railway lines.

The plant is frequently found growing alongside public watercourses such as canals, as well as near railway lines, motorways and public footpaths. Japanese knotweed thrives in most conditions in the UK and is often found growing on land that has been abandoned or left unattended. For this reason, large infestations can often be discovered in overgrown back gardens, or on abandoned industrial sites.

How common is Japanese knotweed in the UK?

Japanese knotweed is a very common sight in the UK. Since the government has made the spread of Japanese knotweed a more pressing concern, efforts have been made to track where it has been growing throughout the country. Using these statistics, it’s been possible to recognise the areas of the country that have been most affected by Japanese knotweed. Bolton, Bristol, Conwy, Rotherham and Nottingham are areas in the UK that have been affected the most, however exact numbers are difficult to assess

Related: Japanese Knotweed UK Map

What do I do if I find Japanese knotweed?

If you find Japanese knotweed it’s important to ascertain where the plant has come from and to what extent the plant affects your property. You may want to consider contacting a Japanese knotweed specialist to make a positive identification before you move forward with talking to any neighbours who might also have the plant on their land. Ignoring the infestation is not advised, as the plant can quickly multiply, leading to a larger problem to deal with and potentially more costs, if you find that it’s not possible to claim compensation for the cost of treatment.

If you think you’ve found Japanese knotweed and would like some advice on what to do next, then you can contact us by calling 0151 668 0551 or send us a message using the contact form on this page. 

Paolo Martini

Paolo Martini is the lead solicitor for Knotweed Help and has over 30 years of experience in the field of Civil Litigation and is an expert on the legal issues faced by individuals dealing with Japanese knotweed on their land. Now considered one of the country's leading litigators in Japanese knotweed law he works alongside the country’s top barristers and experts. His in-depth legal experience and connections to the Japanese knotweed removal industry make him uniquely suited for handling your case.