The History of Japanese Knotweed in the UK

Japanese knotweed (Fallopia Japonica) is a fast-growing, bamboo-like perennial plant native to Japan and East Asia. Known for its strength and persistence, it was originally introduced to the UK in the mid-19th century as an ornamental plant due to its lush foliage and ability to grow rapidly.

From Garden Favourite to Invasive Species

By the late 1800s and into the 20th century, the aggressive nature of Japanese knotweed became more widely understood. Its ability to spread quickly and dominate landscapes led to serious concerns, and it was discouraged from being cultivated unless carefully controlled—a task that proved extremely difficult.

A Pattern of Introduced Species

The story of Japanese knotweed fits into a broader history of the British introduction of non-native species around the world. As the British Empire expanded, so too did the movement of plants and animals:

• In New Zealand, there were no native grasses or mammals before European settlement. Animals such as sheep and cows were introduced to replicate British agricultural conditions.

• In Australia, more than 30 species of invasive animals and over 500 species of non-native plants have disrupted local ecosystems. Rabbits, goats, and the infamous cane toad—introduced to control pests on sugar cane—have all caused long-term environmental issues.

These cases illustrate how non-native species, however well-intentioned their introduction, often lead to unexpected consequences.

Why Knotweed Thrives in the UK

In Japan, knotweed is naturally kept in check by native insects, fungi, and ecological competition. However, the UK lacks these natural controls. As a result, Japanese knotweed spreads aggressively and is now classified as an invasive plant species.

It is regulated under the Wildlife and Countryside Act 1981, which makes it a criminal offence to plant or cause Japanese knotweed to grow in the wild.