Japanese Knotweed - Fallopia japonica

Of all the UK’s invasive species, Japanese Knotweed (fig. 1) may have the worst reputation of the lot -  for good reason. Once it takes root, this plant is incredibly difficult to remove. Finding it on your property is bad news – it is illegal to sell property without declaring the presence of Japanese Knotweed, and very expensive to deal with (CEL Solicitors, 2020). 

Native Range and Distribution: 
Japanese Knotweed is native to various East Asian countries, including Japan, China and Taiwan (Shaw, 2013). The species entered Europe via the Netherlands in 1849 and was established in the UK by 1886 (NNSS, 2016). It is believed to have been sent to the UK from the Netherlands in 1850, as an ornamental plant for Kew Gardens. It then became popular as a garden ornamental and screening plant, contributing further to its spread (Shaw, 2013). 
As of today, Japanese Knotweed is widespread around the UK (fig. 2), with only small gaps in the Scottish Highlands (NBN Atlas, 2024). In the East Grampian region (fig. 3), the species is sparsely distributed around the northern section and along the Moray coast. In the city of Aberdeen, the species is much more common – this is likely the result of escape from gardens after intentional planting, as is common for the species. 

Habitat and Physical Characteristics: 
Japanese Knotweed is most concentrated around urban environments, often found in wastelands, riverbanks, and in gardens (NNSS, 2016). In the UK, it reproduces only through asexual means, meaning it does not produce seeds. Instead, new plants can grow from root fragments of the parent plant (Shaw, 2013) – they have even been known to take root in bins where they have been disposed of (CEL Solicitors, 2020). As such, their spread often comes about due to unintentional human distribution, or transport through rivers (Shaw, 2013). 
Known as rhizomes, the roots of the plant can reach 3 metres deep into the soil, and 7 metres wide (SISI, n.d.), while the stems can reach 2 metres high (NNSS, 2016). They can be identified by their shield shaped leaves, zig-zag stems, bamboo like appearance and purple speckles on their bark (Booy, Wade and White, n.d.). 

Impact: 
The ability of Japanese Knotweed to grow asexually from root pieces is what makes it so difficult to control. Any method of control that only removes the surface portion of the plant will fail, as the rhizomes will remain underground. This method may even cause the plant to grow back stronger (SISI, n.d.). The only effective method is to inject the plant with herbicide over multiple years, a process which takes up to half a decade to be fully effective (SISI, n.d.). 
The extent of time and labour required to remove Japanese Knotweed explains why treatment comes with such a financial burden. It is thought that an effort to totally rid the UK of the plant would cost as much as £1.56 billion (Shaw, 2013). The combination of annual treatments and the safe disposal of stems and contaminated soil makes the process a significant effort. 
Despite the costs, removal of the plant is essential. When found in urban environments, the stems have the potential to damage public infrastructure and the foundations of houses. In natural environments, the dense groups in which they grow can affect the growth of native species (SISI, n.d.). Along riverbanks they can contribute to an increased flooding risk by promoting riverbank erosion (Booy, Wade and White, n.d.), in addition to affecting fish populations if the river habitat is significantly altered (SISI, n.d.).