Who introduced Japanese knotweed to Britain?

Philipp Franz Balthasar von Siebold introduced Japanese knotweed to Britain in 1850. Then, with a little help from the upper crust of Victorian society, the plant spread far and wide. Today, Japanese knotweed is every homeowner’s worst nightmare.

So, is Philipp von Siebold really to blame for Britain’s Japanese knotweed crisis?

Japanese knotweed roots

Japanese knotweed (Fallopia japonica) is a much-adored plant in its native volcanic habitats of Japan, China and Korea. So much so that the Japanese word for it ‘itadori’, roughly translates to ‘take away pain’ and has been used to treat skin illnesses, fungal infections and even heart disease!

In Britain today, Japanese knotweed is far from adored, causing devastation to buildings and costing homeowners thousands of pounds in removal and legal fees. Worse still, some of us have known Japanese knotweed to grow through the very floorboards of homes and buildings – talk about The Day of the Triffids!

In its homeland, Japanese knotweed is kept under control by its natural enemy, the flea, as well as fungi and volcanic ash. When Philipp von Siebold brought the plant over, he left its predator behind, leaving the UK with few methods to keep it at bay. Essentially, Britain is ecologically ill-equipped to deal with such an aggressive plant, which is why it seems impossible to manage.

How Japanese knotweed took over Britain

The aristocracy of Victorian society found themselves rather in love with Japanese knotweed, and Holland’s 'Society of Agriculture and Horticulture' named it, “the most interesting ornamental plant of the year.”  Back in the UK, and without due diligence, the Victorians introduced Japanese knotweed into their London gardens and nurseries. 

Spreading invasive plant species in the UK

Over in Wales, the coal-mining valleys used the plant to stabilise the soil, whilst across Britain knotweed was used to line the countries railway lines, and any clippings were thrown away in rivers and streams. (Even today, those living in London, the Welsh valleys, near railway lines and watercourses are far more likely to suffer from an infestation of Japanese knotweed.)

So it’s all-too-easy to see how this invasive plant took over Britain. In fact, the only area of Britain still unaffected by Japanese knotweed is the Orkney Isles!

Why is Japanese knotweed so strong? 

By 1870, Japanese knotweed had well and truly rooted itself in British soil.  Whilst it is true to say that Philipp von Siebold introduced the plant to the UK, and the Victorians helped it spread like wildfire, we would be wrong to assume Japanese knotweed didn’t have its own fighting spirit – its strength is the very reason why it is so difficult to remove it from our gardens today.

The reason this non-native species is so robust is due to the fact that its energy is stored in its complicated root system. Like an iceberg, the plant mostly lies below ground – up to 3 metres deep – and is thus protected from the elements. Remember, this root can spread underground up to seven metres vertically from the root. This is why it has become such a nuisance to remove, and is so strong.