Rare Bohemian Knotweed could be on the march, warns Environet

20 October 2020: Bohemian knotweed, a rare hybrid of the highly invasive Japanese knotweed and its cousin Giant knotweed, is causing problems for homeowners as it’s not so easily recognised and can be just as invasive, warns Environet UK.

The plant was recently found growing in a garden in Aylesbury, Buckinghamshire by homeowner Stuart Marshall who inherited the property and is renovating it to sell. He discovered the plant whilst clearing the garden and unsure what it was, he attempted to dig it out but when it kept growing back, he became suspicious and contacted invasive plants specialists Environet UK. They identified it as the unusual variety of knotweed which can be just as invasive and vigorous as both its parents.

Reports of Bohemian knotweed (Fallopia Bohemica), which is produced by cross fertilisation between Japanese knotweed and Giant knotweed, are on the rise, according to the Property Care Association. Unlike its parent plants, it has the potential to produce male plants and set seed, enabling it to spread more rapidly – and the fact that it’s not so easily recognised means it is often left to grow unchallenged.

As well as outcompeting native species, its vast root system has the potential to cause damage to property, including patios and driveways, which is seldom covered by buildings insurance, meaning the plant should be treated or removed as quickly as possible. When selling a property, sellers are asked a direct question about Japanese knotweed and whether the property is or has been affected. From the legal perspective, the advice is to declare the presence of Bohemian knotweed if they’re aware it is, or has been, growing on their property to avoid the risk of future legal action against them, even though strictly speaking it is not Japanese knotweed.

Stuart Marshall said:

“I was clearing the garden when I came across the plant which seemed to be growing vigorously, but otherwise didn’t look particularly menacing. I only became suspicious that it might be invasive when my attempts to remove it failed. Environet immediately identified it as Bohemian knotweed which I’d never heard of before. I’m renovating the house to sell so decided to have the plant excavated, which only takes a couple of days, with a root barrier installed to protect the home in the future.”

Stuart Marshall surrounded by Bohemian knotweed in his garden in Buckinghamshire
(Credit: Environet UK).

Nic Seal, Founder and Managing Director of Environet UK, added:

“Stuart’s decision to act quickly and decisively means the infestation can be removed and his sale should proceed unhindered. While Japanese knotweed is by far the most prevalent variety, all types of knotweed are potentially problematic and should be dealt with quickly to avoid risk of damage to property, legal cases relating to encroachment or problems selling in the future. Evidence of a professional treatment plan and an insurance-backed guarantee for the work should be enough to satisfy any mortgage lender, although sellers may find there’s still some diminution in the value of the property due to the associated knotweed stigma.”

How to identify Bohemian Knotweed:

• It has green leaves which are either heart shaped or square ended. Both types can appear on the same plant.
• Leaves are larger than Japanese knotweed, but smaller than Giant knotweed, and have short hairs on the underside.
• Plants usually grow 2 – 3 metres high.
• It blooms in late summer, with small green-white or cream-white flowers that grow in plumed clusters.
• Cane-like stems are reddish-brown in colour. The plant dies back above ground in the autumn, but the canes usually remain standing.

Kindly shared by Environet UK