Japanese knotweed

The dangers of Japanese knotweed



If you’re a homeowner looking for information about the dangers of Japanese knotweed, or a construction site manager looking to brush up your knowledge, Build-Zone has put together a guide that tells you everything you need to know.

Why does it matter?

The plant – which originates in Japan – has become more out of control in the UK as we don’t have any natural predators to stop it spreading. This affects the construction industry massively because of its ability to damage concrete, buildings, tarmac and more. It has been known to block footpaths and constructions, such as flood defences. 

Because of its invasive nature, it is infamous for impeding the sale of buildings. The long-term effects can make many properties unsellable because the weed decreases its value. This can cause huge problems for builders, developers and homeowners alike. 

What are the dangers?

There is a multitude of reasons why Japanese knotweed is dangerous, from the way it grows to how you get rid of it. Here are a few of the main ones:

It’s rapid growing: Japanese knotweed is the UK’s fastest-growing invasive weed. During its peak time in the summer months, it can spread by as much as 10cm a day. What may look like a small weed can suddenly become a huge problem if left to its own devices.

It has large root systems: The reason why this plant can do so much damage is because it has such a wide-ranging root system. Growing metres in all directions, this plant can destroy the foundations of buildings and drains if left to grow and spread.

It’s difficult to get rid of: Getting rid of this pesky plant is more difficult than you might think. It’s not simply a case of picking it out, because if care is not taken, trying to chop it down can cause it to re-grow fast. Proper treatment of the plant can take months and often needs to be surveyed and treated by professionals.

It’s hard to identify: Japanese knotweed has a few very distinctive features, but it can look similar to other plants. The plant has fairly large, heart-shaped green leaves that are around 10cm long. They also have bamboo-like stems and can grow flowers in late summer. However, like most other plants, they go brown and the leaves fall off. 

It affects lenders: Most lenders will not offer financial loans for developments or properties that have Japanese knotweed or even a history of the plant. But, Build-Zone – as an extension of Sennocke – has negotiated a Lloyd’s insurance-backed guarantee facility for Japanese knotweed. This brings a solution to developers and consumers for this major problem. Build-Zone is working with Japanese knotweed removal companies, which can guarantee removal for up to 10 years.


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