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Japanese Knotweed: what you need to know

Posted on 2015-07-21

A headache for landlords and tenants alike, Japanese Knotweed was brought to the country because of its beauty. Now, however, it’s a thorn in the side of property occupiers and owners.

Japanese Knotweed is problematic because of the rate it grows at and how seemingly challenging it is to get rid of. As a direct result of these factors, it can be impossible to let a home with Japanese Knotweed on the premises, and some banks refuse to approve mortgages, with the presence of the weed knocking tens of thousands of pounds from property prices.

How to find out if you have Knotweed on your land

Japanese Knotweed begins growing in spring months. By May, it can be as big as 1.5m, and 3m by June. Over the autumn, it dies down, and appears to have almost entirely disappeared over the winter months. But, in the height of summer, where it can grow by as much as 20-30cm per day, what signs should you look out for that show you may have a Japanese Knotweed problem?

  • Red shoots breaking through the ground 
  • Heart or spade shaped leaves
  • A hollow stem 
  • Clusters of white flowers that are attracting bees

What’s the problem?

As well as potentially making your property unlettable, and knocking tens of thousands of pounds off its value, Japanese Knotweed can cause several problems. 

In its native Japan, the climate and regular ash deposits prevent the weed from growing, although its deep root system allows it to survive. However, in England, there are no ash deposits, and, because the climate is different, it can grow without hindrance. Its strength means that it can even grow through tarmac and brickwork, leading to significant structural problems for houses.

How can I get rid of it?

If you find Japanese Knotweed on your property, or the property you’re letting, then there’s no need to panic, as there are several ways that you can get rid of it.

1) Dig it out

If you spot Japanese Knotweed on your property while it’s still in its infancy, you can dig it out. However, you have to be careful. It only requires just over 0.5cm of root to regrow, so you have to make sure it’s all fully removed.

Due to how quickly and easily it spreads, Japanese Knotweed is also classified as ‘controlled waste’, which means that you can only dispose of it on a licensed landfill site.

2) Kill it with chemicals

Japanese Knotweed can be killed with chemicals, but it can take up to five years to completely kill the weed. Professional treatments can cost thousands of pounds. Treatments containing glyphosate help, but be prepared to be in it for the long haul.

3) Cook up a storm

Finally, Japanese Knotweed can be eaten. However, if your garden is infested, it’ll take a substantial amount of knotweed compote to solve the problem.

If you do discover Japanese Knotweed, then it’s best to inform the experts and see how you can clear it safely and responsibly. Remember, it grows incredibly quickly, so act immediately. To find out more - or talk to someone in the know – contact The Environment Agency on 0370 850 6506.

Image courtesy of Shutterstock

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