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13 Aug 2020
Georgina Kent Georgina Kent

Everything you need to know about Japanese knotweed


Japanese Knotweed leaves and flowers

You’re sat at home in the garden admiring all the beautiful flora. In the distance you see a beautiful leafy plant with delicate flowers.

You remember reading about Japanese knotweed and realise this plant looks very similar. Here’s what you need to know.

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Do I have Japanese knotweed and what does it look like?

Japanese knotweed is pretty distinct looking. Reddish stems, large leaves, and pretty little cream flowers.

It grows at a very quick pace, up to 10cm a day in the Summer months. Its roots can grow through tough ground like tarmac, making it pretty aggressive.

Chances are, by the time you’ve spotted it, its roots are already over two metres from it growing out in all directions.


A close up of Japanese knotweed, himalayan balsam and giant hogweed leaves

How to tell the difference between Japanese knotweed, Himalayan balsam and giant hogweed

Each has pretty distinctive leaves, that’s the easiest way to tell them apart.

  • Japanese knotweed has spade shaped leaves, with a point at the end – so they’re quite broad leaves

  • Himalayan balsam has much narrower pointy leaves

  • Giant hogweed’s leaves are narrow with spikes all the way down, a little like nettles


How does it spread?

It spreads via what are known as the rhizomes, which are underground stems, and at speed. It will grow through most materials, other than concrete and brick.

If there are any cracks in foundations, it can grow through them. Also, if there's any weakness with underground pipes, it can compromise them too.

It’s a very hardy plant and thrives while growing in difficult circumstances. And with very little light.

Is it dangerous to handle?

Yes and no. It’s not poisonous. But if a small fragment of it remains on you and can deposit somewhere else, there’s a good chance it’ll grow there too.

That makes handling it dangerous as it could lead to more destruction.

What damage can Japanese knotweed do?

Pretty extensive damage. While it can’t grow through bricks and concrete, it can work its way through small cracks and gaps.

A Google image search shows pictures of it growing through floor boards and walls in people’s homes. Anywhere it can get through.

It can cause damage to foundations, patios, walls and more if left untreated. This is why mortgage lenders take it seriously.

What you mustn’t do is ignore it, especially if it’s within your property boundaries. Act straight away. 

Japanese knotweed can grow as much as 1ft a week during the summer months. But the real growth and damage is under the ground.

If it’s outside your property boundaries, call your local council to see if they’re able to eradicate it.

How can I get rid of it?

Doing it yourself 

While it’s possible to remove it yourself, we recommend asking professionals to do it. At least, if you want the best chance of it remaining gone, that is.

If you’re going to do it yourself, you’re going to need a lot of determination and patience. First off, here’s some kit you’ll need:

  • Some coveralls

  • A visor or face shield

  • Face mask to P3 standards

  • Disposable shoe/boot covers

  • Glyphosate weed killer

  • A knapsack style sprayer

  • Some rubber gloves

We’d also recommend researching the DIY removal process as you have to be very diligent in how you go about things. We found to list the process clearly and step-by-step.

Here are a few tips to keep in mind if you’re thinking of removing it yourself:

  • It can take 3-5 years to completely remove it

  • Do not put any part of the knotweed plant, dead or alive, in your compost

  • It must be disposed of in a licensed waste disposal centre (including the soil dug up with the knotweed).
    It’s best to call the centre to ensure they’re able to accept it. It’s worth calling your local council to ensure you’re allowed to transport it to the waste disposal centre too.

If you are going to dispose of it yourself, be sure to call the Environment Agency first. For example, if you're planning on burning it, they'll need a week's notice first.

Paying someone else to do it 

This is the most recommended method for effective removal of Japanese knotweed. But be prepared, as it’s not cheap.

We’ve looked at quotes from a range of specialists online. Prices went from as low as £1,000 up to £20,000 depending on the provider.

The level of removal and guarantee you select dramatically affect the price.

Opting to have it chemically injected is one of the cheaper options. Whereas having the area excavated to remove all rhizomes is pricier.

The specialist you appoint will recommend what the best removal option is for you. And go through your options.

We’d urge you to get at least three quotes and discuss what the options for removal are, and the costs.

READ MORE: Hiring a tradesperson

Will it affect my mortgage?

If you already have a mortgage and have noticed Japanese knotweed start to grow, your mortgage is already in place, so don’t worry.

If you’re seeking a new mortgage, your options are likely to be more limited. Some providers will decline, but some will want a survey done.

The surveyor will most likely be by a Property Care Association (PCA)-approved surveyor. They’ll likely want the removal specialist to be PCA-approved too.

They’ll want to know how close it is in metres to the property, specifically if it’s more or less than 7m away. If it’s very close, they’ll likely want it removed by an approved specialist.

This is all before the mortgage is given. It’s not all bad news. In 2018 some new research came out about how serious Japanese knotweed is.

As a result of this research, many mortgage providers are now more lenient.

Will Japanese knotweed affect my home insurance?

It most likely won’t have any impact on your home insurance. That's because most home insurance providers won’t offer any cover for it.

You will be responsible for paying for it to be removed. And for any damage it causes to both your property and neighbouring properties.

Should things to come it, if you have legal cover as part of your home insurance, you might be able to use that to get legal advice.

READ MORE: Home insurance legal cover


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