What is the Cost of Removing Japanese Knotweed in 2021? | Checkatrade
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Cost of removing Japanese knotweed
by
Checkatrade

How much does it cost to remove Japanese knotweed?

Japanese knotweed is a weed that can grow to over two metres high and spread rapidly. If you have it growing in your garden, you’ll want to get it removed as soon as you can. But what’s the cost of removing Japanese knotweed? We’ll reveal all below.

Type of removal serviceUnit of cost Cost + VAT
(Range low - high)
Average cost
Average cost of domestic knotweed removalPer project£1,500 - £2,000£1,750
Typical removal methods
Domestic herbicide treatment (<49 m2)Per project£950 - £2,950 £1,750
Full excavation & removal (<49 m2)Per project£4,000 - £20,000£6,500
Alternative methods
Sifting and screening (<49 m2)Per project£1,750 - £4,950£3,350
Excavation & root barriers (<49 m2)Per project£1,750 - £4,950£3,350
Excavation, on-site relocation & ongoing herbicide treatment (<49 m2)Per project£4,000 - £20,000£6,500
On-site burial (<49 m2)Per project£4,000 - £14,950£9,475

Remove Japanese knotweed cost

First things first, it’s important to note that if you don’t deal with a Japanese knotweed infestation professionally and thoroughly, you could seriously impact your house’s value. In fact, you may even need guarantees of professionally completed works when you come to sell your home.

Not only that but failing to deal with an infestation could lead to legal claims from affected neighbours. This could add up to tens or even hundreds of times the cost of removing Japanese knotweed in the first place.

The cheapest way to deal with a Japanese knotweed infestation is with herbicide treatment. However, this is generally recognised as being a ‘control’ rather than a one-off solution, because there’s a risk of dormancy and regrowth, especially on land that’s disturbed.

At the other end of the scale, you can get Japanese knotweed excavated and disposed of at landfill, known as dig and dump. This will cost around ten times the amount of herbicide treatment, but it’s a more permanent solution.

How to identify Japanese knotweed

Japanese knotweed can usually be recognised by its heart or spade-shaped leaves, which are smooth and mid-green in colour. That said, it can be easy to mistake other plants for Japanese knotweed, such as bindweed, houttuynia and even bamboo.

If you think you may have Japanese knotweed growing in your garden, you’ll want to get a survey conducted by a professional.

Factors that influence the cost of removing Japanese knotweed

A PCA qualified surveyor will take a number of factors into account to determine the cost of removing Japanese knotweed and the best method.

Arguably, the most important factor is the size of the area affected and the extent of growth. The weed’s roots can grow up to three metres deep into the ground, making it extremely difficult to completely remove. Plus, if even the smallest part of the plant is left in the soil, it could quickly return.

Other elements a surveyor would review include:

  • The location.
  • Nearby watercourses.
  • Access issues.
  • Whether the property backs onto Network Rail land.
  • Its distance from habitable space.
  • Whether it’s encroaching from or onto neighbouring property.

After the survey, a professional will usually offer a management plan to outline the best methods of controlling or treating the infestation. Some professionals will include a 10-year warranty and an insurance-backed guarantee for their services.

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What is the process to remove Japanese knotweed?Cost to remove Japanese knotweed

There are a number of different processes that can be used, and these will all affect the cost of removing Japanese knotweed.

However, there are only two that are commonly used, especially in domestic settings. These are:

Herbicide treatment

Herbicide treatment is a long-term solution for managing and controlling Japanese knotweed as opposed to completely eradicating it. You’re looking at a starting cost of around £950 to deal just a couple of square feet.

There are a number of pesticides that are effective on Japanese knotweed, but we’d recommend working with a professional who’ll be likely to have access to stronger herbicides. Herbicides are usually sprayed onto the leaves of the plant (although if you’re keen not to damage neighbouring plants, there’s also the option to use herbicide stem injections).

You’ll usually need to repeat the treatment two to three times a year. Often, after three to five years, the knotweed will stop growing back, at which point you may be able to cease treatment. Make sure that you work with a qualified PCA Surveyor who can give you a five-year plan and an insurance-backed guarantee to ensure you’re dealing with the problem effectively.

Excavation and removal

Known as a dig-out or dig and dump, excavating Japanese knotweed is a way to instantly eradicate the plant, as opposed to simply controlling it as is the case in herbicide treatment.

In this case, a professional will dig down to a depth of around two metres, and then transfer the waste to landfill. The waste is removed from the site as ‘controlled waste’ and disposed of in landfill sites that are fully licenced to receive Japanese knotweed.

This is a very effective method of Japanese knotweed removal, but it is more expensive than herbicide treatment. Prices tend to start at around £4,000 but will vary depending on the extent of the problem.

Japanese knotweed removal tips from an expert

We spoke to PCA specialist Simon Turner from Japanese Knotweed Group Ltd to get his top tips on dealing with Japanese knotweed. He advises:

“If you spot Japanese knotweed on your property, don’t dig it up. Leave it where it is and call in a PCA specialist. To sell your property, you’ll need a five-year plan and an insurance-backed guarantee, so make sure you’re getting a specialist in instead of paying someone thousands of pounds who might not actually solve the problem.”

Simon also advises that people looking to sell their property will often simply hide the problem by digging down a couple of feet into the ground to remove visible signs of a Japanese knotweed infestation. The knotweed will quickly grow back as you’ll need to dig down at least a couple of metres to have any effect.

If you’re selling your property, never hide the problem in this way – specialist knotweed solicitors are able to make claims against previous owners for failing to disclose a Japanese knotweed infestation to potential buyers.

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Other methods of removing Japanese knotweed

There are a number of other methods that can be used to remove Japanese knotweed, although they are pretty rare and wouldn’t usually be an option if you’re looking to remove Japanese knotweed from your garden. These are:

Sifting and screening

Sifting and screening is when the knotweed-infested soil is dug out and screened (both mechanically and manually) to remove any traces of the weed. The waste is then taken to landfill, while the non-infested soil can be used elsewhere on a development.

Soil screening can be a sustainable and cost-effective solution for removing Japanese knotweed, but it’s not a one-off treatment. It’s always possible that a small trace of knotweed slips through the net, so it should be used in conjunction with other removal methods.

Excavation and root barriers

In this method of Japanese knotweed removal, professionals are able to reduce the levels of contamination through excavation, before using root barriers to prevent the knotweed infestation from spreading (for example into neighbouring gardens). This reduces the amount of waste that has to be carried off-site to landfill.

Excavation and on-site relocation with ongoing herbicide treatment

Where there’s a lot of space, Japanese knotweed can be excavated and then removed to a lower risk location on-site, where it’s kept under control using herbicide treatment long-term. This is a more sustainable solution than dumping the waste in landfill and can also be more cost-effective (especially as Land Remediation Tax Relief can be claimed).

This method isn’t very often used in domestic settings as it’s better suited to larger sites, such as phased developments.

On-site burial

In this solution, after excavating the knotweed, it’s buried on-site in a deep burial pit, encapsulated in a cell. The top of the cell has to be at least two metres below ground levels so that it can’t be accidentally disturbed by humans or burrowing animals in future.

This solution can be a lot more cost-effective than disposing of the waste in landfill. However, it does require enough space for a large pit and so it often works best in areas that have been proposed for public open space.

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FAQssoil in this area contain Japanese Knotweed being treated

How long will it take to remove Japanese knotweed?

This will depend on the size of the area that’s affected and the severity of the problem.

How long does the Japanese knotweed herbicide take to work?

If the herbicide is applied to the leaves of the plant, it’s usually rainfast within 10 minutes. However, it requires repeat treatment over three to five years. If the plant is well established, it could take even longer.

What should you do with Japanese knotweed once you have cut it down?

Any Japanese knotweed that has been cut loose should be placed inside study plastic rubble sacks. These sacks need to be disposed of at a specialist landfill site.

Some councils in the UK offer free specialist collection services for Japanese knotweed. We’d recommend getting in touch with your local council to see if this is something they offer in your area.

How do I get rid of Japanese knotweed myself?

If you only have a small amount of Japanese knotweed present, you could try carrying out herbicide treatment yourself. Glyphosate-based products are best for controlling Japanese knotweed, with a typical 5l bottle of glyphosate-based herbicide costing around £30-£50.

That said, if you don’t have prior experience, we’d recommend leaving it to the professionals. There are safety considerations and the job needs to be carried out to nip the infestation in the bud.

Is Japanese knotweed a notifiable plant?

Although Japanese knotweed is a garden pest, there’s no statutory requirement to control, eradicate or even report its presence.

That said, it’s illegal to plant or cause Japanese knotweed to grow in the wild. Doing so could see you landed with fines of up to £5,000 or even a prison sentence of up to two years. Not only that but letting Japanese knotweed spread to private lands, such as your neighbour’s garden could lead to legal claims against you.

Can Japanese knotweed infestation stop me getting a mortgage?

This will depend on your mortgage lender, but many lenders will reject a mortgage outright if a survey indicates that there’s Japanese knotweed on the property.

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