If you’ve found Japanese knotweed in your home or you’ve discovered it’s present on a property you’re interested in buying, you’re probably wondering how much it costs to remove. 

Our guide tells you how much it will cost to remove Japanese knotweed, along with how to identify it, the impact of it on your property and what you can do to prevent it.

How much does Japanese knotweed removal cost?

The cost of removing Japanese knotweed in the UK can vary widely depending on the size of the infestation, the removal method used and the location of the property. On average, professional removal costs between £1,000 and £5,000 for smaller infestations and can exceed £10,000 for more severe cases. 

These costs are just estimates and may not include VAT. If your property requires excavation and disposal of contaminated soil, costs can rise to £20,000 or more. Ongoing treatment plans, such as herbicide application, may cost between £500 and £2,500 per year, depending on the size of the affected area.

Factors that affect the cost of Japanese knotweed removal

There are lots of factors that can affect the cost of Japanese knotweed removal. Your gardener may have to do a full survey or even suggest that you have a PCA-approved surveyor conduct a survey before they can give you a price:

• Extent of infestation: Larger and more established infestations require more intensive treatments - herbicide treatment may not be effective
• Removal method: Herbicide treatment is cheaper, but as the rhizomes (roots) will still be in the ground, you may have to repeat the treatment annually. Excavation and removal methods are more costly, but you may be able to get an insurance-backed guarantee that it has been eradicated
• Disposal costs: Proper disposal is necessary as Japanese knotweed is classified as controlled waste - it can’t be disposed of at your local tip
• Guarantees & insurance: If you have the knotweed fully removed, you should get an insurance-backed guarantee, but this is more expensive
• Property location: Urban areas, especially in the south east of the UK, tend to have higher costs. However, very remote areas may also see higher prices as it costs more for gardeners to travel from job to job

At HaMuch, we use our database of hourly and daily rates of gardeners across the UK to estimate the cost of Japanese knotweed removal. Find your nearest town or city in our cost table to get an idea of how much gardeners charge in your area.

How to identify Japanese knotweed

Japanese knotweed (Reynoutria japonica) is an invasive plant species known for its rapid growth and deep root system. It was introduced to the UK in the 19th century as an ornamental plant but has since become a widespread problem due to its aggressive spread. It’s now listed under Schedule 9 of the Wildlife and Countryside Act 1981, making it illegal to plant or cause Japanese knotweed to grow in the wild. 

Knotweed can grow up to 10cm per day during peak growing seasons, causing significant structural damage to buildings, roads and drainage systems. Underground, it forms a system of roots and rhizomes which can extend down 1 metre or more. Its resilience makes it difficult to eradicate without professional intervention.

Identifying Japanese knotweed early is crucial to preventing its spread and reducing removal costs. Key characteristics of the plant include:

• Bamboo-like, hollow stems with purple-red speckles, growing up to 2 metres tall. Early shoots have a pinkish colour
• Heart- or spade-shaped green leaves with a pointed tip, measuring 10-15 cm in length and arranged in a zig-zag pattern along stems
• Small, creamy-white flowers that bloom in late summer to early autumn
• Rapid growth, with new shoots emerging in early spring and forming dense clumps
• Extensive fibrous root system with thick, woody rhizomes that are often orange inside, capable of regrowing from tiny fragments

If you suspect you have Japanese knotweed on your property, it is essential to take action quickly by seeking professional identification and advice.

The impacts of Japanese knotweed on a property

Japanese knotweed can have serious financial and structural consequences for property owners. It can:

• Damage building foundations, walls and drainage systems, as it will grow into cracks and joints
• Reduce property value and deter potential buyers
• Make it difficult to secure a mortgage or home insurance
• Lead to legal disputes if the plant spreads to neighbouring properties

The value of the property

The presence of Japanese knotweed can significantly reduce a property's value. Some estimates suggest that properties affected by knotweed can lose 5-15% of their value or even more in severe cases. Even after removal, some buyers remain wary (especially if there isn’t an insurance-backed guarantee), so properties can take longer to sell.

Selling the property

Selling a property with Japanese knotweed can be challenging. Sellers are legally required to disclose its presence on the TA6 Property Information Form. Failure to do so can lead to legal action from buyers. Many buyers will negotiate a lower price or request a professional treatment plan with a guarantee before proceeding with the purchase.

Getting a mortgage

Many lenders are reluctant to approve mortgages for properties with Japanese knotweed unless there is an official treatment plan in place. Mortgage providers often require a professional management plan with an insurance-backed guarantee of at least 5 years to proceed with lending, though many lenders will assess each case individually.

Home insurance

Home insurance policies usually exclude damage caused by Japanese knotweed. Some insurers may refuse coverage entirely if knotweed is present on the property, although it’s rare. If you discover knotweed after purchasing a home insurance policy, insurers may require a professional treatment plan before renewing coverage.

How a gardener will remove Japanese knotweed

Not all gardeners will remove Japanese knotweed. Although not legally required, it’s a good idea to use a PCA-approved professional as they should have the right training and experience in dealing with knotweed.

Professional Japanese knotweed removal is typically carried out using one or more of the following methods:

Herbicide treatment

A cost-effective option, a chemical treatment is applied to the leaves to weaken and kill the plant. If there are other plants close by or other reasons why you want to limit the spread of the chemical, it can be injected directly into the stems.

While it seems like a cheap option, herbicide treatment can quickly become as expensive as excavation as it may take 3 to 5 growing seasons to completely eradicate the knotweed.

Excavation and removal 

Although it’s more expensive upfront, excavation and removal is the most reliable form of eradication. The gardener will dig out the entire root system, extending the digging area to around 2 or 3 metres past the visibly impacted area, and dispose of it at a licensed waste site.

Root barriers 

Root barriers are usually used as part of a Japanese knotweed management strategy rather than on its own. It involves burying a membrane or barrier into the ground, either vertically or horizontally, to prevent the spread of the knotweed’s rhizomes. 

How to dispose of Japanese knotweed

Disposing of Japanese knotweed is strictly regulated due to its invasive nature. The Environment Agency sets out how you must dispose of Japanese knotweed and other invasive non-native plants in a regulatory position statement (RPS):

• It must not be placed in general garden waste or taken to standard recycling centres/tips
• It should be disposed of at licensed landfill sites which have the correct type of permit that states they are equipped to handle invasive species
• If burning knotweed where it’s growing, you must ensure it’s completely dry and register a D7 waste exemption
• Transporting Japanese knotweed waste requires a waste carrier’s licence to prevent further spread
• Only bury it at the site where it was growing at a depth of 5 metres if it’s not sealed with a membrane, or 2 metres if it has been sealed

Can I remove Japanese knotweed myself?

While DIY removal is possible, it’s better to get a professional to do it because the plant is so resilient. Japanese knotweed’s roots can spread several metres underground, making it difficult to fully eradicate without professional treatment. Common DIY methods include:

• Cutting and burning: Cutting the plant down and incinerating it (where legally permitted) can slow its spread but does not kill the root system.
• Digging out: Attempting to dig out knotweed is extremely difficult as even a small piece of root can regrow into a full plant.
• Applying herbicide: While home-use herbicides can weaken the plant, professional-grade treatments are far more effective. You may have to use a home herbicide for 5 growing seasons before it’s eradicated.

How to prevent Japanese knotweed

Preventing Japanese knotweed from returning is essential to avoiding costly removal and legal issues. Here’s how you can reduce the risk:

• Early detection: Regularly inspect your garden and nearby areas for signs of knotweed growth
• Don’t spread contaminated soil: Avoid moving soil from areas where knotweed has been identified, as tiny root fragments can regrow.
• Be cautious when landscaping: Check new soil, plants or building materials for contamination before introducing them to your property.
• Create physical barriers: If knotweed is growing nearby, root barriers can help prevent it from spreading onto your land.
• Seek professional advice: If you suspect knotweed is growing on or near your property, consult a specialist before taking action.

By taking preventative measures, you can protect your property from the damage and financial impact caused by Japanese knotweed.

Given the legal and financial risks associated with ineffective removal, hiring a professional Japanese knotweed specialist is the safest and most effective option. Post your job on HaMuch now to get in touch with gardeners who can help you remove Japanese knotweed.

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