What to Do If You Suspect Japanese Knotweed on Your Property
If you suspect the presence of Japanese knotweed on your property—or if a valuer raises concerns—you should arrange a professional Japanese knotweed survey without delay. Early detection is crucial to avoid legal, structural, and financial complications.
Why You Need a Professional Knotweed Survey
A survey must be carried out by a qualified and accredited firm, specifically one that is a member of the Property Care Association (PCA). These specialists are trained to identify, assess, and provide guidance on invasive species like Japanese knotweed.
What the Survey Includes
A professional Japanese knotweed identification report will typically include:
Confirmation of the presence or absence of knotweed
The precise location of the infestation (on or near the boundary)
The extent and severity of the risk
Recommended remediation or treatment plans
This report is essential if you're buying, selling, or developing land, as it can affect property value and mortgage approvals.
Cost of a Japanese Knotweed Survey
Some companies offer free knotweed surveys, especially if treatment is later commissioned through them. However, it's common for a fee to apply if no evidence of knotweed is found.
Japanese Knotweed Management Plan for House Buying and Selling
If a property shows evidence of Japanese knotweed, a formal Knotweed Management Plan is usually required—especially during the house buying or selling process. Most UK mortgage lenders insist on having a verified management plan in place, particularly when the infestation is within the property boundary. In some cases, even knotweed present nearby or on adjacent land can trigger this requirement.
Why a Knotweed Management Plan Is Essential
A Japanese knotweed treatment plan demonstrates that the invasive plant is being professionally managed and controlled. Without one, securing a mortgage can be difficult, and a property’s value may be negatively impacted.
Duration and Guarantee Requirements
Treatment plans typically range in duration:
5, 7, 10, or 15 years, depending on the severity
Most come with an insurance-backed guarantee
Mortgage lenders often require a minimum 10-year guarantee to approve the plan
This ensures long-term monitoring, professional remediation, and peace of mind for buyers, sellers, and lenders.
Costs of Knotweed Treatment
The cost of a knotweed management plan can vary widely based on:
The extent of the infestation
The type of treatment required (chemical vs. excavation)
The length of the guarantee
In many cases, the cost can run into several thousand pounds.
Herbicide Treatment for Japanese Knotweed: What You Need to Know
One of the most common and cost-effective methods for treating Japanese knotweed is the application of chemical herbicides. This approach is typically used over a long-term period to suppress and prevent regrowth of the invasive plant. However, full eradication can take several years, depending on the severity and spread of the infestation.
Factors Affecting Herbicide Selection
The type of herbicide and treatment method used will depend on several site-specific factors, including:
Size and density of the knotweed infestation
Nearby vegetation, such as trees, shrubs, or protected plant species
Proximity to water sources, like rivers, streams, ponds, or the sea
Local wildlife habitats that may be affected by chemical use
These variables must be carefully considered to ensure safe and effective treatment.
Why Professional Application Is Essential
Herbicides should only be applied by trained professionals who hold a valid National Proficiency Test Council (NPTC) Certificate of Competence. Using a qualified contractor ensures:
Safe and legal use of chemicals
Proper dosage and application methods
Compliance with environmental regulations
DIY treatment is strongly discouraged, as improper use can worsen the infestation and damage the surrounding ecosystem.
When Herbicide May Not Be Suitable
If you plan to disturb the ground—for example, by planting, building a cabin, installing a hot tub, or undertaking other landscaping or development—herbicide treatment may not be appropriate. Disturbing treated soil can reactivate dormant roots and cause regrowth. In such cases, excavation and removal of contaminated soil may be the better long-term solution.
Excavation as a Japanese Knotweed Removal Method
When herbicide treatment is either ineffective or unsuitable due to site conditions, excavation may be the most effective method for removing Japanese knotweed. This process involves physically digging out the affected soil to a specified depth, ensuring full removal of the plant and its extensive root system (rhizomes).
When Is Excavation Recommended?
The knotweed infestation is extensive or deeply rooted
The site will be developed or disturbed (e.g., for building foundations or landscaping)
Herbicide use is not feasible due to proximity to water, wildlife, or sensitive plants
How Excavation Works
Contaminated soil is dug out and removed, typically to a depth of 2–3 meters
The soil is classified as controlled waste under UK environmental law
It must be handled by a licensed waste removal company
Disposal must take place at an approved landfill site, subject to Landfill Tax and transport costs
Not all landfill facilities accept knotweed-contaminated soil, and availability can significantly impact disposal costs.
On-Site Burial as a Sustainable Alternative
For large development sites, a more sustainable approach may involve burying the contaminated soil on-site in a designated, contained area. This method is typically used by:
House builders or property developers with spare land
Projects requiring deep foundations, allowing space for controlled burial
Sites where excavation is already part of the building plan
In these cases, the excavated area is often sealed with a non-permeable membrane to prevent regrowth.
Expert Survey and Recommendations
Before choosing a treatment method, a professional Japanese knotweed survey is essential. A qualified surveyor will assess the infestation and recommend the most appropriate solution, whether that’s herbicide treatment, excavation, on-site burial, or a combination.