Japanese knotweed is an invasive plant species that poses a significant threat to properties and landscapes across the UK. Homeowners and developers often wonder about the costs associated with treating or removing this troublesome plant. The answer, as many Japanese knotweed companies will tell you, is not straightforward—it depends on various factors. In this article, we will delve into the intricacies of knotweed removal costs, drawing insights from Environet’s own experience and data collected from quoted projects. 

Factors influencing Japanese knotweed removal cost

The cost of removing Japanese knotweed is affected by a whole host of factors, which is why it is imperative that a professional survey is undertaken to establish all the parameters prior to deciding the best option for your project. When you ask a professional for a Japanese knotweed removal price, the following factors will determine the removal cost.

1. Treatment Method:

Various methods are available for Japanese knotweed treatment, each with its associated costs. The type of treatment or removal will primarily be determined by the desired outcome and future land use. Depending on the method chosen, 5m² of knotweed will cost between £3,000 and £12,000.  

Herbicide Treatment is normally the cheapest method but is typically regarded as a form of “control” rather than removal due to the risk of regrowth. Investing less to control knotweed may be a good option if you are keeping the property long term – however research shows you are likely to secure lower offers for your property when it comes to selling on account of the residual inconvenience and risk to the buyer. Diminution in property value is one of the biggest hidden costs of Japanese knotweed herbicide treatment.  

Excavation and Disposal at Landfill (Dig & Dump) is normally the most expensive option and can be between four and ten times the cost of herbicide treatment.  

On-Site remediation such as Screening, Stockpile and Treat and On-Site Burial can offer cost savings of at least 40% compared to Dig & Dump. However, their feasibility depends on site conditions. In gardens, on site remediation like our bespoke DART™ or Resi-Dig-Out™ service provide great value knotweed removal with plans starting from around £4,000.   

Our Xtract™ method for commercial sites starts from £10,000 and can provide savings of at least 50% compared to Dig & Dump. 

2. Quantity of Infested Land:

The quantity of land infested with Japanese knotweed is the secondary determinant of treatment costs. Generally, the greater the area affected the higher the cost will be. As knotweed spreads year by year, delaying treatment may lead to escalating costs. The longer it is left unmanaged, the greater the chance that it will be accidentally spread, or worse, enter neighbouring properties or cause damage to overlying structures – adding to the complexity and overall removal costs.  

3. Site-Specific Conditions: 

Site conditions play a crucial role in determining the most effective and cost-efficient treatment method. Variations in knotweed maturity, rhizome depth, lateral spread, and ground type can impact costs.  

The ease of access to the infested area is also a practical consideration. Limited access may necessitate additional measures, such as the installation of temporary surfaces or the lifting of machinery over walls – adding to the overall cost of Japanese knotweed removal. 

Treatment costs can vary by region due to differences in local regulations, labour costs, and availability of specialised equipment. 

4. Guarantee Requirements: 

Different treatment methods may have varying guarantee requirements, affecting the overall cost. The quality and duration of any guarantee needs to be carefully considered, especially where the property is being sold. 

A robust guarantee is essential when selling a property affected by Japanese knotweed to ensure the saleability. Most financial institutions will require a treatment/removal program with an insurance-backed guarantee (IBG) of 10 years. 

Potential Pitfalls and Additional Costs 

It’s important to be vigilant about potential pitfalls and additional costs associated with Japanese knotweed treatment: 

1. Incorrect Estimation of Soil Volume: Low prices for Dig & Dump may result from incorrect estimations of infested soil volume. Always verify that quotes are based on accurate measurements.
2. Disposal at Illegal Sites: Improper disposal of knotweed at illegal sites poses legal risks. Ensure that your chosen knotweed contractor complies fully with the “duty of care” requirements.
3. Incorrect Landfill Tax Rates: Avoid the temptation to dispose of topsoil at standard tax rates, as this is illegal.
4. Incomplete Excavation: If excavation is incomplete and viable rhizome remains in the ground, further treatment or excavation may be required. Also ensure that the price quoted is for full excavation and is not capped at a set depth. 

Economic Considerations

For developers, timing is crucial, as delays in resolving the knotweed issue can have cascading effects on subsequent construction phases. While working closely with a knotweed specialist can mitigate programmatic issues, it’s important to remember that expedited removal comes with higher costs. 

Conclusion

Understanding Japanese knotweed treatment costs requires careful consideration of various factors, including the quantity of infested land, treatment methods, site-specific conditions, and accessibility. By being aware of potential pitfalls and additional costs, property owners and developers can make informed decisions to effectively manage and mitigate the impact of Japanese knotweed on their properties and investments. 

*NB: figures based on 2023 prices and exclude VAT