Japanese Knotweed (Fallopia japonica) has become the UK’s most invasive species. Its speed of growth, structural damage, and resilience are problems for property owners and developers alike. As the problem grows, so does the need to choose the best and most cost-effective solution.
Two methods are regularly used for Japanese Knotweed removal: herbicide and excavation. Each has its costs, benefits and scenarios where one is more suitable. This article will compare the costs of both to help property owners and managers make informed decisions.
Find out more Japanese knotweed removal cost by clicking here.
Herbicide Method
Process
Herbicide treatment involves applying specialist chemicals to Japanese Knotweed. Multiple treatments over several growing seasons are required to kill the plant and its extensive root system.
Costs
- Initial Survey and Assessment: Before treatment starts, a professional survey is required to determine the extent of the infestation. This costs between £200-£800 depending on the site size and complexity.
- Herbicide and Application Equipment: The cost of herbicides and application equipment varies depending on the size of the infestation.
- Labour Costs for Multiple Treatments: Professional herbicide application requires 1-3 treatments per year over 3-5 years.
- Monitoring and Follow-up Treatments: Regular monitoring is required to check that the treatment is working.
Time to Work
Herbicide treatment is a long-term solution: 2-5 years of continuous treatment to kill Japanese Knotweed. This is because the plant has stored nutrients in its extensive rhizome system.
Additional Costs
- Re-treatment due to regrowth or missed areas
- Environmental testing to check that there is no lasting impact on soil or nearby water sources
- Disposal of dead plant material (if required by local regulations)
Excavation Method
Process
Excavation involves physically removing the Japanese Knotweed and its root system from the affected area. This method requires heavy machinery and is more invasive but can give quicker results.
Costs
- Initial Survey and Assessment: Similar to herbicide treatment, a professional survey is required, costing between £ 200 and £400.
- Heavy Machinery Rental or Purchase: Excavators and other equipment can cost £200-£500 per day to rent or more if purchased.
- Labour Costs for Excavation and Disposal: Skilled operators and labourers are required. Costs will vary depending on the site’s complexity.
- Transport and Disposal Fees: Removed Knotweed must be disposed of at licensed facilities. Cost, including transport, can be £50-£200 per tonne.
- Site Restoration Costs: After excavation, the site will need to be restored. The cost will vary depending on the extent of the excavation and the finish required.
Time to Complete
Excavation can be done quickly, usually within a few days to a week for most domestic properties. Larger infestations or complex sites may take longer.
Additional Costs
- Unexpected underground obstacles requiring specialist equipment
- Deeper than expected root systems requiring more excavation
- Soil contamination requiring a larger area to be treated
Herbicide vs Excavation Cost Comparison
Upfront Costs
Herbicide treatment has lower upfront costs than excavation. An initial herbicide treatment programme will cost between £2,000-£8,000 for a typical domestic property. Excavation can cost £10,000+ depending on the size of the infestation and site.
Long term Costs
Herbicide treatment has lower upfront costs, but multiple treatments over several years will add up.
Excavation has higher upfront costs but is often a one-off. If not done properly, it will require follow-up treatments, which will increase the overall cost.
Return on Investment
When considering the return on investment, you need to factor in the time value of money and the opportunity costs of each method (if you have a commercial site and want to find out more click here). Excavation has higher upfront costs but may be more cost-effective for properties that need to be Knotweed-free quickly, e.g., development projects or property sales.
Herbicide treatment, with its lower upfront costs, may be more suitable for properties where immediate eradication is not critical and can be spread over several years.
Scenarios Where Herbicide Treatment is More Cost-Effective
Herbicide treatment may be more cost effective in the following scenarios:
- Small to Medium Infestations: For localised Knotweed problems, herbicide treatment is a more economical solution.
- Difficult Access Sites: Herbicide treatment is a more viable option where heavy machinery can’t access the affected area.
- Environmentally Sensitive Areas: Near water sources or protected habitats, carefully applied herbicides may have less of an environmental impact than extensive excavation.
- Budget Constraints: The lower upfront costs of herbicide treatment are more manageable for those with limited immediate funds.
- Long-term Property Plans: A longer timeframe for herbicide treatment may be acceptable for properties that will not be developed or sold in the near future.
Scenarios Where Excavation is More Cost Effective
Excavation may be the more cost effective option in the following scenarios:
- Large Infestations: For extensive Knotweed problems, the speed and thoroughness of excavation outweigh the higher costs.
- Time-Critical Projects: When Knotweed needs to be removed quickly, e.g., for imminent construction projects, excavation gives quicker results.
- Total Eradication Required: Where total Knotweed removal is necessary, e.g. for property sales or legal compliance, excavation gives more immediate and definitive results.
- High-Risk Spread Areas: Where Knotweed is an immediate threat to neighbouring properties or infrastructure, swift removal through excavation may be preferable.
- Planned Excavation for Other Reasons: If the site already needs excavation for construction or other reasons and Knotweed removal can be done at the same time, it can be cost-effective.
Cost Effectiveness Factors
Several factors will influence which is more cost effective (click here for a more in-depth Japanese Knotweed Cost Factor guide):
- Size and Density of Infestation: Larger, denser infestations may make excavation more cost effective as herbicide methods require multiple treatments over several years.
- Site Accessibility: Difficult access sites will increase excavation costs significantly, making herbicide treatment more economical.
- Legal Regulations and Disposal Options: Strict legal regulations on herbicide use or limited access to licensed disposal facilities will impact the cost effectiveness of each method.
- Property Value and Intended Use: The higher upfront costs of excavation may be justified for high value properties or properties being developed soon.
- Risk of Spread: Properties, where Knotweed is an immediate risk to neighbouring areas, may benefit from the quick solution of excavation even though it’s more expensive upfront.
Deciding between herbicide treatment and excavation for Japanese Knotweed removal can be tough. While herbicide treatment has lower upfront costs and is less invasive, excavation gives quicker results and may be more cost-effective in the long run for certain scenarios.
The size of the infestation, site conditions, time constraints, and future property plans all come into play. It’s clear there’s no one-size-fits-all solution, and each case needs to be judged on its merits.
We believe professional assessment is key to finding a cost-effective solution for Japanese Knotweed removal. As experts in this field, we can give you site-specific advice based on your site conditions and the latest treatment methods to give you the most economical and effective solution for your situation.
