Does DIY Treatment Work on Japanese Knotweed?
From our previous blog, you’ll already know what Japanese Knotweed is and why it’s considered one of the most difficult plants in the UK to eradicate. Its deep root system and aggressive growth make it incredibly resilient, which is why so many DIY attempts fail.
There are a lot of myths and misconceptions about how to deal with Japanese Knotweed. From DIY fixes to ‘home remedies’, people often try quick solutions that don’t work and in some cases can actually make the problem worse.
This blog details some of the questions and methods that SE Environmental have come across people using over the years and explores their effectiveness or often lack of!
Can I Treat Japanese Knotweed With Bleach?
No. Soaking Japanese Knotweed roots in bleach can technically kill them, but simply spraying or pouring bleach on the soil won’t reach the rhizomes and is largely ineffective. Doing so can also damage surrounding soil, harm nearby plants, and may breach environmental legislation — tipping chemicals into the ground without proper control is illegal. Knotweed almost always comes back if not treated professionally, and improper DIY attempts can make the problem worse.
Can I Treat Japanese Knotweed With Salt or Boiling Water?
No. Salt and boiling water may scorch surface growth, but they don’t reach the rhizome (root system.) These methods can damage soil health, harm other plants, and disposing of large amounts of salt or water onto soil could breach environmental regulations. Using these methods may push the knotweed into dormancy, making it harder to treat properly.
Can I Treat Japanese Knotweed With Vinegar?
No. Vinegar is a preservative — not an effective herbicide. It doesn’t penetrate the deep root system and leaves behind long-term damage to the soil. Vinegar is not an effective herbicide and doesn’t penetrate deep roots. Pouring it onto soil can leave long-term damage and, like other chemicals, may breach environmental laws if disposed of carelessly. Vinegar treatment is unlikely to eradicate knotweed and can harm the surrounding ecosystem.
Can I Treat Japanese Knotweed With Weedkiller From a Garden Centre?
No. Consumer-grade weedkillers aren’t strong enough to kill knotweed. Incorrect dosage, timing, or weather conditions can allow the plant to survive in a “bonsai” growth form, making future treatment more difficult. Excessive or improper use of herbicides can also breach environmental regulations and damage the surrounding ecosystem.
Can I Dig It Up Myself?
No. Digging knotweed is rarely successful. Even tiny fragments (as small as 0.5g) can regrow, potentially spreading the infestation further. Incorrect disposal of contaminated soil is illegal and can result in fines or prosecution.
Can I Burn It or Cover It With Tarps, Plastic or Concrete?
No. Covering knotweed forces it to spread sideways until it finds a way out — often leaving you with a bigger problem than before. Burning removes stems temporarily, but roots remain alive underground. In some cases, knotweed has reappeared more than a decade later after being “covered up.”
Do DIY Methods Work?
The short answer is: no. SE Environmental regularly receives calls from homeowners who have tried chemicals, home remedies, or other quick fixes — and without exception, these attempts have failed. In many cases, they’ve actually made the problem worse.
Home remedies and DIY methods are not recommended for treating Japanese Knotweed for several reasons. While contractor-grade glyphosate-based herbicides are widely regarded as the industry standard for controlling perennial weeds — including Japanese Knotweed — they must be industrial, controlled, and applied by licensed professionals. These herbicides break down in the soil and leave no long-term effects. Bleach, salt, and vinegar, on the other hand, can have lasting and unpredictable effects on both the soil and surrounding plants.
We often get enquiries from people who have tried to treat knotweed themselves using garden-centre herbicides or other unconventional methods. Without exception, these attempts fail and often make the problem worse.
This is because anything other than contractor-grade herbicides — applied at the correct dosage, dilution, timing, and under suitable weather conditions — can cause the plant to enter a state of dormancy. In other words, the plant senses unfavourable conditions and reduces its growth. This dormancy can last years, sometimes leaving no visible stems or leaves, only for the plant to re-grow later, often during landscaping works.
A common sign of poor treatment is “bonsai” growth, where stems are only a few centimetres tall with tiny leaves. At this stage, very little herbicide can penetrate the plant to reach the roots, making it extremely difficult to treat. Other considerations, such as Environment Agency permits and ecological impacts, also make DIY approaches risky.
Covering the infestation with plastic membranes or even concrete is also ineffective. The knotweed either spreads sideways, enlarging the infested area, or goes dormant beneath the barrier, sometimes re-emerging up to 15 years later.
It’s also illegal to conceal Japanese Knotweed when selling a property. The TA6 property form specifically asks whether knotweed is present, absent, or unknown. Failing to declare it can result in penalties far higher than the cost of proper treatment, including estimated property devaluation and remediation costs.
Clearly, this isn’t a matter of going to a hardware store, buying pre-mixed herbicide for block paving, and giving it a spray. Excavation is a method we routinely use to quickly eradicate infestations, but it’s far more complex than digging up a root. Every tiny fragment — as small as 0.5g, about the size of a fingernail — must be removed to prevent regrowth.
Once excavated, the knotweed often needs to be stockpiled and transported to a registered landfill site. These sites only accept soil that has been tested for contaminants such as asbestos, heavy metals, or hydrocarbons, making the process highly controlled.
How Can You Actually Treat Japanese Knotweed?
Treating Japanese Knotweed really is a job for the professionals, and for several reasons.
Firstly, identifying and accurately mapping Japanese Knotweed isn’t as simple as it may seem — particularly with immature infestations or plants that have already been subject to DIY treatments, which can make stems and leaves look different from healthy plants. A thorough survey is essential to determine the full extent of the plant, including its root and rhizome system. The survey also identifies potential ecological considerations, such as nearby watercourses or wildlife, that could be impacted by the treatment.
Once the survey is complete, a qualified technician can outline the benefits and drawbacks of the different treatment options, including herbicide application, excavation and disposal to registered landfill, cell burial, and stockpiling with ongoing treatment.
Herbicide Application
For most domestic situations, professional herbicide application is the preferred method. It is less disruptive, usually has minimal access restrictions, and is often the most cost-effective solution — typically around £2,000 + VAT for a standard garden.
The downside is that it can never be officially guaranteed that the Japanese Knotweed is completely dead. There is always a small chance of regrowth, and several years of monitoring and repeated treatments are usually required.
Excavation and Disposal to Landfill
Excavation can be an option when rapid eradication is required, but it is far more complex than simply digging up the roots. Every fragment — even as small as 0.5g — must be removed, or it can regrow. Excavated material is then often transported to a registered landfill, which may require chemical analysis to ensure soils are free from contaminants such as asbestos, heavy metals, or hydrocarbons.
In domestic gardens, excavation can be complicated if the roots extend under fences, sheds, patios, or decking. Large-scale excavations are typically only feasible on development sites where machinery can access the area, and there are no obstructions to removing contaminated soil.
Cell Burial
Cell burial is a technique used on large sites where certain areas are left undisturbed indefinitely. It involves creating a cell lined with a root-barrier membrane, filling it with knotweed-contaminated soil, sealing it, and covering it with 2–3 metres of topsoil. Holes can exceed 6 metres in depth, requiring careful excavation to prevent collapse.
This method can be more environmentally friendly than landfill disposal, as it reduces waste volume and transportation distances, potentially lowering the carbon footprint of a project.
Stockpiling and Ongoing Herbicide Treatment
Another approach for large sites involves excavating and stockpiling the knotweed in an undisturbed area for at least five years. Any regrowth can then be treated with herbicide. Excavation and stockpiling break up the rhizome structure, creating multiple smaller plants that are easier to treat than a mature infestation in situ. This method is often used when knotweed is near a time-critical part of a development, or when landfill disposal is not viable due to cost or environmental considerations.
Why You Need a Professional
While it is legally possible to treat Japanese Knotweed yourself, without the correct herbicide licenses you cannot legally purchase or apply the products required to do so effectively. Without training, it’s highly unlikely that the application timing, dosage, and method will be correct, often making the problem worse.
Mortgage lenders, councils, and other authorities only recognise treatments carried out by a PCA Certified Surveyor in Japanese Knotweed (CSJK). Without a qualified professional, a property may not be approved for mortgage or sale, regardless of any remediation work attempted.
Take Action Against Japanese Knotweed
Don’t risk making Japanese Knotweed worse with DIY methods or ineffective products. Protect your property and secure mortgage approval by getting professional, accredited treatment. Contact SE Environmental today for a survey and approved management plan — and take the first step to permanently tackling Japanese Knotweed
