At SE Knotweed, Japanese knotweed is killed by an accredited glyphosate programme injected or applied across the growing seasons, or by excavation, because the rhizome survives a single quick treatment.
Killing knotweed costs from around £1,200 for a herbicide programme to £12,000 for full excavation, with the figure set by the size of the stand and whether the soil must be dug out and removed.
At SE Knotweed, Japanese knotweed is killed by targeting the rhizome that drives it, either with a glyphosate herbicide programme applied across the growing seasons or by digging the stand and rhizome out entirely. Cutting or strimming the canes does nothing lasting, because the plant regrows from the root system every spring.
The choice turns on your timescale and whether the soil can stay in place: herbicide is slower and cheaper, excavation faster and dearer. We confirm the method at survey, and the table below sets them against speed and relative cost. Get in touch and we will advise on the right approach for your stand.
Glyphosate does kill Japanese knotweed, but only over several seasons and applied correctly, because a single treatment weakens the top growth without killing a mature rhizome. Applied by stem injection or a foliar spray late in the growing season, the plant carries the herbicide down into the rhizome as it prepares for winter, which is when it is most effective.
A professional programme runs across 3 to 5 seasons with monitoring, using professional-strength glyphosate and the right timing rather than a stronger product. Our herbicide treatment page sets out the visit schedule, and the way it grows from the rhizome is why patience is needed.
Killing knotweed costs from around £1,200 for a herbicide programme on a small stand to £12,000 for full excavation on a large or awkward site, with the figure driven by the size of the stand, machinery access and whether the soil is dug out and removed as controlled waste. Herbicide is the lowest-cost route because the soil stays in place.
We measure the stand at survey and give a fixed price, and we often credit the survey fee against the treatment. The cost pillar breaks the figure down by method and size.
Killing knotweed by herbicide takes 3 to 5 growing seasons, because the rhizome has to be weakened treatment by treatment until it is dead, and the site is monitored to confirm no regrowth. Excavation removes the rhizome in a few days, so the plant is gone at once, though the ground is monitored afterwards for any missed fragment.
Where a sale is under time pressure, excavation or a root barrier keeps the ground usable straight away while the guarantee covers any regrowth. We give a realistic timeline with the plan rather than promising an unrealistic quick kill.
Excavation is the better way to kill knotweed when the ground must be clear quickly, when the stand is large or against a building, or when the plot is being dug for building work anyway. We dig out the stand and the contaminated soil and remove it under licence, so the rhizome is physically gone rather than treated in place.
It is the fastest method and the most expensive, from around £4,000 to £12,000, because the soil is controlled waste with disposal and gate fees. Our excavation page explains the process, and on-site relocation offers a cheaper route where the soil can be buried on the plot.
Knotweed will not die from cutting or covering because both leave the rhizome alive, and the rhizome is the plant. Cutting or strimming removes the canes but scatters fragments that each grow into new stands, and moving the cut material spreads it further, so it usually makes the problem worse.
Covering with a membrane suppresses top growth but a mature rhizome survives beneath it and can travel sideways for years, so it contains rather than kills. This is why a proper kill needs either herbicide into the rhizome or physical removal, and why DIY attempts so often fail.
| Method | Speed | Relative cost | Best for | Soil / waste | Guarantee |
|---|---|---|---|---|---|
| Herbicide treatment | 3 to 5 seasons | Lowest | No sale deadline, soil can stay in place | Minimal | Insurance-backed |
| Excavation and disposal | A few days | Highest | Fast clearance and development plots | Soil removed under licence | Insurance-backed |
| On-site relocation (cell burial) | 1 to 2 weeks | Medium to high | Larger sites keeping soil on the plot | Buried on site to a cell | Insurance-backed |
| Root-barrier membrane | Days | Medium | Containing spread at a boundary | Minimal | Situational |
| Combination treatment | Varies | Medium | Mixed or access-restricted sites | Varies | Insurance-backed |
Tell us the address and what a surveyor flagged. We confirm the plant, record the RICS category and set out the figures.