weeds
Japanese knotweed treatment and removal
£1,500 to £3,000 covers a herbicide programme on a small domestic stand, run across three to five years. Excavation and removal off site starts near £4,000 and passes £20,000 on larger plots. A specialist survey costs from £250 plus VAT.
What this covers
What it costs. Method and infestation area drive the figure, and the gap between the two main routes is enormous. Full cost breakdown.
What the job covers
- Identifying knotweed and mapping its extent
- Herbicide programmes over several seasons
- Excavation and removal where time is short
- Management plans for a sale or a mortgage
- Disposal at a permitted site with the paperwork
Worth knowing
Japanese knotweed, and soil within seven metres of it, is controlled waste. It cannot go in a garden waste bin or to a recycling centre, and whoever moves it must be a registered carrier taking it to a permitted site.
Environmental Protection Act 1990, Part II
What is involved
Herbicide is the route most gardens take. Stem injection and foliar spray applied one to three times a year, timed from late summer so the chemical travels down into the rhizome, will usually kill a stand over three to five years. Contractor prices for a stand under 50 square metres cluster at £1,500 to £3,000, and a cost guide quoting £500 sits well below every specialist checked. Excavation is the fast alternative and the expensive one, with full dig and disposal running £4,000 to £20,000 on a domestic plot and far higher on large sites.
Ownership carries no offence in itself. Planting knotweed or causing it to grow in the wild is an offence under section 14 of the Wildlife and Countryside Act 1981, and letting it spread onto a neighbour's land opens a private nuisance claim, settled in Network Rail Infrastructure Ltd v Williams in 2018 on the basis that encroaching rhizome burdens the land before any physical damage appears.
Waste rules apply the moment the plant is dug. Soil and plant material carrying knotweed is controlled waste, must travel with a registered carrier and must reach a permitted landfill, at £50 to £200 a tonne including transport. On site burial is allowed at five metres depth, or two metres under a sealed geotextile membrane, with the Environment Agency notified in advance. Anyone spraying must hold a certificate of competence for herbicide use or work under the direct supervision of someone who does.
Choosing someone for the job
Is the contractor a member of the Property Care Association or INNSA, and what is the membership number? Which method is proposed, and why that one for this site? How many years does the treatment plan run, how many visits a year, and what monitoring follows? Does an insurance backed guarantee come with it, for how long, and who underwrites it? Which certificates of competence do the sprayers hold?
Common questions
Is Japanese knotweed illegal to have in a garden?
Having it is not an offence and there is no duty to remove it unless it causes a nuisance. Planting it or causing it to grow in the wild is an offence, and letting it cross a boundary can lead to a civil claim from the neighbour.
Will knotweed stop a mortgage?
Lenders rarely refuse outright. Most want a survey, a management plan from a certified specialist and an insurance backed guarantee, usually ten years, with retentions more likely where a surveyor records RICS management category A or B.