Japanese Knotweed And How To Treat It

Japanese Knotweed is an invasive and resilient weed. Its roots and rhizomes can grow to a depth of 2 metres. Even after herbicide treatment has “eradicated” the aerial and surface growth, the deep underground rhizomes can remain in a viable state and may do so for up to twenty years. It can re-emerge and re-grow on its own accord at any time and especially if the contaminated ground is disturbed.

If knotweed is left to grow untreated for a number of years it has the potential to cause damage to drains, paving, paths, driveways and poorly constructed boundary walls and will cause untold damage to buildings, foundations, pavements and even invade houses if they get in its way.

Able to grow up to 10 cm a day, Japanese Knotweed will target weak spots in buildings, cracked masonry, split pipes and ravage foundations if left unchecked.

Further issues that can arise from a Japanese knotweed infestation:

Issues with selling your property. Many mortgage lenders will not lend on properties affected by Japanese knotweed, and some may not lend if there is Japanese knotweed on neighbouring land.

Decrease in property value. Due to the stigma attached to this plant, a property’s value could decrease by as much as 25%, unless it is properly treated.

Legal liability. It is against the law to allow this plant to spread from one property to another. If your infestation has arrived from a neighbouring property then you could have legal recourse.

Treatments Available For Japanese Knotweed

Herbicide Treatment

This method provides cost efficient and effective control of Japanese knotweed and is ideal for homeowners, buyers and sellers.

Usually you will receive a comprehensive Knotweed Management Plan (KMP) which may include a detailed property survey, RICS risk assessment, knotweed distribution map and photographs. Japanese knotweed treatment works include herbicide treatment schedule, record of works, post-treatment monitoring and guarantee. If you’re selling your home, the KMP can usually be transferred to the new homeowners.

This treatment option is accepted by most UK mortgage lenders and provides you a 10 year KMP contract with Insurance Backed Guarantee.


Knotweed excavation provides instant eradication of Japanese knotweed. Ideal for:

  • Immediate complete removal of knotweed from a property.
  • Increasing sales potential for a property
  • Enabling property improvements: soft or hard landscaping, driveways, extensions.
  • Where long term herbicide treatment is not desirable.
  • Minimising negative impact knotweed can have on property value.

You will receive the same comprehensive KMP document. Treatment will involve the excavation of the knotweed and typically include bio-security controls, waste removal, root barriers, works records and re-instatement on completion with post-works monitoring and a guarantee of up to 10 years.

Guarantee insurance is also often an available option, with guarantees fully transferable to new property owners.

It is always wise to obtain a survey prior to purchase and Steven Stone is available to offer support and advice to clients. 

PHONE: 0203 925 3407 / 07796 363 006 
ADDRESS: 21 Ellis Street, Belgravia, London, SW1X 9AL. 
WEBSITE: www.stonesurvey.com  
EMAIL:   info@stonesurvey.com

Other blogs by Stone Survey: What To Do If Your Property Has Beetle Attack.
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