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Your Guide to Japanese Knotweed

Your Guide to Japanese Knotweed

Japanese Knotweed is a flowering plant that was first introduced to Britain from the Far East in the 19th century. It was noted for its attractive appearance and planted as an ornamental plant. In Japan its growth was kept under control by indigenous insects (Aphalara Itadori), which do not exist in the UK.

The plant is a high risk due to its invasive nature and un-formidable rate of growth. The Knotweed can grow up to a staggering 10cm a day when left to grow, destroying whatever it finds in its path, including brickwork, cavity walls, sewage systems, concrete slabs and driveways. If the shoots or stem penetrate then its rate of growth will continue to increase while it works its way through the area, leading to significant damage.

To an experienced eye the plant is unmistakable, however to an untrained person it can be easily overlooked or mistaken for a variety of other plants such as Pheasant berry of a young bamboo plant. The key characteristics of the plant are:

  • Heart shaped leaf which vary is size depending on age
  • A purple/red stem with a zig-zag pattern
  • The stem is very similar to bamboo however there are usually purple specks.
  • The foot of the stem grows partially above ground and often various other parts of the roots will be visible.
  • When in bloom the flowers are white and grow in clusters.


Photograph taken by Ray Smith, Senior Partner and Chartered Surveyor at Watsons.

If Japanese Knotweed is found on or near your property it can cause serious problems. It is estimated by the government that to completely eradicate the plant it will cost£1.25 billion. It is more common than many people believe with some experts estimating that there is not a 6 square mile section of the UK that doesn’t contain the plant.

If you are living in a property and Japanese Knotweed has been found, the most important thing is to leave the plant alone. If the plant is disturbed it can significantly delay the treatment and also means any warranty from the treatment contractor will be invalid. Under the Wildlife and Countryside Act 1981 it is an offence to plant or cause Knotweed to spread in the wild. All waste containing Japanese Knotweed comes under the control of Part 2 of the Environmental Protection Act 1990 and must be properly disposed off as it classed as controlled waste. This means all waste must be taken to a licensed premises or it can lead to prosecution.

There are many home owners trying to deal with Japanese Knotweed and also many contractors who are experts in the treatment of the plant. If you are hoping to purchase a property but the survey has found Japanese Knotweed in the property it is important to choose a PCA approved contractor. The more common Knotweed becomes, the more mortgage lenders are willing to offer mortgages when a PCA member contractor is in place. These specialist contractors have the ability to follow up the agreed work with a guarantee, so the lender is at minimal risk.

If a Chartered Surveyor carries out a survey such as a RICS HomeBuyer Report or a Full Building Survey and finds Knotweed, it is common for the mortgage lender to ask for a specialist report to be commissioned at the expense of the property vendor. The report will categorise the property on the RICS scale and explain how the Knotweed will need to be treated. The mortgage lender and potential buyer will then decide whether to proceed with the sale. By ensuring a survey is carried out at the beginning of the process, if there are any issues the delays will be reduced.

If you would like more advice about a pre-purchase survey or to discuss an property containing Japanese Knotweed please contact our survey department on 01603 751577 or email


Mark Francis Pearce

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