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Japanese Knotweed

Andrew Boast

07/07/2017

Japanese Knotweed is classified as one of the most destructive non-native invasive species in the UK by the Invasive Non-Native Specialists Association (INNSA). The environment agency refers to it as 'the UK's most aggressive and destructive invasive plant' and the Environmental Protection Act 1990 classifies it as ‘controlled waste’.

Click if you're just looking for the Japanese Knotweed Heat Map or simply scroll down this article.

The plant spreads and grows prodigiously and can break through concrete and brickwork. It is an invasive and resilient weed which can grow up from deeply rooted rhizomes and reappear again many years after it has been treated. If it is present in your property and you don’t take action, then it can devastate buildings and landscaping on both yours and your neighbour’s properties. Read on to find out more about this devastating plant.

Japanese Knotweed - a live and ongoing concern

Recent media reports frequently refer to Japanese Knotweed devastation and its effects - click on the following link to read about how someone has objected to a development in West Howe in Bournemouth because the area apparently was infected with Japanese Knotweed and cleared in 2018

If you're buying a property, we'd always advise getting a RICS Home Buyers Survey (whether a HomeBuyer Report or Building Survey) as a general precaution. Our expert nationwide RICS surveyors are trained to spot suspicions of the most destructive property defects, such as subsidence and rising damp and this includes looking for signs of Japanese Knotweed infestation.

Buying a house? Worried about defects including Japanese Knotweed?

Get a RICS Home Buyers Survey to put your mind at rest. Our expert RICS surveyors conduct a thorough inspection of the property and grounds, looking for any suspicions of defects and issues then call you on the day of the survey after the inspection to summarise their findings.

Often, it is the RICS surveyor's report on a house which gives the first alert to a potential buyer of the presence of Japanese Knotweed.

Your survey report is delivered both email and Royal Mail within 5 working days.

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NB Click if you require a specific Japanese Knotweed site survey or call 0333 344 3234

There are additionally Japanese Knotweed insurance policies that buyers can take out before they buy their home, however there are strict criteria needed to be met in order for you to make a claim. The cost of this insurance is from £60 and it can be ordered by calling 0333 344 3234 (local call charges apply).

How do you spot Japanese Knotweed?

The leaf is very distinctive, but still can be confused with other common plants. For many, the safest solution is to get a RICS surveyor to attend their property as they conduct a RICS HomeBuyer Report or a Building Survey. We have local surveyors throughout England - Call us on 0333 344 3234 if you want to inspect your property or confirm if you have Japanese Knotweed.

You can order an insurance policy to help protect you and your mortgage lender in the event that Japanese Knotweed is identified on the property within 5 years of owning. This highly affordable insurance is provided by CLS Risk Solutions and covers properties of up to 0.5 acres (larger properties quoted on application). It covers up to £20,000 towards financial loss if Japanese Knotweed is found at the property. The policy is designed to be 'consumer friendly' i.e. it limits exclusions and conditions of claims. Click here to read a Japanese Knotweed Indemnity Policy.

What if you have a mortgage?

Mortgage lenders are known to be extremely cautious about lending mortgage monies if the plant is detected. If during your mortgage valuation survey the surveyor spots signs of Japanese Knotweed, then they will report this to your mortgage lender. The mortgage lender will most likely refuse to lend you the mortgage without the weed being treated and removed prior to completion.

What is Japanese Knotweed?

Japanese Knotweed (Fallopia japonica) is a tall, fast-growing Japanese plant of the dock family and has bamboo-like stems and small white flowers. It was originally brought to the UK, in the mid-19th century, because of its beauty - with red stems and deep green leaves - but it has become a scourge for home owners.

It can grow up to 20cm every day and its roots can go down to 3m deep. It can grow through concrete and tarmac and it has no natural predators. It swamps other plants, denying them light. Although it produces no seeds, it can grow from the tiniest fragments of rhizomes, which are the underground network of stems and roots.

How do I know if I have Japanese Knotweed?

The plant starts growing from early spring and can reach 1.5m by May and 3m by June. It dies back between September and November. Its signs are:

fleshy red tinged shoots when it first breaks through the ground
large, heart or spade-shaped green leaves
leaves arranged in a zig-zag pattern along the stem
a hollow stem, like bamboo
dense clumps that can be several metres deep
clusters of cream flowers towards the end of July that attract bees
dies back between September and November, leaving brown stems

How much can Japanese Knotweed cost in damage?

Japanese Knotweed costs the UK economy £166 million per year for treatment and because of devaluations, according to one source.

A London couple were advised that it would be cheaper to knock down their £300,000 home rather than treat it. One lady who was originally told her Swansea home was worth around £80,000 was subsequently advised that, because of the untamed plant, it would not be worth more than £45,000.

How at risk of Japanese Knotweed are you?

A property is considered as being affected by knotweed if it is found within the boundaries of the property or close to the property boundary on an adjacent property. To help understand and categorise the level of risk that the knotweed presents to the property, the Royal Institution of chartered surveyors (RICS) have created a "risk" table (see diagram on the left). The area around the knotweed is referred to as the "risk zone" and its location in relation to the buildings should be formerly recorded and the risk category accurately assessed.

Japanese Knotweed Removal

Japanese Knotweed Removal should be handled by professionals because of how extensive the problem can become and the issue of removing and destroying all traces of the plants' rhizomes. Please read Japanese Knotweed Removal to find out more.