Japanese knotweed: removal, identification and treatment

As a Japanese knotweed invasion threatens one woman’s three-year home restoration project, we outline what this insidious plant is and how you can treat it

A homeowner’s dream renovation project hangs in the balance, as an infestation of Japanese knotweed threatens to take over the home she has spent more than three years restoring. 

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Chronicle Live recently interviewed Tina Richmond, as she called for local landowners to come together in a bid to stop the spread of Japanese knotweed in her area.

Richmond purchased her property, located in the town of Ashington in Northumberland, back in 2017 and undertook an extensive renovation project. Despite the revamp nearing its end, knotweed growing on land nearby now threatens the future of the house.

“It was quite a while after moving in that we found out about the knotweed,” she told Chronicle Live. “We thought it was being dealt with, but seeing it coming closer makes your heart sink.”

Local landowners, including Northumberland County Council, are said to be attempting to tackle the problem. Yet Richmond is urging for a long-term plan to eradicate Japanese knotweed from the area, where clusters have already been identified and treated.

What is Japanese knotweed?

Japanese knotweed (fallopia japonica) is a rapidly spreading plant, whose roots grow deep underground, suppressing other plant growth. A perennial, stem growth is renewed each year and by early summer its creeping bamboo-like canes begin shooting as much as seven feet.

Image: Its snowing in East Asia at en.wikipedia - Own work, Public DomainKnotweed takes over fast, and there are legal ramifications to ignoring it. 

If you get Japanese knotweed on your property it can be a real ordeal to get rid of. There is concern that Japanese knotweed can cause future damage to properties by growing under the foundations. It’s not proven whether or not this is the case, but what is definite is the way in which surveyors and mortgage lenders view the plant.

Will Japanese knotweed reduce my house's value?

Many mortgage companies will not lend to people if Japanese knotweed is located within seven metres of a property and likewise, most surveyors would advise against buying a property where knotweed is visible within the same parameters, meaning it can have a very detrimental impact on a house's value.

Crouch, Swale, CC BY-SA 4.0, via Wikimedia Commons
Japanese knotweed looks different in spring. Look for tell-tale red shoots like these.

Discussing their recent successful claim, Oonagh Burns, solicitor and director at Angelus Law, said: "Most peoples' most important and valuable asset is their home. 

"If Japanese knotweed is present on a property it devalues the property, due to the fact it is an invasive plant and by law a controlled waste, therefore it must be removed from your property, and costs thousands of pounds to remove.

"Further, Japanese knotweed can cause damage to structures such as paths and drains. We have settled many claims against property owners who have allowed Japanese knotweed to spread from their land onto our client’s land."

Japanese knotweed identification

Japanese knotweed has various stages of growth, meaning it can look very different (as you can see in these Japanese knotweed pictures), depending on the season.

It is usually seen from late spring to summer. According to the Royal Horticultural Society (RHS), in spring you may notice reddish-purple shoots at ground level that emerge from crimson pink buds.

By summer these will have grown into tall stands of bamboo-like canes that have purple flecks and branches from nodes along the plant’s length.

Japanese knotweed images

In winter, the stems die back to ground level (though the dry canes often remain for longer).

Other identifiable markers are creamy white flowers that hang in loose bunches in late summer/early autumn.

Japanese knotweed pictures

The shovel or heart-shaped leaves grow up to 14cm in length and create a zig-zag pattern along the stems.

Japanese knotweed identification

If you are a member of the RHS you can send photos of suspected Japanese knotweed for identification.

What do I do if there is Japanese knotweed on my property?

It is not illegal to have Japanese knotweed on your property but it is your responsibility to control it to prevent it from spreading to other properties. If you do not, you may be prosecuted and there are strict government guidelines that should be adhered to.

The law requires that a property owner declares the presence of any Japanese knotweed on their property when they come to sell.

If you are planning to buy a property where Japanese knotweed is present, the lender will normally require assurances that it will be removed before they transfer funds. This usually requires a management plan by a professional eradication company.

Japanese knotweed removal

Though small patches of the invasive plant may be managed by the homeowner, it’s not without its problems. As it is classed as controlled waste, any parts of the plant that you do manage to dig out must be disposed of at licensed landfill sites. Alternatively, you could wait for it to dry out and burn it.

It’s best to employ a specialised Japanese knotweed contractor and ensure that they are registered waste carriers before you employ their services. The Royal Institution of Chartered Surveyors (RICS) has set up a register of vetted consultants and contractors with the Property Care Association (PCA). Click on the map at the top of their webpage to find a local, accredited professional knotweed removal firm. 

Japanese knotweed treatment

Depending on how rooted your Japanese knotweed is, it may need to be treated with chemicals and you should expect to have to wait at least two seasons (three to four is more usual) to eradicate it using weed killer.

Though this can be attempted by home gardeners, it’s not recommended. Unless you use a professional company, you will not get an insurance-backed guarantee and you may run into problems when you come to sell your property or if a neighbour threatens to take legal action against you.

READ MORE: 13 common garden pests and how to treat them

Lead image: Dyfrain / Shutterstock


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