Japanese knotweed: removal, identification and treatment

Updated on 12 July 2018 | 0 Comments

As a landmark case rules that Japanese knotweed is a real threat to properties, we outline what this invasive plant is and how you can treat it

Last week a judge ruled in favour of two homeowners whose properties have been invaded by Japanese knotweed that had spread from land owned by Network Rail, paving the way for others to sue their neighbours over the spread of the hazardous plant.

Stephen Williams and Robin Waistell, the owners of two adjoining bungalows in south Wales, successfully sued Network Rail last year over the spread of Japanese knotweed from land it owns. Network Rail challenged the decision at the Court of Appeal but on 3 July, the court ruled in Williams and Waistell’s favour and concluded that it was right that they were awarded substantial damages.

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 7ft.

If you get Japanese knotweed on your property it can be a real ordeal to get rid off. 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?

Most mortgage companies will not lend to people if Japanese knotweed is located within 7 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.

However, in announcing the court's decision, Master of the Rolls Sir Terence Etherton, said the ruling in the two plaintiffs' favour was down to the immediate burden it placed on the property owners as opposed to any perceived impact it may or may not have on the properties' values.

Etherton said: “Japanese knotweed, and its roots and rhizomes, does not merely carry the risk of future physical damage to buildings, structures and installations on the land. Its presence imposes an immediate burden on landowners who face an increased difficulty in their ability to develop, and in the cost of developing their land, should they wish to do so, because of the difficulties and expense of eradicating Japanese knotweed from affected land.

“In this way, Japanese knotweed can fairly be described as a natural hazard which affects landowners’ ability fully to use and enjoy their property and, in doing so, interferes with the land’s amenity value.”

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.

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.




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