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It's Knot On. Japanese Knotweed. All Your Questions Answered.

Updated: Nov 26, 2020

I am sure many of you are aware of the property penetrating, nasty nuisance of a weed that is Japanese Knotweed. My partner and I have noticed it increasingly after viewing countless amounts of property in the past few weeks. So what is Japanese Knotweed and how can it affect your property structurally and financially?

What is Japanese Knotweed? Where did it come from, and how can we identify it?

Japanese Knotweed was introduced by the Victorian's as an oriental garden plant. It was harbored from Japan by the German botanist Phillipp von Siebold.

Japanese Knotweed has vibrant green leaves with a bamboo like stem and its flowers look like small creamy white clusters. It can be identified by a growth pattern of one stem per node, which forms a zig-zag stem growth pattern. When the plant is shooting in spring its reddish roots can look a bit like asparagus.

Japanese Knotweed was actually used in traditional medicine practice as a pain relief. However, nowadays it is more of a pain in the backside. Japanese Knotweed can grow up to 20cm a day and over four meters high, its expansive roots can sprout up to SEVEN meters below the soil. It causes extensive damage to brick work, drain systems, can grow through floors and small cavities and interfere with a property's structure. Knotweed costs the economy millions of pounds to treat every year and could increase a developers costs by 10%.

How does it spread?

Japanese Knotweed grows from the stem nodes in water or soil, the crown of the stem or the rhizome of the plant. Luckily it does not spread by germination, otherwise the seeds on the wind would be causing a lot of trouble! However, due to the persistent, and fast growing nature of the plant it can be incredibly difficult to eradicate.

How can you get rid of it?

Typically, it can be killed with a herbicide mixed with water, sprayed onto the leaves of the plant. Herbicides recommended include;








These are all glyphosate-based herbicides that will kill the plant. However, if any of the stem nodes, crown or even a tiny rhizome of the plant is left it can grow back even worse. This is why it is advisable to seek professional help when dealing with it on your property.

How can it affect your property?

Japanese Knotweed infiltrates any weaknesses in a property's foundations, walls, fences, ect. Spreading through moisture, the bamboo like rhizomes will force their way through brick work, floors and anything in its path. This can damage your property's structure and has been known to slash its value by as much as fifty-percent.

The Environment Agency describe Japanese knotweed as “indisputably the UK’s most aggressive, destructive and invasive plant”. It is estimated that 5% of UK property is affected by the plant.

It is important to establish whether or not the Knotweed is on your land, or in the vicinity of your neighbors. If it is in your vicinity then you could be at risk of a legal claim in “private nuisance” from your neighbor.

Many mortgage lenders will decline an application where the property is infected with Japanese Knotweed which is why many people choose to steer clear of it. However, some lenders are more flexible than others. A professional mortgage survey will be required to assess the risk the Knotweed poses to the property, based on their own policies they will determine suitability. There are generally four categories which lenders will assess the Knotweed which can be found on;

1. Japanese knotweed is not on the property but can be seen on a neighbouring property, which is more than 7 metres away from the boundary.

2.Japanese knotweed is seen on a neighbouring property, but is within 7 metres of the boundary.

3. Japanese knotweed is present in the boundaries of the property, but is still more than 7 metres from a habitable space (you may need to have further investigations completed by a qualified or experienced person).

4. Japanese knotweed is within 7 metres of the habitable space and/or causing serious damage to outbuildings, drains, paths and boundary walls. (With this fourth category, a further investigation would be required by an appropriately qualified and or experienced person.)

So it really depends on the severity of the situation in regards to getting a mortgage on a house with Knotweed.

The Property Care Association (PCA) have established Knotweed as 'another type of property problem that can be identified and treated with minimal impact.' However, they do also recommend that its eradication is a job left for the experts so it is extremely important to seek professional advice rather than deal with it yourself.

Who can get rid of Japanese Knotweed and how much does it cost?

There are many companies who specialise in the removal of Knotweed and the cost will depend on the area affected and the method of eradication. It is essential to ensure that the specialist you choose has the necessary certificates/training to get the job done. A mortgage lender will require a certificate to show that the Knotweed has been treated.

Below is a pricing table from, an environmental consultant company;

Of course prices differ from company to company but you get the jist. It can be a very costly process.

This is why most investors choose to avoid properties with Knotweed, unless the numbers still work extremely well after the cost of removal. A lot of the time, it's KNOT worth your time!

Thanks for reading!

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