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What is Japanese knotweed and what should you do if you find it on your property?

When buying or selling a property, Japanese knotweed is one of the most important things to look out for as this non-native plant can pose many environmental and structural risks. However, clearly identifying it isn’t always a straightforward task and often requires the help of a professional. It also spreads very easily, which means that there may be no clear signs of the plant when purchasing your property, but it may surface later. In this case, there are certain steps you can take to eliminate the plant before it can cause any damage to your property or spread further. 

If you’ve found Japanese knotweed on your property or it is present in a potential purchase, keep reading as we outline what you can do to get rid of it and how the sale may be impacted. We’ll also help you to understand what Japanese knotweed is and why it is a problem.

What is Japanese knotweed?

Japanese knotweed is an invasive plant species. It was initially introduced into the UK as an ornamental garden plant but it is now considered to be a weed. It is a strong clump-forming perennial that can grow very tall and spread easily, stunting the growth of other native plants. It dies in winter but is prevalent in the spring and summer seasons which is when it is usually spotted.

Why is Japanese knotweed a problem?

Japanese knotweed is a problem because it is incredibly strong and can exploit weaknesses in the structural integrity of the property and cause further damage to existing buildings. Not only can this pose a structural risk to your property, garden, or the surrounding boundaries, but the plant is extremely hard to eliminate. It requires specialist treatment, and this is a costly procedure. The growth pattern of the plant means that the rhizomes are problematic as they can grow to depths of two metres in the ground, and they can also extend up to seven metres horizontally, which makes it very easy for the plant to spread to neighbouring properties. The roots are very resilient and cannot be cleared with any regular weed killer, and even with specialist treatment, there is a risk that it can grow back.

UK laws surrounding Japanese knotweed

It should be noted that it is not illegal to have Japanese knotweed on your property, but it is illegal to allow it to spread to neighbouring areas. If you find it within your property boundaries, you are responsible for controlling it and making sure it is maintained in these boundaries. You are not permitted to dispose of Japanese knotweed as you would with regular weeds, as knotweed is considered ‘controlled waste’. 

If you allow Japanese knotweed to spread from your land into a neighbour’s property or into the wild, you could face a fine of up to £5,000. Because of the risks it poses and the controls in place,  when selling a property it is your responsibility to check for Japanese knotweed and make sure that any known presence is disclosed. Additionally, the police and authorities have the right to take action to control the spread of the plant if the home or landowner fails to do so.

How to get rid of Japanese knotweed

Japanese knotweed is notoriously hard to get rid of and it can take up to three to five years of specialist chemical treatment to eliminate it fully. If you find Japanese knotweed on your property, it is not recommended that you try to remove the plant yourself, as digging up the roots can cause it to spread further, and it can be carried on your shoes and clothes. It will also be able to regenerate from even the smallest remaining fragment, which is why it is such an issue. Instead, we would suggest getting a qualified specialist to create a treatment plan to remove and dispose of the plant correctly and avoid creating an even bigger problem.

What to do if you identify Japanese knotweed on your property

Japanese knotweed can be recognised by its large green, shovel-shaped leaves, white coloured flowers that bloom in clusters in the autumn months and thick bamboo-like stems with purple specks. It can be mistaken for other plants such as lilac and bindweed, so if you are unsure or are unable to identify the plant with confidence you’ll need to hire a professional. 

It is important that you do not try to remove it yourself as you’re likely to create a bigger problem due to the ease of spreading. The professional will be able to come up with a treatment plan for you. However, if you spot Japanese knotweed encroaching on your property from the natural environment or from a neighbouring property you can lodge a complaint with the local authorities. This is not a legal requirement, but it will help to prevent future issues and assist with controlling the spread of the plant. It should be noted that if the knotweed is encroaching from a neighbour’s property – you should only alert the authorities if you have already officially notified your neighbour.

How can having Japanese knotweed on your property affect sales?

Naturally, the presence of Japanese knotweed is likely to affect the value of a property as it poses structural risks as well as increased costs to remove it. Many lenders will not offer a mortgage on a property that is known to have knotweed, so this will rule out any potential buyers that aren’t paying for the property with cash. Disputes over identifying the plant may also result in delays in the buying process, and leaves developers or conveyancers who do not disclose any issues open to professional negligence if a property is bought which turns out to have Japanese knotweed.

As such, those who do find knotweed on their property and are looking to sell will typically choose to sell by auction. This is because experienced investors and developers, who frequently attend property auctions, are more likely to take on a ‘problem property’ having had prior knowledge of dealing with these sorts of issues. It is also worth noting that if a property on the street you are intending to purchase on has Japanese knotweed, this may put future buyers off purchasing due to the risk of the plant spreading. As such, if you are looking at making a purchase, you should try to research the nearby area to see if there have been any reports of the plant being present.

Get further advice on problem property sales with SDL Property Auctions

If you’re looking at buying or selling a property with Japanese knotweed and have further questions, we’d be happy to help offer further advice where possible, simply contact us and a member of our team will reach out to you shortly. However, you can also refer to the government website on dealing with Japanese knotweed for a more in depth look at the rules and regulations. We’ve also put together an advisory guide on selling a problem property by auction which includes more tips on streamlining your portfolio, so you can find reliable ways to sell even if you have Japanese knotweed, subsidence, or anything in between.