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Japanese Knotweed: Frequently Asked Questions

Frequently asked questions


Japanese Knotweed Plus Ltd provides all listed services if Japanese Knotweed affects your property, e.g. if the Knotweed is present either within the property boundary or at reasonable distance from the property. Our standard procedure is as follows:

Free of charge identification of the Knotweed from the photographs sent to us by the client if possible.

Visiting the client’s site for detailed inspection if requested. 

Producing a formal Japanese Knotweed survey report with a management plan. Arranging a 10-year insurance backed guarantee if required.

Undertaking our treatment/monitoring course.

Issuing a  completion certificate that confirms that the treatment has been completed and that Japanese Knotweed at the property site has been eradicated.


Property vendor must report the presence of Japanese Knotweed if known. When completing the TA6 form the seller must answer the question in Section 7.8 “Is the property affected by Japanese Knotweed?” – Yes/No or Not Known. If the property is affected by Japanese Knotweed and a management plan on eradication provided by a reputable company is put in place there should not be a problem with selling the property. Usually, a conveyancer reports if any suspicious plants are present within the property boundary and/or around the property and suggests to do a survey by a company specialised in Japanese Knotweed. Reputable companies with PCA-qualified surveyors are able to identify Japanese Knotweed all year round and provide you with all paperwork required for smooth selling of the property.

It is a legal responsibility of the seller to report about Japanese Knotweed that affects their property. However if a seller, based on the best of their knowledge or with the intent to hide the Knotweed, declared “no” in the Section 7.8 of TA6 form, and it subsequently transpires that the plant is present, then the buyer may pursue the seller for compensation. First, the survey by a company specialised in Japanese Knotweed should be arranged. Qualified surveyors are usually able to determine if the Knotweed is well established and occupied the area for many years or was brought to the area in the last one-two years. The approximate age of the plant will be indicated in a survey report. If the plant was undoubtedly present in the area during purchasing the property a survey report will support legal actions against seller.

Property seller is legally obliged to report the presence of Japanese Knotweed if known. When completing the TA6 form the seller must answer the question in Section 7.8 “Is the property affected by Japanese Knotweed?” – Yes/No or Not Known. If Yes, please state whether there is a Japanese knotweed management plan in place and supply a copy. Normally, if a management plan to eradicate the Knotweed is put in place by reputable company and the work is covered by 10-year insurance backed guarantee provided by an independent insurer, there should not be a problem with getting mortgage. In most cases, the seller arranges treatment of the Knotweed that affects the property.

It is not illegal to have Japanese Knotweed on somebody’s land if it is well controlled by the owner and do not spread to the land of neighbours. However, once you decided to sell your property this may cause the problem and a potential buyer will not be granted mortgage unless the management plan on eradication of the Knotweed is put in place. In similar cases, we advise to our clients to discuss the issue with the neighbour to share the treatment cost. Unfortunately, in most cases, the neighbours will ignore to share the cost if they are not going to sell their property in the near future and you will need to pay for all treatment cost. It should be noted, that enforcing The Anti-Social Behaviour, Crime and Policing Act 2014 and Infrastructure Act 2015 against the neighbour having Japanese Knotweed on their land may be carefully considered and discussed with your solicitor.

Many of our clients find that the conveyancer has noted the plant on a neighbour’s land. Reality is that a management plan will need to be put in place to sell either your property or that of your neighbours. We would always advise that in the first instance you have a sensible discussion with your neighbour to see if they are happy to pay for treatment. If this fails try to  make a collective effort to pay for treatment.

We would advise seeking legal advice regarding responsibility for payment for treatment. unfortunately. It is still a grey area and the law is not clear.

It’s not illegal to have the plant on your land as long as it is kept under control and is outside the 7-metre zone from the habitable space (e. g. your house, garage or conservatory) and from the neighbouring property. However, once you decided to sell the property, the risk to the property will fall in to category 3 or 4 (depending on the distance from the habitable space) according to the RICS chart. It this case, the treatment will be formally required to sell the property.

The answer is Yes. After being warned, you would be considered as being a nuisance if you knowingly allowed the plant to spread to the land of your neighbours.

This action may be considered as spreading the plant. According  to the Wildlife and Countryside Act 1981, if any person plants or otherwise causes to grow in the wild any plant which is included in Part II of Schedule 9, such as Japanese Knotweed, the person may face a fine of £5,000 and/or 6 months imprisonment, or 2 years and/or an unlimited fine on indictment.

The Government should define and make the laws clearer regarding Japanese Knotweed. Potentially, in this case the neighbour is obstructing the sale of your property. We would suggest seeking legal advice. We can recommend a solicitor that will work for you under no win no fee arrangement if they think they have a good chance of winning your case for you.

In certain cases, the plant can weaken or even damage structures, such as brickwork, foundation, underground utilities, if left untreated. This is the main reason why the plant is under particular attention during selling/buying the property. From the other hand, due to the invasive nature of the plant, it quickly occupies new areas and pushes out our native plants, thus changing the ecology and food chain in the area.

Without special knowledge, it may not be straightforward to identify the plant correctly. The plant appearance changes throughout the growing season. Probably, the most difficult time for identification is winter, when only underground part of the plant including rhizomes/roots is alive and not visible.  It is worth mentioning that many conveyancers surveyors misidentify the plant or ask for a specialist report to prevent possible redress once the property has changed hands.

Our PCA-certificated surveyors can identify the plant all year round. In many cases, we can identify the Knotweed using photographs forwarded to us using email or our contact form in the bottom of the page.

There are several main ways in which the plant is spread:

(i) Animals such as foxes or badgers, are capable of bringing a small piece of the rhizome (underground stem of the plant that stores nutrients) on their fur into your garden resulting in regrowth.

(ii) Streams, waterways, railway lines.

(iii) Fly tipping, import of contaminated soil.

Rhizome fragments as small as 0.8 gram or stem fragments with two nodes are capable of regeneration into new plants.

It should be noted that the plant produces seeds in late summer. However, the seeds will not germinate as they are all female.

The bigger Japanese Knotweed companies will tend to recommend digging out the weed as this is the most expensive process.

However, we were advised that the Environment Agency recommends that wherever possible herbicide treatment is preferred method of treatment. Digging out and sifting soil contaminated with Japanese Knotweed will always carry a risk of regrowth on-site or spread to other sites through machinery and footwear. In contrast, applying chemical treatment minimises spread of the plant off-site. 

It is worth bearing in mind, while an excavation is being carried out on a large site, even the most secure sites will not stop foxes/badgers roaming through and looking for excavated worms or waste food left by the workmen. The animals may potentially pick up small fragments of the excavated rhizomes on their fur and transport them to unaffected areas.

Bunding the material on site for later herbicide treatment should be considered as an alternative option.

Obviously in some instances dig out can be the only option. Herbicide treatment normally takes 2-3 years followed by 2-year monitoring to eradicate the plant, whereas digging can be undertaken within short period of time. Time factor is indeed crucial for building companies. However, for most of the domestic and other customers who do not require works on site development, herbicide treatment is ideal cost-effective alternative.

We normally apply a two-year treatment course using herbicides to kill slowly the plant. The course will be followed by a two-year monitoring to ensure that the probability of regrowth in the future will be significantly low. The herbicide we use can be sprayed onto the leaves or injected into the stems. It will be drawn down into the plants vascular system and stop the production of amino acids which build up the protein that the plant needs to grow and survive. The plant will effectively slowly starve to death. If the plant is well established and densely populates the area a treatment course may be extended to three years.

Japanese Knotweed could turn to a dormant state for up 10 years if the wrong herbicide or wrong doze of herbicide is applied. We do tot recommend to use strong weed killers from your local DIY store due to the risk of dormancy. The use of other substances such as diesel petrol, vinegar, white spirits, etc. must be avoided due to the risk of contamination of soil, while they will not kill the Knotweed.

It is always advised to refer to specialist companies that are qualified to use professional herbicides and are have license to handle and apply them. Note, that operation under ‘Grandfather Rules’ exemption’ is no longer allowed since 26th November 2015. If you were born before 31 December 1964 you are not allowed to apply professional pesticides on your land unless you hold a recognised certificate. 

Be aware that mortgage lenders will not lend money on property with Japanese Knotweed history that was treated or under treatment with no proper paperwork produced by specialist company, i.e. management plan.


Indeed, weed membranes to create a control barrier against Japanese Knotweed are available in the market, for instance Dupont Plantex Platinium. You can cover the infested areas on your land to prevent plant to appear on that particular area. However, the membrane will not kill the plant and it may eventually spread behind the covered area if other measures are not undertaken. Further, it is now legal requirement to report Japanese Knotweed if you sell your property. Most likely, mortgage lenders will not be satisfied if membrane is deployed as it will not kill the plant. Further, if Japanese Knotweed was intentionally hidden during selling the property and it later reappears, you may be liable for compensation, e.g. excavation/herbicide treatment cost.

The only general rule is to prevent spread the plant or soil contaminated with the plant fragments outside of your property boundary.

You can compost or burn (if allowed) it on your land.

You must not put the plant/contaminated soil in the bin for general/garden waste.

You can arrange disposal of the Knotweed off-site. However, as it is classed as a controlled waste, the transport must be undertaken by dedicated waste carrier to licensed landfill site and accompanied by the appropriate waste transfer documentation.

The treatment is normally applied when the plant is at least three feet high. It should have sufficient foliage area to adsorb enough herbicide to be translocated to the rhizome system if applied by spraying. If injection is preferable, the stem thickness should be 1 cm or over. Normally, first treatment may be applied in the end of June to beginning of July, with the second treatment in September, or up to beginning of October in mild weather conditions.

Treatment by spraying can not be applied in wet weather conditions. The plant can be sprayed at least two hours after rain stopped and at least half an hour before the rain is expected.

Injection of herbicide can potentially be carried out in any weather condition. However, after prolonged raining, bottom of the stems used for injection may be filled with water that may reduce treatment efficiency. Thus, a couple of days after prolonged raining should be allowed for efficient treatment by injection.

The plant is not harmful to you or your pets, in some cultures the plant is actually used for medicinal purposes. Further, various Knotweed recipes, including Japanese Knotweed wine, are available online. Remember, if cooking Japanese Knotweed in your house. The plant fragments may be taken from your land only. Otherwise, it may be considered as an attempt to spread the plant, with possible legal consequences.

Surprisingly, in some areas of Scotland the plant is actually protected as it shelters otters while they are migrating between different wet areas.

According to the documentation of the manufacturer of the herbicide we use it is not classified as dangerous.

Not expected to produce significant adverse effects for the environments when recommended use instructions are followed.

Not a persistent, bioaccumulative or toxic nor a very persistent, very bioaccumulative mixture.

At short term eye contact, skin contact, inhalation: not expected to produce significant adverse effects when recommended use instructions are followed.

It is not harmful for pets. However, it is recommended to keep pets out during the treatment until herbicide has dried up as they could bring wet herbicide to the plants that should not be treated.

If we spray herbicide close to your house, we always ask to shut doors and windows and keep pets out to avoid any unknown issues that may be caused by treatment.



Any more questions?

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