TEL: 01327 703129
(Head Office)

TEL : 01962 886060
(Southern Regional Office)


FAQs about Japanese Knotweed

Q. I want to sell my house and have Japanese knotweed growing in my garden. What should I do?


A.The attitude of mortgage providers to the presence of knotweed has been changing over the past few years. Previously, any hint of knotweed would see a mortgage refused but most lenders – particularly the big High Street banks – have now adopted a more measured approach. There are still some smaller lenders and quite a few mortgage advisors who will default to a refusal but if you shop around you should be able to find a less hostile response. As long as the knotweed is at a distance of 7m or more from your house, you should have no cause to worry. An appropriate herbicide programme will deal with this threat quite effectively. Even if the knotweed falls within the 7m zone, this should not preclude the sale of the property. Many mortgage companies are now quite happy to offer mortgages – as long as there is no existing damage to the property structure and as long as their ongoing requirements are met. These requirements will usually include a herbicide treatment programme with appropriate insurance–backed extended guarantees, to be provided by a suitable professional specialist. They may also require a Property Risk Survey.

Q.I have knotweed growing right next to my house. Is my house in imminent danger of collapse?


A.No. There are some sources in the media (and even within the knotweed industry itself, sadly) who would like you to believe this. In truth, knotweed rarely causes damage to houses unless they are already in a poor state of repair. Knotweed is a plant and, as such, requires light and moisture to thrive. It is unlikely to find this beneath a house, unless there is a clear pathway up to a source of light within the house. Therefore, even if the building foundations are shallow enough to enable knotweed rhizomes to grow beneath it, any exploration in this area by the rhizomes is likely to be limited and of insufficient strength to do any damage. Knotweed causes structural damage by exploiting weaknesses and so is more likely to affect drains, block paving, weak/thin/damaged cement, decaying/soft tarmac and single skinned walls, such as those found in outbuildings and on boundaries.

Where knotweed causes more catastrophic damage to buildings, it is usually the result of either neglect or incompetence. Japanese knotweed allowed to mature over several years (or decades) in an enclosed space (e.g. a gap between two walls) will produce dense crown material that will exert pressure on the surfaces confining it as it grows. Over time, this can lead to one of the surfaces cracking or collapsing entirely. It is not uncommon to find knotweed emerging through buildings that have been recently constructed on top of it. Responsibility for such damage can be laid firmly at the door of whoever constructed the building, since they evidently did not remediate the knotweed properly prior to construction.

Q.Can't I just treat the knotweed myself?


A.Treating Japanese knotweed is not rocket science. Provided there is proper understanding of the plant’s biology, as well as knowledge of how to choose and apply the correct herbicide effectively, the knotweed does not have to be treated by a professional. However, be advised, firstly, that even some so-called professionals can get this wrong and, secondly, that mortgage lenders do not recognise home treatment plans. They require fully documented programmes and appropriate guarantees. If these cannot be supplied, mortgage lenders may refuse a mortgage until a suitable specialist has become involved. Therefore, if you are planning to sell or re–mortgage your property in the foreseeable future, it may be best to contract a professional to provide treatment services right from the start.

Q.I have Japanese knotweed growing under a tree. Will your herbicides kill the tree?


A.The correct selection and application of herbicides to the Japanese knotweed will not normally kill or affect your tree. Be cautious! Some herbicides are capable of affecting trees, but our expertise will ensure risks are minimal. Our operatives are trained to avoid damaging any required plant and/or habitat.

Q.What if I have knotweed growing next door?


A.This is probably the most common knotweed problem. Property sales have fallen through over knotweed that was not the responsibility of the seller. Litigation, or pursuing action under The Anti-Social Behaviour, Crime and Policing Act 2014 are always options, but any such action should be seen as a last resort. It is always better to try and resolve the matter amicably with your neighbour if at all possible. Where knotweed is growing across boundaries and affecting more than one property it is always better, if feasible, to treat the knotweed as a single entity, regardless of ownership of the land it is growing on. This requires co–operation between all parties involved, though everyone will benefit from it if such co–operation can be achieved. If the knotweed is dealt with as a whole, all properties will be become more saleable as a result. If knotweed remains untreated on one property, then it will always present a risk of spreading back into treated properties in the future.

Q.Another company has said that they can kill my knotweed in 1–2 sprays. Why can't you offer this service?


A.These claims are frequently made by some of our competitors; claims that cannot be supported by either the Environment Agency or the pesticide manufacturers. In reality, overdosing the knotweed, or using chemicals with a strong residual element, often produces only short–term results. The knotweed is (in the vast majority of cases) put into a dormant state; that is, not actively growing for a time but then re–growing as the dormancy passes. Use of the wrong herbicide increases this risk and makes the spraying a waste of your money and likely to affect any plans you may have for the area in the future. The dormancy may persist for a season or longer (possibly several seasons), re–growing after this stage with as much vigour as before. Indeed, Japanese knotweed rhizomes have been found to lay dormant for up to 20 years (Environment Agency – Code of Practice) so the practice is truly not one to endorse. It is often quite possible to find viable rhizomes by disturbing the ground during the dormancy period and following this disturbance re–growth becomes more likely in the following season. In regard to use of residual herbicides, it is worth noting that the most commonly used residual product in the industry in the recent past was one called Tordon 22K, which contains an active ingredient called picloram. This product has been withdrawn from use in the UK, as of June 2015, meaning its use here is illegal – though it is still available to purchase online. This product was somewhat open to abuse, often being used in excess of the label recommendations. Through our own experience and testing procedures, we found this product to cause the greatest number of issues with dormancy for a number of years. Because of its ability to produce impressive short–term results, it was very popular and there may still be contractors using it despite doing so being in breach of the law. If you encounter a contractor using this product in the UK, please report them to the Chemical Safety Directorate (part of the Health and Safety Executive).

Q.How do I make a payment?


A.We bill you at each stage of an agreed programme as the works progress. For any new client we will request payment in advance for the first service we provide (e.g. survey visit, first treatment). Thereafter, we bill in arrears, providing clients keep within our credit terms. Customers may pay through their online Bank accounts (BACS), or cheque.

Q.What area does your company cover?


A.All mainland England and Wales is covered by our services, using a network of operatives based around the UK. Our operatives are home–based and so all operations are run through our Head Office in Northamptonshire and our Southern Office in Hampshire.

Q.What guarantees do you offer?


A.We offer two–year guarantees as standard and can offer extended guarantees (e.g. 10 years) where required. You will be advised of the conditions of any guarantee before work commences. These conditions will be stated on each of our quotations and may be subject to specified conditions. For instance, where untreated Japanese knotweed is growing on the other side of a boundary, reinfestation is almost inevitable, so we could not offer a guarantee in this circumstance. Guarantees are transferable to new owners.

Q.What about insurance backed guarantees?


A.‘Insurance backed guarantee‘ is an often used phrase in the industry that can be misleading. Insurance does not guarantee eradication and will not provide protection against structural damage. What Insurance will cover is an assurance that a PCA–approved contractor will be in attendance throughout the guarantee period (and treatment period, if covered by the Policy), even if, for whatever reason, our company has ceased trading prior to completion. All Insurance packages offered by The Knotweed Company are supplied by Guarantee Protection Insurance Ltd, who are authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority. Any Insurance product is granted entirely at the discretion of the Insurer and as such The Knotweed Company cannot guarantee your eligibility for these products. There are currently two Products available. The first is the Insurance Backed Guarantee (IBG), which covers the guarantee period only and as such only comes into effect once treatment has been completed. The IBG can cover up to ten years.

The second is the Treatment, Monitoring and Insurance Backed Guarantee (TM&IBG). This Product lasts 10 years in total but offers cover from day one. It applies to the treatment programme, the after–treatment monitoring and the guarantee period up to, but not exceeding, 10 years from the treatment commencement date. The TM&IBG must be paid for in full as a single lump sum payment at commencement of the programme. Please contact us for further information on these Policies. It is important to note that Insurance is an optional requirement and exists purely as a ’peace of mind‘ measure. That said, many mortgage companies insist on having them in place.

The Knotweed Company offers full site surveys, agreed herbicide programmes to control Japanese knotweed following all conditions of the Code of Practice and recommended herbicide practice. Control programmes may take 3 years or more to achieve completion. By following Best Practice, the customer and the mortgage company can be assured that completion will follow and their investment will be protected.

Whatever your knotweed problem in England or Wales, we'd be glad to hear from you. We offer the best solutions and most competitive quotes. Contact our Head Office on 01327 703129 or email us on

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