Every Japanese knotweed plant in the UK derives from one single plant that was brought here from Japan by Philip von Siebold in 1850. He was unaware of the environmental impact this plant would go on to have. The rest as they say – is history!
So here are the main reasons this plant is now a huge problem for residents and property management across the UK:
1. CostJapanese knotweed treatment and management costs the economy millions of pounds every year. A DEFRA analysis estimated an astonishing country-wide price tag of £1.5 billion for its control.
2. It’s growth pattern
The rhizomes can grow to depths of two meters and extend up to seven meters horizontally from the visible part of the plant. These roots are what allows knotweed to spread and are part of the reason that it is so resilient – they can remain capable of supporting life for up to 20 years.
It only takes a small amount of healthy root to give rise to an entirely new plant – and cause the infestation to re-emerge. When allowed to spread, or disturbed Japanese knotweed can grow under footpaths, and buildings, exploiting any weakness within the structure by growing through existing cracks or holes. Contrary to many statements you may read about knotweed – it does not cause actual ‘structural’ damage.
Knotweed can re-emerge and re-grow of its own accord any time, but especially if the contaminated ground is disturbed. This could be through digging or even common household gardening, also by extreme flooding which will carry fragments further afield where they will then establish and grow into new stands. A common myth is that planting knotweed in a pot will contain it – this is not the case.
3. Environmental ImpactIt’s rapid growth rate means it can smother other species, blocking sunlight with a dense canopy of leaves in summer. It also releases allelopathic chemicals into the soil that can stop other plants from growing. The large overwintering canes can block water channels increasing the likelihood of flooding.
4. Problems for developersAs disturbance to the rhizome will generate new growth, this is a real problem for developers. Ignoring knotweed can result in regrowth during or after construction, appearing through hard and soft landscape areas and even within the fabric of buildings themselves if there are any areas it can poke through.
If a developer or landowner does not undertake the necessary due diligence and control of Japanese knotweed, they risk legal action for professional negligence, which obviously has an impact on land marked for development. If knotweed is identified on a development site all works have to be stopped until a full survey and treatment or eradication has taken place. The location of knotweed must be recorded for future land sales.
5. Restrictions on amenity use
Knotweed can impede public spaces such as footpaths and sports fields, and if left untreated can spread into other amenity areas such as residential or public gardens, play areas or parks. This places severe restrictions of the free unimpeded use of the area.
6. Legal issues with buying and selling
Since 2013, when selling a property the seller is required to state whether Japanese knotweed is present on their property by ticking a box on the TA6 form – a property information form used for conveyancing. Failure to do so, or to make a false statement is deemed an illegal act that has consequences such as the seller being sued for ‘misrepresentation’.
If a professional survey is carried out and knotweed is either missed or mis-identified this is classed as ‘Professional negligence’
When developing a site affected by Japanese knotweed, if the necessary due diligence and control of Japanese knotweed has not been undertaken, the developers risk legal action for Professional Negligence. Ignoring knotweed can result in regrowth during or after construction, appearing on the property long after the site has been handed over to a Managing Agent – thus causing issues for the Agent and homeowners alike.
New legislation
An amendment to the Anti-social Behaviour, Crime and Policing Act 2014 includes invasive non-native plants including Japanese knotweed. RHS Guidelines state:
It is not illegal to have Japanese knotweed in your garden, but on your property you should aim to control this invasive non-native plant to prevent it becoming a problem in your neighbourhood. If it has a “detrimental effect of a persistent or continuing nature on the quality of life of those in the locality”, the legislation could be used to enforce its control and property owners may be prosecuted.
Where problems with Japanese knotweed occur in neighbouring gardens, we suggest that you speak or correspond directly with your neighbours (who may already be taking action to control this difficult weed). These informal steps should be taken before contacting your council to talk about action under the legislation.
Homeowners can consider control themselves for a small, isolated clump. However, a specialist professional company will be skilled at control, ensure eradication and can dispose of the plant waste at licenced landfill sites.
A Japanese Knotweed Management Plan is the answer
The Environment Agency states that once you find Japanese knotweed on private land or commercial development site, it is essential that you set up some form of Knotweed Management Plan (KMP).
It’s the survey findings that will go on to form a documented KMP for the property. This includes an assessment of the extent of the infestation, and severity of impact to the current or proposed future use of the property or land, which can include restrictions on maintenance and amenity use activities, and in rare cases damage caused to structures.
The presence of knotweed does not automatically prevent a mortgage from being obtained, with a case-by-case basis approach often adopted some mortgage lenders will agree. Evidence of a suitable KMP is paramount. Whilst it might be a shock to find out that the property you are trying to sell has knotweed, or indeed, the property you intend to buy is affected, there are treatments available to manage the infestation which will be clearly outlined in the KMP.
