Japanese knotweed - The Facts

At the current time (summer 2012) the presence of even a small amount of Japanese knotweed perhaps several metres away from a property renders it a 'risk'. The weed is making it virtually impossible for properties to be mortgaged, leaving the industry and some homeowners in a state of panic.
Although Japanese knotweed does have to potential the to cause damage to buildings it is not a problem that can't be solved when handled correctly. It is understandable that the prospect of finding the weed on your property must be worrying; however once you can understand the ways to handle it, the plant immediately seems less intimidating.
At Prospect Materials we have had over 12 years experience and invested heavily in research and development to eradicate the species. With this record we would like to think we are able help to inform and reassure people that there are ways to overcome the issue of Japanese knotweed. With this in mind we have created a simple fact sheet using our expertise for those who encounter the species.
Japanese Knotweed     Japanese Knotweed
Common Misconceptions

'Japanese knotweed can grow through walls'
Japanese knotweed has the ability to work its way through gaps in between bricks and stone and not the brick itself. It is a tough plant and whilst it is true that it has the potential to damage buildings, typically it is usually only those of older construction such as random stone and soft lime mortar. The plant will exploit the weakness in any construction.
In over 10 years of eradicating Japanese knot weed infestations Prospect Materials have yet come across an incident of a modern house or even an older property (that has not been allowed to become derelict), damaged by the plant.
Japanese Knotweed     Japanese Knotweed
'Japanese knotweed can't be killed'
Although not the easiest species to eradicate, it is possible using various methods to remove the plant completely. The length of time it can take and the costs involved are what give people the impression it is an impossible task, along with the fact people can't kill the plant using off the shelf products. Prospect Materials have the expertise to offer removal in a single season and have developed methods to reduce costs and effectively kill the weed.

  • The species was introduced to the United Kingdom from Japan in the 18th century. Due to its commercial sale as an ornamental plant in the early 19th century it continued to spread throughout the country.
  • It is an offence under Section 14(2) of the Wildlife and Countryside Act 1981 to "plant or otherwise cause to grow in the wild" any plants listed in Schedule 9, Part II. Japanese knotweed is listed in this schedule
  • It is the responsibility of the owner of the property where the weed resides to prevent its spread into the wild or onto any neighbouring property. The owner of the property where it originates could be liable for its eradication.
  • It is illegal to dispose of Japanese knotweed as anything other than controlled waste.
  • In order to smother any other species present the shoots of Japanese knotweed can grow up to 8cm daily.
  • It can take as little as a 7g piece of the plant in the correct conditions for a whole new rhizome system to grow and spread into a full sized plant.
  • Japanese knotweed cannot produce fertile seeds and therefore not spread without the aid of humans, animals or watercourses.
  • The plant utilises underground rhizome systems both for food storage and to spread. Should the top of the plant be cut back there will still be an extensive underground system that will keep on feeding the plant and simply allow it to grow back.
  • Standard applications of herbicide or cutting the leaves back will not kill the route system and therefore can make it more difficult to eradicate in the long run.
  • In fact this can make matters much worse by putting the plant into a state of suspended animation from which it will eventually recover.
  • Effective methodologies have been developed over the last 10 years with proven success. Although it may take over a year to eradicate, once an appropriate strategy tailored for each infestation has been implemented the plant can no longer manufacture food from photosynthesis. The result of this is that its underground rhizome system is starved and therefore incapable of further significant growth.
  • A specially developed herbicide is best applied to full leaves so it can be well absorbed and fed down into the roots.
  • If the plant is to be dug out of the ground it is important that a sufficient radius excavated. The environment agency recommends that 7m x 3m deep is removed to ensure no remaining pieces can create new growth. Prospect Materials are able to reduce the need for this amount when using some of their methods of removal.
  • It is also imperative that the entire plant is removed and disposed of correctly. Fragments from shoes, clothing and tyres can easily spread the weed.
  • For guaranteed results it is imperative that the infestation is not disturbed during treatment and that the most suitable method of eradication is chosen by an expert.
  • It is estimated that the cost of removing the species from the UK entirely would be in the region of £4 billion
Although these facts can make removal of the weed seem daunting it is possible to control. Unless the infestation is within 7 metres of any building it is highly unlikely to cause any problems whatsoever to the construction or its foundations. There are a variety of solutions at varying costs and timescales that can be used to clear a property of the weed and by using an expert offering a guarantee, there is no reason why a mortgage should be refused due to a 'risk' that is minimal.
To summarise, the potential for damage to existing properties is grossly exaggerated. Certainly, if left to its own devices it has the potential, in common with many other plants, to cause serious structural damage. If there is no structural damage apparent at the time of inspection there is no cause for immediate concern, always providing that an appropriate control methodology is implemented.
Prospect Materials Limited
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