FAQs

The following FAQs are addressed below:

Why can't I get rid of knotweed by simply pulling it up, cutting it regularly or covering it with a tarpaulin?

Hand pulling knotweed stems will merely encourage the knotweed to produce new stems to replace them. Pulling will also almost certainly result in fragments of crown material being pulled out of the ground with the stem. Once stems (or stems and crowns) have been pulled, there is the issue of disposal. The stems can be dried out and burnt when they are dead, but crowns can survive drying out and partial burning. If stems/crowns are disposed of off-site, they need to go to landfill, as sending them to the local amenity tip or fly tipping them is a prosecutable offence. Hand pulling is suitable, however, for very small, immature infestations, where the stem will come easily out of the ground with most or all of the rhizome intact. On such growth, crowns will not yet have started to develop and stems can be dried out and burnt.

Some say that regular cutting or mowing of knotweed stems will weaken the rhizome sufficiently to prevent new growth. There is some truth in this, but it will take several years of cutting or mowing before the plant is weakened to the point of producing no new stems and there is also the issue of what to do with the cut/mown material in the meantime. Also, there is the danger that the remaining rhizome could simply slip into dormancy for a year or two and spring back with renewed vigour.

Spreading tarpaulins, carpets or membranes over knotweed is a popular method expounded by allotment owners. The theory is that the plant, starved of light, dies within a year or two. While this is an effective method for many plant species, knotweed is not killed off in this manner:

  • Unless the membrane is strong enough, the knotweed will merely grow straight through it, ripping it apart.
  • If the membrane is thick enough to inhibit knotweed growth, the plant is more likely to go into dormancy - effectively extending the process it goes through every winter. Current estimates for how long knotweed can remain dormant are around 20 years, which is a long time to leave down a temporary membrane.
  • If the membrane is removed while the knotweed is still alive it will simply grow back.

How do I make sure I buy land without knotweed on it?

This question is being asked more often by clients, meaning surveyors are under increasing pressure to ensure they do not miss any evidence of Japanese knotweed growing on land/property that is being purchased. There are plenty of unscrupulous landowners out there who will do everything they can to disguise their knotweed problem to ensure they do not end up having to accept less money for their property.

  • Be suspicious if land looks freshly scraped. Find out why it has been scraped.
  • Look for signs of knotweed debris on the surface.
  • Look for evidence of knotweed stems that have been cut down recently - the base of the stems and, if the stands are mature, the tops of some crowns will probably still be visible.
  • Knotweed is notoriously difficult to see during the winter. A large stand of dead canes can be pretty easy to spot, but less mature stems are virtually impossible.

However, do not be put off from buying land/property with knotweed on it. Providing that a long-term approach can be taken, knotweed can be treated effectively and relatively inexpensively. Get quotes for treating the knotweed and use these as bargaining counters to reduce the cost of the sale.

How will knotweed affect the value of my property?

Knotweed can damage structures, spread into adjoining properties, dominate other forms of vegetation and cause delays to any development projects, so most buyers will not want it there. Knotweed costs money to treat and buyers will be looking to be recompensed for this expense out of the purchase price. In short, the more knotweed is flourishing on a piece of land the less value that land will have to a purchaser. So implementing some form of treatment programme and bringing the knotweed under control before deciding to sell will be of great benefit to any seller.

When it comes to selling residential and commercial property, the presence of Japanese knotweed can have a significant impact on your ability to sell. In recent years mortgage lenders have become hyper-sensitive over the issue of knotweed. Many have refused to lend when knotweed is present - even in cases where it is present on adjacent land but not within the boundaries of the property in question.

RICS have worked with the Council of Mortgage Lenders (CML) to help establish guidelines for use by surveyors. In addition, the Property Care Association (PCA) have drawn up their own code of practice on the treatment of Japanese knotweed. Despite the existence of such guidance, many lenders continue to adopt an extreme stance when it comes to the presence of the plant, mainly because they are scared their investment will lose its value and become uninhabitable in a few years if the spread of the knotweed in the vicinity of the property is not checked.

At the time of writing (2013) Barclays, through its mortgage arm Woolwich, have adopted the position that they will automatically refuse funding on any site containing knotweed even if it is subject to treatment. Lenders such as Precise Mortgages, Halifax, Saffron Building Society, Coventry Building Society, Santander, Skipton Building Society, Nationwide and Nat West have demonstrated a little more flexibility, though they all have their own stipulations that would determine when they would lend. Some are prepared to lend once the knotweed has been dealt with by an approved company, others would consider lending if an insurance-backed treatment programme was already underway. If your lender refuses to mortgage then it may be worth shopping around. However, it is clear that Japanese knotweed anywhere in the area could have a detrimental effect on the ability to either buy or sell buildings or land.

Indeed, even with the more flexible of the lenders, if knotweed has been left unchecked for many years and has completely taken over a particular site, then sale of this property/land may prove impossible.

Is Japanese knotweed dangerous to touch?

Unlike Giant hogweed, Japanese knotweed is not harmful to touch. In fact, the plant is edible and rich in Vitamin C. With a taste reminiscent of rhubarb there are lots of recipes available on the internet for anything from stir-fries to soup, crumbles, ice cream and wine. Be aware, though, that not all of the plant is suitable for consumption and the optimum time of the year to pick it is the spring when the plant is still soft. Japanese knotweed has health benefits, too, as it can act as a mild laxative. The rhizomes contain an anti-bacterial and anti-fungal substance called resveratrol, which has proved beneficial in the treatment of such complaints as athlete's foot, dermatitis, gonorrhoea and herpes. Laboratory tests in Japan have seen resveratrol taken from knotweed reduce tumours in mice by over 40%.

A word of caution, though, if you are planning to eat any knotweed in the UK: make sure the knotweed has not previously been treated with herbicides and bear in mind issues of disturbance, disposal and spread. Make sure you don't end up breaking the law!

What can I do if knotweed is spreading onto my land from adjoining land?

The best thing to do in this situation is to talk to the owner of the neighbouring land. Try and discuss the matter with them and make them aware of what knotweed is and why it should be controlled. If both parties can mutually agree a way forward, probably involving treating the plant on both sides of the boundary and, as appropriate, splitting the costs, this will save considerable expense and stress.

If entering into such a dialogue is impossible, for whatever reason, then current legislation offers little support. Local authorities will not get involved as a rule with private disputes and neither will the Environment Agency or DEFRA. Knotweed is the responsibility of the person who owns or occupies the land it is growing on so these government bodies only show any interest if they actually own some of the land in question.

If polite bargaining, supplying of information or even a solicitor's letter leave your neighbour unmoved then the only course left open may be to pursue third party litigation, which can prove expensive and has no guarantee of a successful outcome.

The Environmental Protection Act 1990 does allow for the Environmental Department of local authorities to serve orders against those responsible for providing a private nuisance to their neighbours - defined as 'unlawful interference with a person's use or enjoyment of land, or some right over, or in connection with it'. While this is most commonly cited in relation to noise, there is an argument for suggesting that a Japanese knotweed infestation spreading onto your land and possibly damaging walls, paving, etc. can be deemed to have interfered with your enjoyment of your land. However, this will need to be proved in a court of law and to pursue it you will need a solicitor who is dedicated to making the case (and funds to pay for their services). DEFRA has tried to assist the situation by suggesting local authorities enforce lack of control of knotweed growth by invoking the Town and County Planning Act 1990, arguing that knotweed can be deemed to 'adversely affect' the amenity of the neighbourhood. However, this has been greeted with differing levels of interest by councils across the UK.

What should I do if I am developing land with knotweed on it?

If the land is to be developed, draw up a knotweed management plan (KMP) before any works commence and stick to it throughout the project. Information on creating a KMP, as well as the importance of doing so, can be found in the Environment Agency's Knotweed Code of Practice. Unless you are well versed in knotweed issues and methods of treatment, consult a knotweed expert when drawing up the KMP.

Why can't I just put knotweed in standard green waste?

The Environmental Protection Act 1990 and Environmental Protection (Duty of Care) Regulations 1991 cover the disposal of all knotweed regardless of site of origin. Private house owners can be just as culpable as building developers when it comes to removing knotweed material from their properties.

Knotweed can regenerate from small fragments of itself so merely cutting it down or digging it up will not necessarily kill it. Putting cut stems onto a compost heap in your garden, for instance, can lead to knotweed growing within the compost heap - making the compost unusable. Green waste taken to civic amenity tips is composted and recycled. In this situation, knotweed will be allowed to spread to other sites where it will regrow - this is in breach of the law.

Will the Japanese knotweed bug completely remove the knotweed problem?

The so-called 'knotweed bug' is a psyllid called Aphalara itadori. In its native lands it is a natural predator of Japanese knotweed and has been selected after years of research by the not-for-profit organisation CABI as being suitable for release in the UK. Research began on finding a suitable biological predator in 2003, following a series of fact-finding missions that started in 2000. Care was taken to ensure that whichever biological control agent was selected would not have a detrimental impact on any species other than knotweed. In 2010, the government approved the limited release of Aphalara itadori to ensure its suitability for later national release. It has been released on a small number of specially selected sites across England and Wales and its impact on those sites will be closely monitored over a period of 5 years.

The psyllid lays its eggs on Japanese knotweed and the young then feed on the sap as they grow. This activity will introduce an element of natural control to the knotweed problem, since it will reduce the plant's ability to grow and spread, but it will not eradicate Japanese knotweed from the UK. In addition, it will take between 5-10 years following national release for the effects on the knotweed population to become apparent. The 'knotweed bug' is an important long-term measure for controlling the spread of knotweed but will not remove the problem from the UK.