Everything You Need To Know About Japanese Knotweed
What is it?
Japanese knotweed is a fast-growing, invasive weed that originates from Japan. Unknowing Victorian botanists brought the weed over to the UK because they liked its aesthetic appeal, its similarity to bamboo and the fact that the stems could grow large enough to be used as fences. Over time, however, Japanese knotweed brought more disadvantages than benefits and its rapid spread has caused stress for homeowners, landowners and developers.
Not only can it cause massive damage, but the costs of removing Japanese knotweed, especially if the destructive weed has been left unchecked for years, can be substantial. That is why, at the first sight of knotweed on your property, you should act to ensure that the problem doesn’t grow out of hand.
The presence of knotweed on your land, or even in close proximity, can significantly affect your property value and impact on your ability to sell, or even make it difficult to secure a mortgage for a property that is known or suspected to be affected by knotweed.
Read on to find out more including the history of knotweed, identifying whether you have a knotweed problem, getting rid of knotweed, the dangers of knotweed and all the costs of knotweed, including the potential impact on property and mortgages.
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Japanese knotweed – a short history
Introduced to Britain by the Victorians in the mid-19th century as a quick-growing ornamental garden plant, Japanese knotweed (Fallopia japonica) was at first highly popular but very quickly grew out of favour, and has left a lasting legacy in terms of its invasiveness. The Victorians quite clearly didn’t realise what a legacy they were leaving behind!
Knotweed doesn’t cause the same problems in its natural environment in Japan, China and Taiwan because of the presence of natural predators such as insects and fungi which are not present in Europe. This means that the weed can grow virtually unchecked without human intervention.
Japanese knotweed can be found almost anywhere in the UK but is often found in abundance alongside railway lines. This is in part because Japanese knotweed was deliberately planted along the railway embankments to form stability. This can pose a threat to many properties adjacent to the railways.
There have been cases where property owners have successfully taken action against Network Rail where Japanese knotweed from a nearby railway line has then encroached on their property. Despite an appeal, the Court of Appeal ruled that landowners could claim damages if Japanese knotweed from the nearby railway line had impacted on their land. This has implications in setting a precedent for future cases where a landowner affected by the troublesome weed, which has originated from nearby railways, might be able to successfully bring legal action and claim for damages.
Although not illegal to have on your land, it is illegal to cause Japanese knotweed to grow in the wild, meaning that landowners who have the plant on their land have a responsibility to act. Classed as 'controlled waste' under the Environmental Protection Act 1990, knotweed, when removed from its site of origin, can only be disposed of at licensed landfill sites. Many local authorities have reported that fly-tipping of waste on road verges, lay-bys and waste ground have been a major factor in the spread of the dreaded knotweed.
How do you know if you have Japanese knotweed?
Japanese knotweed can be difficult for the untrained eye to identify as there are so many plants of varying species that it closely resembles. That is why identification should be carried out by experts who are used to the many different guises that the Japanese knotweed plant takes on through the year.
The growing season for Japanese knotweed starts typically in early Spring, and by the height of summer a plant could have reached several metres in height. It will continue growing until autumn before the surface growth dying off in the winter, although the growing season can sometimes extend if winter is mild or a summer is particularly warm and damp.
So, what does Japanese knotweed look like? Knotweed typically would be identified by its large green shovel-shaped leaves and bamboo-type stem. But the plant takes on different forms through the year with different coloured leaves and flowers present at various times depending on the seasons. It is not uncommon for a number of other plants, especially those with heart-shaped leaves to be commonly mistaken for Japanese knotweed.
Plants often mistaken for Japanese knotweed including bamboo, bindweed, bistorts, broadleaf dock, ground elder, Himalayan balsam, Himalayan Honeysuckle, Houttuynia, lesser knotweed and Russian vine.
Here are few identification tips about the leaves, flowers, stems and roots, to help you identify whether you might have Japanese knotweed present on your property:
Leaves on Japanese knotweed
Bright green, shovel-shaped with a pointed tip.
Leaves grow from the plant’s stems in an alternating zig-zag pattern.
Pronounced veins and mid-rib, and have a deep red or pink coloured stalk.
Leaves grow up to around 200mm across.
Early leaf growth for the first few days is deep red/purple or light green.
Leaves will die back in winter.
Flowers on Japanese knotweed
Small white or pale yellow clusters of flowers form in late summer/early autumn.
Flowers grow at the point where the leaf joins the stem.
Grows to approximately 100mm in length.
Stems on Japanese knotweed
Stems are hollow and bamboo-like.
New stems combined with fresh shoots take on the appearance of asparagus spears.
When mature in winter the stems become brittle and can be snapped easily.
Stems grow to 2-3 metres tall.
Roots on Japanese knotweed
Underground roots are known as rhizome.
Can snap easily like a carrot with the outside brown and inside light orange.
Can grow up to 3 metres deep and 7 metres across.
Grows underground to create ‘crowns’ year after year like the concentric rings on a tree.
Small fragments of rhizome the size of a fingernail can successfully grow into a new plant.
If you do think you’ve identified the plant on your property with help of ourJapanese knotweed identification tips above, then make sure you leave the plant where it is, especially the roots or rhizome, to avoid spreading the material to other areas where it might inadvertently take root and start growing all over again. Take pictures but do not remove any part of the plant until you have sought the advice of one of our experts who can advise you further.
Can you get rid of Japanese knotweed?
Japanese knotweed is extremely hardy and should really only be tackled and disposed of by an expert, especially if you want to be sure you have eradicated every last trace of it. DIY attempts to burn knotweed away or even treat it with bleach, as some people have tried, will be futile as it will continually keep growing back.
Current control methods rely mainly on chemicals. Herbicides, such as glyphosate based products, can be used in spray form on the foliage, but only in areas that are not ecologically sensitive.
Depending on the herbicide applied, late Summer/early Autumn is the most effective time to chemically spray Japanese knotweed as this is when the plant is in full leaf. By spraying onto the foliage just before the plant goes into senescence, will ensure that the herbicides effectively make their way to the root system.
In areas where spraying is not suitable and herbicides need to be used sparingly, stem injection methods can be used, whereby injecting the chemicals directly into the stem of the plants.
Herbicide treatments take time to work, with chemical treatments taking around 3 to 5 years to complete.
2) Knotweed excavation
The only way to be absolutely certain of permanently removing the Japanese knotweed is to professionally dig out the underground roots with machinery. The extensive network of rhizomes need to be carefully removed so as to ensure that no small fragments remain which could re-grow.
The excavated rhizome and soil would need to disposed of at a licenced landfill facility or an alternative plan for on-site burial (such as inside a heat-sealed geo fabric membrane).
3) MeshTech treatment of knotweed
In today’s more environmentally aware days, the use of herbicides is increasingly frowned upon as a solution to getting rid of Japanese knotweed. MeshTech provides a more eco-friendly alternative as it does not involve the use of any chemicals.
The new technique uses the knotweed’s aggressive nature against itself by forcing the plant to sever its own stems on a mesh placed over it where it grows. This method was designed by Dr Eric Connelly and JKSL, and has minimal impact on the surrounding environment, meaning it is an ideal deal technique for use on riverside locations, railway embankments and highways.
4) Biological control of knotweed
Another eco-friendly method includes the use of biological control in the form of releasing natural predators, such as the psyllids insect, which although it will not kill Japanese knotweed, may help naturally keep it under control.
Research has identified the psyllid, an insect naturally found in Japan, as safe for introduction to control Japanese knotweed in the UK. Several years of research in Japan and in quarantine facilities in the UK identified the insect as effective at controlling knotweed as well as the impact on native plants and invertebrates being low. The insects have been released around riverways where they were more likely to thrive and further research is continuing into the effectiveness.
How much does it cost to get rid of Japanese knotweed?
The rate at which Japanese knotweed can grow means that the longer you leave a known problem untackled then the greater the potential costs. Left unchecked, knotweed can cause thousands of pounds worth of damage to your property (and potentially surrounding property), and that’s before you take into account the costs of removing the knotweed itself.
So how much will it cost to remove Japanese knotweed? Much depends on the extent of the Japanese knotweed invasion, its location, and the best methods for its control and removal. Being able to grow up to 3 metres into the ground can make it extremely difficult to remove.
You also have to be sure that all traces of it have been removed to make sure that it does not grow back. That is why we recommend that you consult experts on removal rather than attempting a DIY knotweed removal.
As every Japanese knotweed case is different, it is difficult to put an exact measure on the cost of removal. Removal from a small domestic property would normally be considerably less than an extensive invasion on development land. The proximity to water and other environmental factors can make a difference in what treatments can be used and therefore the cost. Treatments can also involve a combination of methods.
A typical domestic residential property using a chemical treatment programme would cost in the region of £3,000 + VAT, while a small commercial site might cost £5,000 + VAT. Both would come with a 10-year insurance backed guarantee.
Any work requiring the use of mechanical methods, such as excavation and removal of infested soil and ground materials, can prove more expensive than chemical treatment methods. The cost will be dependent on factors such as topography, geology, access to the site, and potential ecological restraints. Costs typically start from around £7,000 + VAT. This includes a 15-year guarantee.
One factor which can impact on cost is whether the Japanese knotweed that is removed is able to be treated onsite or has to be disposed of off-site. As the plant is classified as controlled waste, it can only be disposed of at licensed landfill site, and transportation can only be done by a licensed carrier to ensure that the plant is properly contained and does not spread.
When all is considered the costs of Japanese knotweed removal may at first seem high, but compared to the potential damage that would be caused by doing nothing, then it really is a no-brainer. It also ensures that you would avoid any potential legal implications and costs should the knotweed have spread in future from your property to elsewhere.
How dangerous is Japanese knotweed?
Japanese knotweed is not dangerous in the sense that it is not poisonous to humans or animals, yet it’s impact on the environment can be huge. The knotweed grows at such a prodigious rate that it draws all the nutrients from the surrounding areas, causing all other competing plants with wither and die
However, it is the impact the plant can have on surrounding infrastructure that makes it a most feared weed for landowners and property owners. Above the surface the plant is capable of growing up to two metres in height, but it is what lies beneath that is of most concern. The roots of a Japanese knotweed plant can reach a depth of around 3 metres and can spread out over an area of more than 7 metres.
If left unchecked, the roots can cause significant structural damage to building foundations, walls, masonry and drains. At surface level the most obvious signs of knotweed damage will be where the plant starts to break through tarmac and paving stones.
At its worst, Japanese knotweed can cause significant subsidence to your property, especially if the property has weak points for the knotweed to exploit. The extensive roots can cause ground movements, affecting the foundations of a property.
It is the rate of growth which is of most concern, with the plant capable of growing almost 10cm per day, and likely to cause substantial damage in a relatively short space of time. If you suspect you have a problem with Japanese knotweed, then there really is no reason for delay.
What are the legal implications if I have Japanese knotweed on my property?
It is not illegal to have Japanese knotweed on your property, but it is against the law to cause or allow it to spread in the wild. This means that you could be prosecuted if you allow it to spread from your property.
If you discover knotweed on your land, you are not legally required to declare this, either to your neighbours of the local authority, though it would be illegal should you allow the plant to spread outside of your land.
If selling a property, you would be required to declare the presence of Japanese knotweed in a pre-contract questionnaire. A buyer could sue you should you fail to declare it when selling the property. Similarly, you could bring action against a seller who has not declared the presence of Japanese knotweed when selling a property to you.
What impact can Japanese knotweed have on my property value?
A knotweed infestation can have a significant impact on your property value, especially if the growth is substantial. There are numerous instances where a property value has fallen by tens of thousands of pounds due to the presence of the feared knotweed.
In one instance a property owner in Hertfordshire saw the value of his home, originally valued at £305,000 fall by £255,000, and he was advised the house would be unsellable until such time that the knotweed invasion was dealt with. That is of course and extreme case but there it is realistic to expect that a severe knotweed invasion would have a detrimental impact on your property value by many thousands.
According to the HM Land Registry price index, the presence of Japanese knotweed has reduced the value of affected UK houses by 10 per cent, leading to an average loss of £22,800 to property owners. It has been estimated that up to 900,000 UK households are affected by Japanese knotweed, meaning that almost £20bn has been wiped off house prices in the UK.
Can Japanese knotweed affect a mortgage?
The presence of Japanese knotweed has implications not only for landowners but also for borrowers who are seeking a mortgage. A potential buyer looking to secure a mortgage on a Japanese knotweed-affected property would usually be required by the lender to get a professional survey to evaluate any risk.
Much will depend on the proximity of the knotweed to the dwelling. It’s worth noting that the Japanese knotweed does not necessarily have to be on the property you are seeking a mortgage for. If there is knotweed on an adjoining property but within 7 metres of your potential purchase, then some lenders might consider this a risk and be less inclined to grant mortage approval.
Experience has shown us that most mortgage companies will lend on a property with Japanese knotweed, providing a professional Japanese knotweed company have been instructed to carry out the works and an insurance backed guarantee is in place.
What are the costs of knotweed to the UK as a whole?
Japanese knotweed is a costly business, both in environmental and monetary terms. Control and removal can impact on both domestic and commercial properties and can hold up planned developments, leading to costly delay.
Clearly, Japanese knotweed removal costs can be minimised by acting without delay once you suspect the presence of the plant on your land. If you think that Japanese knotweed is growing on your property then get in touch with us and we will be able to quickly confirm or dismiss this and advise on the next steps.
What to do next should you suspect you have Japanese knotweed?
JKSL have amassed over 15 years experience specialising in the prevention, control and removal of Japanese knotweed. Our team can ascertain whether you do indeed have Japanese knotweed on your property and can advise on your options.
As a highly trusted company, we utilise a range of highly effective techniques, including eco-friendly options, for dealing with Japanese knotweed issues. If you’re unsure whether you have Japanese knotweed on your land, then get in touch and we can handle it all for you. Depending on the type of work undertaken, our work is backed by 10 year guarantee so that you’ll have peace of mind that your Japanese knotweed issue has been permanently dealt with.
If you are not sure about identifying Japanese knotweed yourself, instead you can send us a picture of the plant you suspect might be Japanese knotweed and we’ll be able to quickly confirm or deny it for you. Alternatively get in touch and we’ll come around and give you a professional opinion.
I believe I have a Japanese knotweed infestation. How can I contact you?