The invasive perennial plant Japanese knotweed is the most damaging knotweed in the UK, having spread to every part of the country. Japanese Knotweed continues to expand across the UK via rhizome fragments and is proving harder and harder to remove.
Our map shows the high-risk areas of Japanese knotweed in the UK and where the highest infestation areas are for homeowners.
Japanese knotweed is an invasive weed that can cause serious problems for homeowners. It has been found in many areas of the UK and it’s important to know how to identify if you’re at risk of infestation.
In the United Kingdom, there is presently one Japanese knotweed infestation for every ten square kilometres. Check out the coloured map below to see how badly the remainder of the UK has been affected – the darker the shade of the region, the more Japanese knotweed has been identified.
Our Japanese Knotweed distribution map includes known hotspots of this weed’s infestation.
What is Japanese knotweed?
Japanese knotweed is a plant that can decrease a home’s value and cause disputes between neighbours. The invasive plant has a reputation for growing swiftly and taking over gardens. Japanese Knotweed may cause serious damage to foundations, flood defences, and walls, among other things.
Knotweed spreads in enormous swaths, quickly displacing any other plant life in its path. Thankfully, Japanese knotweed is easy to spot, so homeowners can get started on a treatment plan right once.
Where is Japanese Knotweed from?
Japanese knotweed is native to Japan, but it is also found in China and Korea. The plant is one of a number of species that have been discovered growing on volcanoes’ sides. Japanese knotweed may reproduce spontaneously in its native region and benefit from a large underground rhizome system.
Knotweed is kept in control in its natural environment by natural predators such as fungi and insects, as well as other plants and an environment that can be far more hostile than the United Kingdom.
How to recognise Japanese Knotweed in the UK
Often confused with many other common weeds, Japanese Knotweed is frequently wrongly identified throughout the UK.
For a thorough, in-depth look at how to identify Japanese Knotweed, including many Japanese Knotweed pictures, check out our complete guide to Japanese Knotweed identification. Here’s a detailed list of the tell-tale signs for UK Japanese Knotweed.
- Japanese Knotweed red shoots emerge around Spring
- In late spring, Japanese Knotweed canes can reach up to 3 metres (10 feet) in height
- Shovel/Heart-shaped 20cm long leaves unravel early Summer
- Knotweed’s hollow bamboo-like canes begin to turn brown in late summer
- Japanese Knotweed flowers form in small cream-white clusters from September
- Throughout the year, Japanese Knotweed Rhizomes can be identified by their dark brown exterior and yellow/orange interior
- Starting in late Spring, Knotweed leaves grow in a zig-zag staggered pattern on the plants’ stem
- During Winter, UK Japanese Knotweed appears to die back as its leaves turn brown and drop off
- Throughout the UK winter, Japanese Knotweed stems turn completely brown while the plant’s rhizome network is still thriving below the surface
Where is Japanese knotweed found in the UK?
Japanese knotweed has been found all throughout the United Kingdom. Knotweed is still wreaking havoc in the north of England and the Midlands, according to new UK heat map data. The highest concentration of Knotweed in the United Kingdom is in the North West of England.
According to the Royal Horticultural Society, Japanese knotweed is found in approximately 30% of the worst-affected areas within the UK. However, this figure may be higher due to a lack of identification or reporting.
It is estimated that the UK spends over £166m a year on the control and management of Japanese knotweed.
The worst-affected area in Bolton, Lancashire, UK, has 652 infestations within a 4-kilometre radius. Numerous other Japanese knotweed hot spots may be found in Bristol, Rotherham, Nottingham, and Glasgow. London, England, also suffers from significant concentrations of knotweed, with over 200 occurrences within 4km in many locations.
The majority of Japanese knotweed in the United Kingdom is found in northwest, southwest Wales, and central London.
How did Japanese knotweed spread throughout the UK?
The Japanese knotweed’s robust, almost woody stalks grew up to 20cm each day, at an unheard-of rate. This hardworking machinery proved to be particularly valuable during a period of strong industrialisation and development. Hundreds of these plants soon lined the gardens, bolstering banks along potential railway lines, and being eagerly shared among gardeners.
Despite the worrisome rate of growth of this new discovery, Victorians thought they had it under control. The fact that only one gender of the plant was brought gave them confidence. Gardeners and scientists congratulated themselves on their resourcefulness in obtaining control of such a useful creature, but they hadn’t considered the potential that this alien plant may reproduce itself in another way.
Known as ‘the largest female in Britain’ by some horticulturists, every single Japanese knotweed plant is a clone of the original female plant that was introduced to Britain over a century ago. On a cellular level, the plant’s outstanding dispersion across the country can be attributed to its architecture. Rhizomes are fragments of the plant’s roots that can travel far from their source and grow into completely new plants on their own.
Is there Japanese knotweed in my area?
The UK government has since identified Japanese knotweed as an invasive species, making its unlawful removal or transportation a criminal offence. This hasn’t stopped it from spreading farther across the UK, with only communities in the country’s northernmost regions untouched.
Knotweed generally remains dormant in root systems beneath the ground throughout the colder months, making it difficult to determine how far the plant has spread. The government spent an estimated £70 million on an infestation detected in the run-up to the London 2012 Olympics, while Swansea has been besieged for decades, with the local council battling an ever-expanding 250 acres of knotweed.
Where does Japanese knotweed grow in the UK?
Japanese knotweed is now found in practically every part of the United Kingdom. Knotweed is primarily found in the suburbs of major UK cities such as London, Manchester, Liverpool, Birmingham, and Newcastle, as seen on the Japanese Knotweed UK map above. Japanese Knotweed is also common in England, particularly in the South East, where it can be found in places like Cornwall.
Before the government recognised Japanese Knotweed as an invasive species, it had spread across the country for almost a century. Japanese knotweed had already been disseminated by gardeners, dug up and moved by urban building projects, and even employed to stabilise soil on the sides of railway lines by the time it was identified as an invasive hazard in 1981.
The plant can be found growing alongside public waterways like canals, as well as railway lines, highways, and public footpaths. Japanese knotweed thrives in a wide range of environments in the UK and is frequently found growing on abandoned or unmanaged land. As a result, significant infestations are frequently found in overgrown backyards, gardens or abandoned industrial sites.
How common is Japanese knotweed in the UK?
In the United Kingdom, Japanese knotweed is fairly common. Since the government declared Japanese knotweed a national emergency, efforts have been made to track its growth across the country.
It has been feasible to identify the areas of the country that have been most affected by Japanese knotweed using this information. The most impacted areas in the UK are Bolton, Bristol, Conwy, Rotherham, and Nottingham, though exact numbers are difficult to estimate.
What do I do if I find Japanese knotweed?
If you detect Japanese knotweed, it’s critical to figure out where it came from and how much it’s affecting your land. Before approaching any neighbours who could have the plant on their property, you might wish to consult with a Japanese knotweed expert to ensure a positive diagnosis.
Ignoring the infestation is not a good idea because the plant can quickly multiply, creating a bigger difficulty to deal with and maybe more costs if you can’t get recompense for the treatment costs.
If you think you’ve discovered Japanese knotweed and need help figuring out what to do next, please contact us. We can assist you in identifying your Japanese knotweed problem and hiring a professional team to eradicate it.
With Japanese knotweed being so aggressive as it spreads across the UK and more importantly on your property then it pays to call the experts who can eradicate this problem and provide the necessary guarantees that banks and building societies look for.
Want to know more about Japanese knotweed in the UK?
Knotweed Removal aims to provide the most up-to-date information, help and advice for YOU to make informed decisions. If you are unsure or uncertain about how to proceed, please reach out to us and we will gladly come back and advise you as best we can.
The best means to contact us is via our email – email@example.com
Do not forget we have a library of blogs covering many areas relevant to Japanese Knotweed, our free downloadable How-to Guides and Product Reviews on the latest methods being employed to eradicate or remove Japanese Knotweed.
Knotweed Removal, UK