Everything you need to know about Japanese knotweed

What is Japanese Knotweed?

What Does Japanese Knotweed Look Like?

Japanese knotweed is a highly aggressive weed that can cause damage to property. With bamboo-like stems and small white flowers, knotweed can grow up to 10cm per day.

Throughout the year, knotweed looks different, and differentiating it from other plants can be tricky. Identifying knotweed does require a professional survey, and in winter, a dog detection survey helps to find dormant knotweed that isn’t flowering.

Japanese knotweed in spring:

  • The first signs of Japanese knotweed growth, Usually the early signs of growth are seen in mid-March
  • Distinctive red and purple shoots – often accompanied by rolled back leaves which grow rapidly from the stored nutrients in the rhizome.

Japanese knotweed in summer:

  • The stem resembles bamboo, though greener in colour with purple speckles.
  • Inside the cane are distinctive chambers that retain water and nutrients.
  • The leaves are large and have pointed tips that extend from the stem in a zig-zag pattern.
  • Later in the season creamy-white flowers hang in clusters from the stalks.

Japanese knotweed in autumn:

  • Bamboo stems turning a darker brown with a lot of foliage.
  • The leaves are large and have a heart shape with pointed tips that extends from the stem in a zig-zag pattern.
  • The leaves will be wilting and beginning to turn yellow.

Japanese knotweed in winter:

  • As the first frosts appear the plants leaves turn brown and the plant withdraws back into its rhizome.
  • The canes lose their colour and turn into woody stalks which can take years to decompose.
  • New shoots can be found growing through the dead canes in the early Spring.

How Did Japanese Knotweed Get Here?

Native to Japan, Korea and parts of East Asia and China, historical information shows us that Japanese knotweed was brought to the UK by a German-born

botanist, Philipp von Siebold in 1850. This was during a wave of popularity surging through Victorian Britain to collect and study plants from across the world. Japanese knotweed flowers and foliage were used for animal fodder and, at first, prized for their beauty—so much so, that in 1847, the species was named as ‘the most interesting new ornamental plant of the year,’ by the Society of Agriculture and Horticulture in Utrecht.

Inevitably, the interest in Japanese knotweed quickly evolved into, ‘How on earth can we get rid of it?’ because it proved to be a ferocious, invasive and destructive plant. In its natural habitat, on the side of volcanoes, the extreme climate, deposits of volcanic ash, native fungi and insects limited its spread, but in Britain, there are no such natural regulators or predators.

What Does Japanese Knotweed Do?

Japanese knotweed costs the UK economy an estimated £166 million per year for treatment and in property devaluations.

It spreads—rapidly—and it wipes out native species in its relentless progress across the land, as well as posing a serious threat to building foundations and drains. At its most prolific, Japanese knotweed can grow 20cm a day; its root system can go down to 3m; one plant can extend as much as 7m in every direction, and it can break through tarmac and concrete.

Japanese knotweed spreads like wildfire when it’s growing, but it also spreads when anyone tries to get rid of it, unless professionally managed by companies like Japanese Knotweed Specialists. The tiniest fragment of stem or rhizome will easily take root and regrow into another voracious plant, so it’s incredibly hard to eradicate completely if you don’t have the skills and equipment needed to carry out a thorough job.

For further information on the damage that knotweed can do, see:

What To Do If You Find Japanese Knotweed On Your Property

Call the experts and eradicate the plant before it spreads to avoid it entering neighbouring properties and land – it is your responsibility to stop it spreading.

Japanese knotweed thrives anywhere and everywhere, and so it will continue to thrive,

given half a chance, despite recent legislation strictly controlling the transportation and disposal of stems, roots and infected soil.

A smaller infestation can be stopped quicker than a large one. However, regardless of the size of the spread, knotweed must be eradicated, as the root system can spread quickly underground. It’s your responsibility to arrange for removal and treatment as a landowner, and to prevent the spread onto neighbouring land.

Our eradication methods are fully compliant with all current relevant regulations and carried out carefully to minimise risks to waterways, local environments and other plant species.

What Plants Are Mistaken For Japanese Knotweed?

There are a number of plants commonly mistaken for Japanese knotweed, including:

  • Bindweed
  • Himalayan Balsam
  • Bamboo
  • Broad-leaved Dock
  • Himalayan Knotweed
  • Himalayan Honeysuckle
  • Russian Vine
  • Lilac and Woody Shrubs

If you are unsure if your plant is knotweed or not, we offer a free, no-obligation service where you can email us at info@jkws.co.uk with your photos of a plant, and we will confirm whether it is knotweed or not.

What Is The Law And Legislation Around Japanese Knotweed?

Japanese knotweed is a highly regulated plant that requires extensive surveying and planning to eradicate. Japanese knotweed management plans are regulated and often required by local authorities.

There are currently multiple laws concerning Japanese knotweed, including:

  • EA (Environment Agency) Knotweed Code of Practice
  • PCA (Property Care Association) Code of Practice
  • Invasive Weed ASBO: The Anti-social Behaviour, Crime and Policing Act 2014
  • Wildlife and Countryside Act 1981
  • The Environment Protection Act 1990

Some laws are specific to certain areas, such as development sites or disposal, but others cover much wider areas such as the spread of knotweed to neighbouring land and the care needed to prevent that.

Japanese Knotweed and Property

Whether you’re buying, selling, or re-mortgaging, Japanese knotweed can have serious implications on these processes.

When buying a house that has knotweed, you’ll often need to get a management plan in place before you can agree on a mortgage. You may also need to have a survey done to show what invasive weeds, including Japanese knotweed, exist within the land, or neighbouring land.

Then with selling a house, you’ll have to have a TA6 form in place to show you have alerted the future house buyer about Japanese knotweed on the property. If you’re unsure, then a survey may need doing or you will have to tick ‘not known’ on the TA6 form.

Both selling and buying will need an expert PCA approved guarantee that lasts the length of a mortgage, like the one from Japanese Knotweed Specialists. You’ll also need a plan in place to ensure the sale and mortgage are accepted.

Contact us

With a number of different removal and treatment options available,
please call our specialist knotweed removal team on 0800 122 3326 for advice.