Japanese Knotweed Guide

All you need to know about Japanese knotweed

Do you suspect you may have Japanese knotweed in your garden? Or have you heard the phrase Japanese knotweed before and always wondered what it was? Here at Nimrod, we are experts in Japanese knotweed removal, we offer a range of removal methods and insurance-backed warranties and maintenance plans. So we have all your knotweed removal needs covered!

Within this post, we will cover topics from identifying Japanese knotweed in the UK, to the UK legislation involving Japanese knotweed, to best practices when it comes to removing knotweed.

What is Japanese knotweed? How and when does it grow?

Originating from the volcanic regions of Japan, Japanese knotweed (Fallopia japonica) is a giant weed which thrives on disturbance.  It uses this attribute to spread down watercourses, along transport routes and on to wasteland.

The plant itself is a perennial. Which basically means it will re-establish itself year after year.  It spreads via an extensive underground rhizome (root) system which can grow underground for up to 7 metres laterally and 3 metres in depth according to Environment Agency guidelines. It then uses this root system to grow up in other places.

In its native region Japanese knotweed is controlled by a range of natural pests and diseases including a weevil and rust fungus. Here in the UK, without these restrictions, it is thriving and its vigorous growth is a problem to our wildlife and capable of damaging buildings and hard surfaces. Once it is established in the built environment it can be particularly difficult to control.

Growing patterns

One of the things to note is that Japanese knotweed looks and acts very different, depending on what season we are in. Here is our guide to help you recognise Japanese knotweed in every season.


In spring, April to May, the weed grows extremely fast and it can look very different from one month to the next. Growing from small shoots (100-200mm) to anything up to 3 metres in height, the new shoots will be red/ purple in colour and look like asparagus spears. During its growth, leaves will sprout along the cane and start to unroll. In late spring when the canes are tall, they are hollow like a bamboo with purple speckles.


In summer, June to August, the weed will have reached its final height of approximately 2-3 metres and will stay at this height for the duration of the season. The plant will be a dense cluster of bamboo like stems with green leaves that have a distinct heart shape with a pointed tip. In late summer, August into autumn small white flowers will bloom.


Moving into autumn, September to November, Japanese knotweed will look similar to that in late summer, bamboo like tall stems, dense green foliage and small white flower blooms.  However, the leaves will begin to turn yellow and wilt.  The bamboo like stems will also turn darker brown.  During late autumn the canes will begin to die off and the plant becomes dormant.


During winter, December to February, the canes will begin to die off and lose their leaves as the plant becomes dormant.  The canes may remain standing or may fall over and can take up to 3 years to decompose.  Quite often, you will see canes from previous years at a different stage of decomposition and evidence of new shoots underneath the recent growth fall.

Japanese knotweed UK laws

The laws and legislation regarding Japanese knotweed differ depending on which part of the UK you are in. The Wildlife and Countryside Act 1981 refers to England, Wales and Northern Ireland whereas Scotland is covered under the Wildlife and Natural Environment (Scotland) Act 2011.

Although it is not against the law to have Japanese knotweed on your land, the law states that it is an offence to cause it to spread. Due to the destructive nature of the invasive weed, if Japanese knotweed spreads or encroaches onto your neighbour’s land you can face a conviction, a fine of up to £5,000 and / or six months in prison if you refuse to treat it.

In relation to the disposal of Japanese knotweed, legislation states that Japanese knotweed is classed as controlled waste and if not disposed of correctly may lead to prosecution under section 34 of the Environmental Protection Act (EPA) 1990. It must be taken to a licensed landfill site and if you are transporting Japanese knotweed waste you need a Waste Carrier’s license. Failure to show the license can result in a Fixed Penalty Notice of £300.

Japanese knotweed removal

Due to Japanese knotweed being ecologically harmful, it is strongly advised that if you think you’ve found Japanese knotweed on your land you should call us!  You can also email a photo to us at and we will email you back with the answer. No charge.

Nimrod treatment programs vary depending on whether we advise that spray treatment is the best course or another method such as excavation or soil sifting.

Depending on the size of the area, a spray treatment can take just minutes but the type of chemical we use will differ depending on the surrounding environment. Nimrod will then recommend a 1-year (included in the treatment price), 5-year or 10-year management plan to ensure eradication.

Using an excavation method, again depending on size of the area, can take up to several days. The management plan/ insurance backed warranty again will then ensure complete eradication.

What NOT to do if you find Japanese knotweed

  • DO NOT try to dig up Japanese knotweed as this will lead to a significant increase in stem density. Even a tiny fragment of the cut rhizome (root) is capable of regeneration.
  • DO NOT cut the stems without treating the roots. Cutting the stems encourages the roots to take on more nutrients that enhances the growth of the root system considerably.
  • DO NOT spread soil contaminated with Japanese knotweed rhizome. Any soil that is obtained from ground within 7m of a Japanese knotweed plant could contain rhizome. The rhizome is highly regenerative and will readily grow into new plants.
  • DO NOT remove it from the site unless taking it to an approved land fill site that will accept it and you have a valid Waste Carriers Licence.

Thank you for reading our article on Japanese Knotweed in the UK. Are you needing help with Japanese knotweed removal or Japanese knotweed identification? Don’t hesitate to contact one of our expert team members here.