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Cardiff Council

Weed Control


Cardiff Council has the responsibility to control all weeds found in the city's parks, housing estates and adopted highways.  

Currently the Council allows use of pesticides which contain glyphosate.  

Cardiff Council takes environmental issues very seriously and it remains the Council's objective to reduce the use of pesticides. As part of our Environmental Policy​​​​​​​​​​Link opens in a new window the Council is committed to undertake continual assessment of current and future practices to minimise the impact of actions on future generations and on the environment.   

Where we can, we will work to reduce the use of pesticides while still delivering a high quality, cost-effective and efficient service.   

This reduction is being achieved by:  

  • Working with our contractor to introduce specialist technology 
  • The use of adjuvants to reduce the amount of pesticide needed 
  • Evaluating alternative treatments and cultural practices to identify their potential within the constraints of legislation and available resources.   

The Contractor currently uses Monsanto Amenity Glyphosate, which carries no hazard warnings on its label, and is approved for use in the public realm by the Pesticides Safety Directorate which is an arm of the Health and Safety Executive. 

During 2022 our contractor used 3458 litres of this product to deliver the work programme.​

​What does Japanese Knotweed look like? ​ 

  • ​In March or early April, reddish-purple shoots appear.
  • The plant has distinctive heart-shaped leaves up to 12cm long.
  • By June, the clumps can be 2-3m tall.
  • Clusters of creamy flowers appear from August to October.
  • In winter the leaves and shoots die back leaving clumps of hollow stems.

Why is it a problem?​ 

Japanese Knotweed does not originate in the UK; it does not compete fairly with our native species and is able to spread unchecked. 

Although Japanese Knotweed is not toxic to humans, animals, or other plants, it offers a poor habitat for native insects, birds and mammals. 

This plant can cause damage to hard surface areas, and simple structures such as walls may also be affected if the plant is growing nearby. 

Legal obligations to remove Japanese Knotweed ​

There is no specific legislation which requires the eradication of Japanese Knotweed, but the following give some controls:  
  • The Wildlife and Countryside Act (1981) states it is an offence to plant or cause Japanese Knotweed to grow in the wild. 
  • The Environmental Protection Act (1990) states that cut Knotweed material and soil containing rhizome (root) material are classified as controlled waste and must be disposed of safely at a licensed landfill site if removed from the site of origin. It must not be placed in the green waste recycling or taken to landfill, except by a licensed waste contractor and with the knowledge of the licensed landfill site.   

Third party litigation Landowners can be sued for costs or damages if they fail to prevent Japanese Knotweed from spreading to a neighbouring property. Also, failure to manage and dispose of the plant responsibly may lead to prosecution. If you are affected by Knotweed from a neighbouring property, you need to take action before it gets near your buildings.  

How to dispose of Knotweed  

There are two methods which can be considered:   

- Excavation 

This is generally not a realistic solution for domestic gardens - it is a quick, but expensive way of dealing with the problem. The soil should be completely excavated to a depth of approximately 3 metres and disposed by an approved haulier using sealed transport to a landfill site that is licensed to handle this special waste.   

- Spraying with an approved herbicide  ​​​​

The most effective herbicides for use with Japanese Knotweed contain the active ingredient Glyphosate. This is found in a range of herbicides available to the domestic gardener. Glyphosate is effective on Japanese Knotweed even though it does not kill the plant immediately. The chemical is absorbed through the leaves and taken into the root system.  

This must be used in accordance with the manufacturer's recommendations, and it is important to realise that it will also kill any other plants growing in close proximity to the Knotweed if they are also sprayed. To maximise the effect of the chemical, it is best to spray in September and early October when the plant is still growing. This increases the volume of the pesticide absorbed by the plant, which takes it into the root system as growth slows down towards the winter.  

If there is too big an area for you to spray yourself, or you would prefer to use an expert company you should engage a contractor that is both PCA accredited and Amenity Assured.

Please note, even after treating the plant in this way for several years it is still possible for some of the root system to remain viable deep in the soil and for the plant to reappear within 5 years of the spraying work.  

If the plant is growing in more than one property you will need to ensure that all areas are treated to prevent re-infestation from neighbouring land.  

How to remove Japanese Knotweed from a garden ​

The stems and roots of this plant are classified as special waste, and this means that private residents cannot transport them to the Civic Amenity site or add them to the doorstep green waste collection.   

You can dispose of the waste by either letting the material dry and rot down on your own land or thoroughly burning the plant material on site (it is an offence to remove the material to other land under the Environmental protection Act, 1990).   

Whilst burning is an effective means of disposal, regard should be given to the size, location and timing of any fire, as smoke from premises can be a statutory nuisance under the Environmental Protection Act, 1990. Please contact the Pollution Control service on 02920 871650 for further advice on burning. 

What to do if you have Japanese Knotweed encroaching from neighbouring land ​​

You need to contact the landowner and ask them to take reasonable action to control the plant on their land, thus reducing the possibility of it spreading into your land. Start with friendly discussions, but if that goes nowhere, consult your buildings insurance company (some will act for you in such matters) or consult a solicitor. 


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