Archive Website of the UK government

Why invasive plants and harmful weeds are a problem

Many non-native plant species exist in the UK without causing a problem, but a few become invasive. They upset the balance of the ecosystem, as they are bigger, faster-growing or more aggressive than the native species.

‘Controlling non-native wildlife’ has more detail on the harm invasive plants and animals can cause in the UK.

The Non-Native Species Secretariat (NNSS) website has information on what is meant by invasive, non-native species.

• Controlling non-native wildlife (environment and greener living section)

• What are invasive, non-native species? (NNSS) Opens new window

• Why invasive, non-native species are a threat (NNSS) Opens new window

Identifying common invasive plants

Four of the most invasive non-native plants are:

• Floating pennywort
  
• Japanese knotweed
  
• Giant hogweed
  
• Himalayan balsam

The Non-Native Species Secretariat (NNSS) has a database of invasive plants on its website. Most plants have a downloadable factsheet and an identification (ID) sheet linked to from the left side of the page.

Use the links under each section, below, to access the database.

Floating pennywort

Also called ‘water pennywort’ or just ‘pennywort’, floating pennywort is usually found floating on still or slow-moving fresh water. It can grow up to 20 centimetres a day, blocking out light and reducing the oxygen for other plants and animals.

• Floating pennywort: photos and information (NNSS) Opens new window

• Video about floating pennywort: NNSS Opens new window

Japanese knotweed

Japanese knotweed appears to have no natural enemies in Britain. It’s hard to control, as tiny fragments of its root can produce a living plant. It can grow as much as two centimetres per day, will grow in any type of soil, no matter how poor, and can grow through walls and concrete.

• Japanese knotweed: photos and information (NNSS) Opens new window

• Environment Agency advice on managing and disposing of Japanese Knotweed Opens new window

• Advice from the Devon Knotweed Forum on managing and disposing of Japanese Knotweed Opens new window

Giant hogweed

Giant hogweed can grow up to five metres tall and grows mainly in areas of damp soils, like river banks.

Giant hogweed can have adverse effects on skin following contact. Symptoms are usually noticeable within 24 hours, including blisters and swelling on the skin, which may be made worse by exposure to the sun. If you feel unwell after contact with giant hogweed, speak to your doctor.

• Giant hogweed: photos and information (NNSS) Opens new window

• The dangers of giant hogweed: NNSS Opens new window

Himalayan balsam

Himalayan balsam grows fast and can reach two to three metres in height. It rapidly spreads on the banks of slow-moving watercourses and becomes dominant, stopping other plants growing.

• Himalayan balsam: photos and information (NNSS) Opens new window

Identifying harmful weeds

Five particular plants are classified as 'injurious' (harmful) weeds under the Weeds Act 1959. These five plants are:

• common ragwort
  
• spear thistle
  
• creeping or field thistle
  
• curled dock
  
• broad-leaved dock

Ragwort is harmful to, and can kill, horses and livestock if eaten by them. All parts of the plant are poisonous.

The thistles and docks are economically harmful if allowed to spread, as they can stop pasture and crops growing properly.

The Department for Environment, Food and Rural Affairs (Defra) has a leaflet describing the five harmful weeds, including photos to help you identify them.

• Download 'Identification of injurious weeds' from Defra (PDF, 967K) Opens new window

• Help with PDF files

What you can do about invasive plants and harmful weeds

There are some general steps you can take to stop the spread of invasive plants. A list of these is given in ‘Controlling non-native wildlife’ under the section ‘How you can prevent the spread of non-native species’.

• Controlling non-native wildlife (environment and greener living section)

There are also some particular rules for certain invasive plants and all harmful weeds.

Invasive plants it’s illegal to place in the wild

Japanese knotweed and giant hogweed are listed in the Wildlife and Countryside Act 1981. This means it’s illegal to plant them in the wild.

Getting rid of harmful weeds

You can download guidance on controlling and disposing of ragwort and other harmful weeds from the Defra and Natural England websites.

Alternatively, contact the National Association of Agricultural Contractors for a list of approved contractors to control harmful weeds - or call them on 01733 362920.

• Download 'Guidance on disposing of ragwort' from Defra (PDF, 382K) Opens new window

• Help with PDF files

• Controlling the spread of harmful weeds and plants: Natural England Opens new window

• National Association of Agricultural Contractors Opens new window

Reporting harmful weeds

It isn’t an offence to have harmful weeds growing on your land. However, they mustn’t be allowed to spread to agricultural land, particularly land used for grazing horses and other livestock, or land used to produce animal feed. Natural England may issue enforcement notices to prevent the spread of harmful weeds to these types of land.

If you suspect harmful weeds are on land near you, you should try to contact the landowner to tell them the problem. If this doesn’t work, contact:

• Natural England, if the weeds are threatening land used for livestock or agriculture (you will need to fill in a complaint form)
  
• the Highways Agency for verges of large main roads (trunk roads) or motorways
  
• your local council for all other roadside grass verges or council owned land
  
• Network Rail for railway land or embankments

• Make a complaint about injurious weeds to Natural England Opens new window

• Contact the Highways Agency about weeds Opens new window

• Find your local council Opens new window

• Network Rail injurious weed information Opens new window

Non-native invasive animals

For information on preventing the spread of non-native invasive animals, like the American bullfrog, see ‘Controlling non-native wildlife’.

• Controlling non-native wildlife (environment and greener living section)

More useful links

• Weed control advice from the Royal Horticultural Society Opens new window

• Weeds Act 1959: Department for Environment, Food and Rural Affairs (Defra) Opens new window

• Ragwort Control Act 2003 Opens new window

• Identifying, controlling and disposing of invasive plants: Environment Agency Opens new window

Useful contacts

• Useful contacts