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Invasive non-native plants

Japanese knotweed © Laurie Campbell

Invasive non-native species are considered to pose one of the greatest threats not just to the biodiversity but also to the economic-wellbeing of our planet.

In Britain, the problems caused by invasive non-native plants can affect our lives by, for example:

• Reducing crop yields
• Causing structural damage to roads and homes
• Increasing risks of flooding

It is internationally recognised by the Convention on Biological Diversity that the most cost-effective and least environmentally damaging approach to solving the problems caused by non-native invasive species is by preventing them from getting into the wild in the first place. One way of doing this is to ban the sale of invasive plants. Our governments have the power to ban the sale of invasive plants, but so far they have failed to do so.

Invasive plants damage the environment which is why Plantlife is so concerned about their continued sale. They compete with other plants for light, space and nutrients, often suppressing native flora. They can reduce the light and heat reaching lower-growing plants, alter rates of nutrient cycling, or (in freshwater habitats) cause large fluctuations in oxygen availability, all of which can be harmful to other plants and animals.

The environmental damage caused by invasive non-native plants can be irreversible.

At Lound Lakes on the Norfolk/Suffolk border the threatened native fern, pillwort Pilulariaglobulifera, has been lost whilst the invasive non-native plant New Zealand pigmyweed Crassula helmsii now flourishes. This same invasive species is thought to have led to the loss of the great crested newt Triturus cristatus at a pond in Dorset. The threat posed by New Zealand pigmyweed is considered so great that some ponds are being filled in by conservationists upon its arrival in a new area as a preventative measure intended to minimise damage to other nearby ponds and streams.

There are hundreds of places across Britain where invasive plants are present. The impact of these problem plants varies from site to site. At times it is the social and financial impacts that are most felt, for example when anglers can no longer fish in a river swamped by invasive plants or when the arrival of such plants mean land managers are hit with additional management costs. At other times, the very existence of plant and animal species may be at stake.

Dealing with the problems caused by invasive species (plants, plant pathogens and animals) has been estimated in a Government report to cost our economy around £1.7 billion every single year. We believe the actual cost is far greater as the ‘indirect costs’ associated with invasive species, such as damage to ecosystem service provision, were not accounted for in the report.

How can I help?

It may look pretty, but the water primrose can clog waterways, devastate habitats and cause expensive damage. © Trevor Renals

The simple fact is that more than 60% of invasive plants in Great Britain are garden and garden pond escapees. If we as a nation of gardeners have (inadvertently) caused much of the problem, then the good news is that we can solve much of the problem by the choices we make.

Most invasive plants are still available for sale, with many garden centres, pet shops, aquarists, DIY stores and supermarkets across the country continuing to sell damaging species. Since our governments aren’t using their powers to ban the sale of invasive plants, we need you to use your purchasing power: tell store managers that you don't want to see non-native invasive plants on sale, and don't buy them. Plantlife recommends avoiding non-native invasive plants in the first place is the most effective choice.

Sadly, avoiding invasive plants is harder than it should be. Invasive non-native plants continue to be sold labelled with incorrect or incomplete scientific names, confusing common names (including those generally attributed to native species), and potentially misleading ‘Buy British’ slogans. Take care when buying plants, and ask if you are not sure what you are buying or whether it may be invasive. We believe that all those involved in the production, movement and sale of plants should adhere to the Defra and Scottish Government Horticultural Codes of Practice which outline how plants should be labelled. The codes cite the Consumer Protection from Unfair Trading Regulations 2008 (S.I. 2008/1277) which make it a criminal offence to be misleading about goods being sold.

Over 70,000 different types of non-native plants are grown in Britain. Only a small number of these are already known to be invasive or are thought likely to become so as our climate changes. As a general rule, Plantlife recommends avoiding the following plants (click link below to download):

• List of non-native invasive species to avoid

We believe there are plenty of non-invasive plants available to gardeners, landscapers and pond/fish-keepers. That’s why we have produced a series of booklets to help you choose plants that are less likely to cause problems to the environment should they escape from your garden or pond. For more information click on the 'Plants you can use in place of invasive non-natives' link in the left hand menu

The bottom line:

NEVER release ANY garden or aquarium plants into the wild -

• Don't tip them down land drains,

• Don't dump them in the countryside,

• Don't throw them into your normal waste bin.

Further information

Click on any of the titles below to download a PDF on the subject:

• What is the law regarding non-native invasive plants?
• How do I remove a non-native invasive plant from my land?
• Which species do Plantlife believe are a threat?
• How can I help?
• Can you tell me more about the history and terminology of non-native invasive plants?