15 May 2023

How can gardeners stop the spread of invasive species?

Tomos Jones

Tomos Jones is the Wales Resilient Ecological Network (WaREN) Project Manager at North Wales Wildlife Trust. He has several years of experience engaging with gardeners on the issue of invasive species as a PhD student at the University of Reading and a Research Fellow at Coventry University.

It’s Invasive Species Week (15 – 22 May 2023) and so a perfect opportunity to look at how gardeners can tackle the issue of invasive species!

What are invasive species?

Many species have been introduced by humans to parts of the world where they wouldn’t naturally be found. Some of these have since spread into the wild where they negatively impact the environment, the economy, our health and the way we live. These species which have an impact are called invasive species. These invasive species are now recognised as one of the top five threats to nature globally, along with: changes in land and sea use, pollution, direct exploitation of organisms (e.g. unsustainable fishing) and climate change. Here we’ll focus on invasive species which have escaped gardens.

Invasive ornamentals

The main source of invasive species globally is their introduction as ornamental garden plants, which has of course been happening for centuries and resulted in a very rich garden flora.

“There are around 70,000 different plants available to buy in Britain according to the latest Royal Horticultural Society (RHS) Plant Finder”.

Most of these are confined to our gardens, but others have managed to escape. In fact, more than half of the flora in Britain and Ireland has been introduced from elsewhere in the world.

Of those ornamentals which have escaped gardens, only a few have (so far) proved to be invasive. They can have impacts such as competing with native species for resources (e.g. light and water), host and spread diseases, and hybridisation – a common example of this being the hybrid between the native bluebell (Hyacinthoides non-scripta) and the invasive Spanish bluebell (Hyacinthoides hispanica).

Further examples of invasive species which originated in gardens include the (famous) Japanese knotweed (Reynoutria japonica or Fallopia japonica) and rhododendron (Rhododendron ponticum). In flower now, are the invasive species three-cornered leek (Allium triquetrum) and red valerian (Centranthus ruber).

Allium triquetrum · © Lisa Toth

How can gardeners stop the spread of invasive species?

The simple answer is: Be Plant Wise! This can be achieved with the three important steps:

  • Know what you grow – consider alternatives to plants known to be invasive (alternatives could be native species).
  • Stop the spread – don’t plant ornamentals, or allow them to grow, in the wild.
  • Compost with care – dispose of garden and pond material (such as roots and seeds) responsibly.

A new guide called Gardening without harmful invasive plants‘ has been released by the GB Non-Native Species Secretariat. This booklet includes information and guidance on how gardeners can avoid invasive plants and suggestions for alternatives.

You can also watch Tomos on the S4C gardening show ‘Garddio a Mwy’ (with subtitles) discussing invasive species in gardens with Meinir Gwilym here.

Become a citizen scientist!

Gardeners can citizen scientists by detecting ornamentals that are showing ‘invasive behaviour’. This could be ornamentals that are spreading too much in your garden. Report any potentially invasive plants to Plant Alert using their online survey. If you live in Anglesey, Conwy or Gwynedd, get involved in our ‘Garden Escapers!’ project. More information here.

This blog has also been published by the University of Reading as a ‘Connecting Research’ blog.