Help weed out the invaders

The Be Plant Wise campaign highlights five of the worst offenders wreaking havoc on our wildlife and waterways.

Gardeners can often unwittingly exacerbate the problem by disposing of unwanted pond plants without composting them properly, throwing out pond water or fish tank water incorrectly, or accidentally introducing species to the wild.

A whole river can be strangled just from one fragment of plant. Fast-growing floating pennywort, New Zealand pigmyweed, water-primrose, parrot's feather and water fern – all of which could be found in a garden pond – are some of those named as posing significant problems in the wild with the potential to cost the nation millions of pounds if they continue to expand at their present rate. Floating pennywort can grow at a rate of 20cm a day in the wild and water primrose can double in size every 15-20 days.

Many of these plants grow to such an extent that they form dense mats which can look like dry land and so pose an additional danger of drowning to people and livestock.

Natural Environment Minister Huw Irranca-Davies launched the public campaign from the banks of the River Wandle in London, which is overrun by floating pennywort.

The Minister said: "From the River Severn to the smallest stream, our waterways are being invaded. We all know about grey squirrels and Japanese knotweed but how many people know that invasive aquatic plants can out-compete native species, choke waterways, harm native wildlife, disrupt the navigation of boats, interfere with recreational activities such as fishing and boating and exacerbate flooding?

"Gardeners can do their bit to help stop the spread by knowing what they grow in their ponds and disposing of unwanted plants with the utmost care. This is vital to halt the spread and prevent our waterways from getting overrun."

The sheer scale of the problem threatening Britain's waterways, wildlife, leisure activities, farming and tourism can be seen in France where water-primrose is known to be present in more than 500 sites, and is the most recent invasive plant to reach Britain's shores.

Across France, control costs run into several million euros a year just to limit its negative impacts, not to get rid of it completely.

Pond owners are advised to:Know what you grow – pick the right plants for your pond and manage them carefully. Choose non-invasive species where possible;

Stop the spread – be careful not to introduce invasive species into the wild, even accidentally, as you could be breaking the law;

Compost with care – make sure you dispose of the whole plant properly and no fragments break away; dispose of waste pond and fish tank water away from streams, rivers, ponds or lakes;

Visit www.direct.gov.uk / beplantwise for more information in England,

or in Scotland visit www.scotland.gov.uk/beplantwise