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Have you looked carefully at your pond lately?

I only ask because you might have done what a friend of mine did and, in all innocence, bought three plants of a lovely pond plant called parrot feather (Myriophyllum aquaticum) at the local garden centre.

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It's a sweet little thing: light, feathery, ferny leaves and a handy habit of oxygenating the water. Unfortunately, it ate my friend's pond.

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Within a matter of a few months the little side pool she put it in disappeared: then the one next to it went. When it launched a takeover bid for the main pond we had to don the waders and get in there to pull it out by the armful. Three years later, we're still doing it: we've long since surrendered the small pools, finally converted to green feathery carpets some time around 2008.

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The government has just launched the second phase of its campaign to stop you suffering the same fate. Its aim is to educate gardeners about these rampant non-native invaders, but they're not only trying to save the pond in your garden: half-a-dozen of these hugely invasive water plants have jumped the garden fence into our rivers, streams and lakes, choking out other life and covering the lot in green fuzz. It's devastating for native wildlife and costs tens of thousands of pounds every year to eradicate them.

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So I'd advise you to get up from your computer right now and go check whether that lovely little oxygenating plant you popped in your pond this summer is really a monster in disguise. To help you, here's a rogue's gallery of pond plants to avoid at all costs: (click on the images for a larger version)

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Floating pennywort (Hydrocotyle ranunculoides): shiny, kidney-shaped leaves which can grow at a rate of 20cm per day. Download the from the Defra website (PDF)

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Parrots feather (Myriophyllum aquaticum): feathery, delicate, utterly ruthless and spreads like wildfire

Download the from the Defra website (PDF)

New Zealand Pigmyweed (Crassula helmsii): elegant fleshy green leaves like a succulent with tiny white flowers: the tiniest fragment regenerates into new plants. Download the from the Defra website (PDF)

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Water primrose (Ludwigia grandiflora, L. uruguayensis and L. peploides): pretty bright yellow flowers (July - August) which smother a pond in weeks and clamber out onto the banks as well. Download the from the Defra website (PDF)

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Water fern (Azolla filiculoides): tiny, delicate leaves a little like scales: its fragile appearance hides a true monster capable of doubling its weight in two to three days. Download the from the Defra website (PDF)

If, horror of horrors, you find that you do have one of these , don't panic. You can leave it there: just make it part of your autumn pond maintenance to pull out excessive growth. The important thing is to avoid it escaping. Dispose of any you remove on the compost bin or in green bags, and clean your wellies before you go anywhere so you don't inadvertently walk plant fragments out of your garden. Finally, if you've removed water from the pond, dispose of it carefully: watering your plants with it is a safe bet.

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May your ponds stay free of green rugs for many years to come. If they're not, share your experiences in the comments below.

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Visit the website for details of plant and animals species that are not native to the UK.

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Sally Nex is a garden writer and blogger and part of the ³ÉÈË¿ìÊÖ Gardening team.