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IN THE past, horticulturalists brought thousands of new plant species from distant lands to the UK, and some have became staples in gardens. A few have spread beyond the fence to grow in the wild and are so vigorous they have taken over local ecosystems.

Well-known examples include Japanese knotweed, which can poke up through asphalt, and rhododendrons, which colonise woodlands, densely covering the forest floor. Purple pampas grass, from South America, loved in many suburban gardens for its huge, showy plumes, is a menace on rocky coasts where it crowds out native species.

Even floating pennywort (pictured), an attractive addition to garden ponds, is now choking some lakes and rivers. Eradication of this is difficult because it can reproduce by regrowing whole new plants from small pieces.

Some of these plants are on , although home gardeners aren鈥檛 obliged to destroy them if they are already growing on their property.

As well as avoiding further damaging introductions, we can all help by joining local control efforts. Where I live, in Greater London, community groups run 鈥渂alsam bashing鈥� walks, where volunteers beat back the Himalayan balsam plants trying to take over the banks of the Hogsmill river. They have to be beaten because pulling them out by the roots could destabilise the riverbank.

Ecologists also want help with their efforts to discover which plant will become the next invasive pest 鈥� and that鈥檚 where home gardeners come in.

It takes an average of 100 years for a non-native plant to spread to the wild from its first use. During that time, home gardeners may have noticed its invasive potential, says Katharina Dehnen-Schmutz at , UK.

She wants today鈥檚 gardeners to sound the alarm about other introduced species that are taking over their flower beds. 鈥淲e ask people to report plants that are spreading in their garden and are difficult to control.鈥�

Along with the , she set up a website called , where people can report invaders. Those in the UK and Ireland can use the resulting .

As well as helping to protect ecosystems, the project may also reduce unhappiness over plant choices. 鈥淕ardeners often say they wish they could have been warned about a certain plant before they bought it,鈥� says Dehnen-Schmutz.

鈥淲e are not saying people should only have native plants,鈥� she says. 鈥淧art of the joy of having a garden is having lots of different plants. We just need to keep an eye on the very few that might become a problem.鈥�

For other projects visit聽newscientist.com/maker.