We often here of alien plants running wild in the countryside. Where have they come from and why are they here

A.� There are scores of plants, both land and water-based running amok in Britain and it is basically down to us, the gardeners.

�

As a gardening potty nation we've never been satisfied with our native flora and fauna, and have been importing plants from around the globe for centuries. Just think back to the great plant hunting exploits of the likes of Joseph Banks with Captain Scott on the Endeavour. Plants came from South America, the Indian sub-continent, Australasia and were a symbol of British Empire status around the world and later Empire.

�

A.� Once they have escaped into the wild they are no longer subject to the control of gardeners, and face none of the competition or natural predators that keep them in check in their native countries.

�

Take the dreaded Japanese Knotweed, for instance. In Japan rarely gets to be more than a medium size shrub on account of other dominant plants in the wild and a variety of insects and fungal diseases that attack it. Here none of those elements are present so it has grows away unhindered.

�

A.� Not at all, in fact in Australasia and the Americas, for instance, they have multi-million pound eradication projects for alien invasives, including the use of bio-controls (introducing predators from the plants country of origin).

�

Perhaps the most famous example was in Australia in the 1920s, when the Prickly Pear cacti, introduced as a decorative garden exotic from South America, found the outback so much to its liking it was swallowing up millions of acres of prime farmland at an astounding rate. It was finally defeated by releasing an Argentinean moth that buries into the cactus to lay its young, which then feed on the plant.

�

A.� The problems with the likes of Japanese Knotweed (Fallopia japonica), Himalayan Balsam (Impatiens glandulifera) and Giant Hogweed (Heracleum mantegazzianum) are well known, and it now illegal to sell, plant or spread it.

�

Conservationists' concern has now switched to a number of aquatic plants that are choking rivers, streams and canals, but are still, amazingly, legally sold through garden centres (although many have voluntarily withdrawn them). Those to avoid are New Zealand Pigmyweed (Crassula helmsii), Parrot's Feather (Myriophyllum aquaticum) and Floating Pennywort(Hydrocotyle ranunculoides), all of which can grow at a rate of between 10-15cms per day.

�

Others now on the wanted list include the Water Hyacinth (Eichornia crassipes), Water Chestnut (Trapa natans) and Exotic Water Lettuce (Pistia stratiotes). If you are in any doubt check with the nursery or garden centre and where possible plump for native species.

�

A.� Probably your best starting point is the local Environment Agency office, which you'll find in the telephone book. The charity Plantlife are leading the campaign to ban the sale of many invasive plants and will be able to send you literature on problem plants and how best to deal with them. You can call them on 020 7808 0100.

�