The dirty dozen plants to avoid

Plant and conservation charities are celebrating a government ban on selling five species of invasive and non-native aquatic plants that are choking the life out of ponds and waterways. From this week, water fern, parrot's feather, floating pennywort-which can grow by up to 8in in a day water primrose and Australian swamp stonecrop or New Zealand pygmyweed will be prohibited from sale in England. Although the move was announced last year, retailers were given a year to adjust to the measure.

‘Tough laws to curb the sale of these plants could save the country millions of pounds, as well as protecting wildlife such as fish,' Richard Benyon, the then Environment Minister, said at the time. It was previously illegal to dispose of these plants in the wild, but, now, anyone selling them could face a maximum fine of £5,000 and up to six months in prison.

‘We support the ban,' says the RHS's chief scientist John David. ‘These five species have a very serious impact on river systems and ponds, where fish are often starved of oxygen because these plants form blankets over the top of the water.'

Plantlife, which has long campaigned for a ban, welcomes the move, but wants the Government to do more to reduce the estimated £1.7 billion it says is spent each year trying to control invasive non-native species and has compiled a ‘dirty dozen' (see box). ‘Invasive plants often follow well- trodden paths from garden centre to countryside,' says Trevor Dines, who leads the charity's Welsh branch. ‘People put them in their gardens, but then find them too aggressive and discard them, perhaps through fly-tipping, which gives them the launch pad they need.'

Dr Dines adds that other species, such as cotoneaster, have been scattered by birds: ‘It is the very existence of these species in our gardens and parks that is the biggest problem.' Plant life says most of its hitlist is identified as a risk in the Wildlife and Countryside Act 1981-which makes it an offence to plant, or otherwise cause these species to grow, in the wild-but that hasn't stopped them becoming established.

However, Dr David cautions that the RHS doesn't ‘fully agree with Plantlife's approach': ‘We understand their concerns, but we don't think it's a proportionate response to ban all these species from sale.'

Plantlife's dirty dozen

American skunk cabbage Grows to nearly 5ft, has creeping roots and unpleasant-smelling flowers Spanish bluebell Widely planted and able to cross with our native bluebell, this and its hybrids can now be found in woodland Chilean giant rhubarb With 6ft wide leaves on 5ft bristly stalks, it swiftly renders farmland useless Variegated yellow archangel This innocent-looking dead nettle can smother precious natives, such as spreading bellflower Three-cornered garlic Found along roadsides, hedgerows and woodland and field edges, where it pushes out primroses and violets Hottentot fig Its large flowers make it popular, but it forms impenetrable mats that carpet warm, sunny coastal cliffs Himalayan balsam Can grow to 8ft from seed in a single season and is an aggressive coloniser of river and canal banks Japanese knotweed Can dominate verges, waste ground, riverbanks, woodland, grass- land and coastal areas, and happily grows through concrete Pirri-pirri bur Short, creeping plant that's readily available from garden centres, but becomes especially invasive when it establishes on cool, damp cliffs and upland habitats Rhododendron Planted in Victorian times, it's swept across the UK and crowds out almost all other species Broad-leaved bamboo Easily obtained ‘ornamental' plant that can quickly produce a 6ft by 20ft patch of undergrowth Cotoneasters Only one of this group of shrubs favoured by gardeners is native to Britain-another 70 joined it in the wild after being bird-sown

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