Himalayan balsam: UK volunteers urged to help to battle invasive weed | Plants

Himalayan balsam’s attractive exterior masks a deadly intent. Don’t be fooled by its soothing name, pink flowers and pleasant perfume – according to ecologists, this invasive species chokes our waterways, causes riverbank erosion and is smothering our wild flowers at a terrifying rate.

Determined to stop this nefarious weed from colonising even more of Britain’s lowlands, crack squads of “balsam bashers” have been out regularly since spring, hoping to pull up the evil herb before it has chance to flower.

Cumbria is the latest county to raise an SOS about Himalayan Balsam, with the West Cumbria Rivers Trust asking for volunteers in Mosser, Cockermouth and Loweswater to help vanquish them before they come into flower in mid-July.

Few plants can spread their seeds like the Himalayan balsam, the playboy of the horticultural world. When ripe, its pods explode open, shooting seeds up to seven metres away. With each plant able to produce about 800 seeds, it can easily dominate an area after just one season.

Unlike many other plants, it doesn’t need much light and will grow in a wide range of habitats, shading out other plants. When it dies back in autumn its destructive legacy lives on, leaving waterway banks bare and vulnerable to erosion.

The good news is that unlike other invasive species, such as Japanese knotweed, which can have a root system three metres deep and render a house unsellable, Himalayan balsam is very easy to pull up. Its stout, reddish-translucent hollow stems rarely have roots more than a few centimetres deep and can be lifted out with a pleasing tug.

Charles Hughes, an environmental scientist who leads on a project tackling invasive species for the Canal and Rivers Trust, agrees Himalayan balsam is a handsome menace. Though it has been illegal to plant it or introduce it to the wild in the UK since 1981, it has been causing problems ever since it was introduced to Kew Gardens from Kashmir in 1839.

“It was brought in as an ornamental plant but very quickly dispersed and became a problem soon after its arrival,” said Hughes.

A river cleanup organised by the waterway advocacy group Thames21 in London, removing litter and plants such as Himalayan balsam.
A river cleanup organised by the waterway advocacy group Thames21 in London, removing litter and plants such as Himalayan balsam. Photograph: Dan Kitwood/Getty Images

“The main environmental impact of Himalayan balsam is the fact that because it can grow up to around 2 meters – sometimes a little bit more, very crowded together – it completely shades out our native plants.”

It poses a threat to wildflowers such as purple loosestrife and musk mallow, as well as beloved meadow species such as cowslips.

“When it dies back, it exposes the soil and a lot of riverbanks, so when you come to the wintertime and you get high rainfall, you have huge sediment losses,” said Hughes. “This in turn will cause water quality issues for fish, or otters or waterfowl.”

He suggests those who want to indulge in some balsam bashing download the ID card from the GB non-native species secretariat website to prevent the slaying of innocent plants.

Alex Preston, a lawyer in Manchester, has become a dedicated balsam basher, investing in a fearsome Japanese scythe to help her on her mission to rid her local wetlands of the pest.

She can be regularly found hacking away in Chorlton Ees, an area of woodland and meadows in south Manchester. “I’ve been doing it for about five years, ever since I saw a group of volunteers chopping a big patch down. It’s everywhere in Chorlton Ees, spreading through our wonderful nature reserve and strangling the native plants,” she said. “I bought the Japanese knife to help me on my mission but actually the best way to get rid of it is to pull it up by the roots. It’s strangely satisfying.”

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