JAPANESE knotweed takes years to get rid of, can grow through concrete and has been compared by actor Tom Conti to sci-fi horror plant the Triffid. 

With lush green shovel-shaped leaves growing from bamboo-like stems, at first glance it looks just like another pretty plant, but hundreds of thousands of people are now discovering the threat posed by the superweed.

Capable of growing a metre in a month, the invasive plant - first introduced here from Asia in the 19th century - is taking over gardens across the land.

And, because it spreads through stem segments rather than seeds, the usual way of dealing with weeds - cutting them back - will just make the problem worse.

According to the Environmental Agency, just 1cm of stem can produce a new plant in only 10 days.

Alternatively, the segments can stay dormant for 20 years before producing new plants.

And that's bad news, not just for other wildlife, but for sheds, garages, pathways, roads and even buildings as the plant's extensive root system is capable of damaging the ground beneath concrete and tarmac before growing up through the resulting cracks.

Chief executive of the Property Care Association (PCA) trade body Steve Hodgson told News Shopper: "The first thing to say is don't be tempted to strim it, dig it up or mess about with it.
"The chances are it will make the problem far worse.

"The way to handle it is to get somebody who understands what it is, where it is and can come back with a responsible, cost-effective strategy to get rid of it."

In household gardens this can often mean using an effective pesticide, treating the leaves so the poison travels down through the plant's system and kills it. But even this can take several years of treatment.

Despite saying some people's mortgages had been affected by the weed, Mr Hodgson stressed he wanted to avoid the scare stories and bring "sanity to the debate".

He said: "It doesn't ususally affect houses that are on decent foundations.

"If you approach it properly, you can eradicate it for a few thousand pounds."

Visit property-care.org for details.

'It can and will take over your garden'

Snigdha Nag, 38, discovered the knotweed growing from an allotment at the back of her Englehart Road, Catford, home in 2009.

She said: "Lewisham Council paid for contractors to kill off the knotweed because when they inspected it, they found a very large patch.

"When we moved into our house we didn't know what this stuff was.

"Initially it wasn't a problem but as it got bigger and stronger it started burrowing under my fence and my shed.

"It managed to grow up through the path we'd laid."

She added: "My advice to people is know how to recognise it quickly. Unless it's a very small patch that you think you can handle, get someone to clear it for you or it can and will take over your garden."

Environment Agency tips

A combination of herbicide treatment and careful excavation should eventually remove the problem.

The most effective time to apply herbicides to Japanese knotweed is in late summer.

A qualified person should carry out the treatment and contractors must have a National Proficiency Tests Council (NPTC) certification.

Herbicide treatment may have to be used for at least three years before knotweed stops growing back.

Contact your council to see if it offers a collection service or have a list of sites which can accept Japanese knotweed waste.

To find out more, visit environment-agency.gov.uk