Gardening: Attack of the killer weed

The Kiwi cousin of the Bitter Cress weed is threatening to strangle our gardens. Ursula Buchan offers advice on how to identify and eradicate this deadly plant

I don't want to sound like Corporal Jones in Dad's Army, running round in a tizz shouting "Don't panic", but I think you ought to know that there is an aggressive alien weed now on the loose in British nurseries, which has the capacity to make our gardening lives far more difficult.

If we all take some care to refuse it entry into our gardens, and eradicate it if it does appear, there will be no problem; if not, we are in for a wearing time.

The weed is the New Zealand bitter cress, Cardamine corymbosa, very similar in appearance to our native "hairy bitter cress" - which explains why it has spread so stealthily. Our British native version is maddening enough, germinating as it does all year round in mild seasons, growing in any soil, however poor, running up to flower and seeding in just a few weeks, and sending out explosions of seeds whenever you brush against it. Fortunately, however, it is easy enough to pull up by the stem, for it is an annual.

The New Zealand version is not so amenable, though. It appears to be perennial, with a persistent, flat crown of pale green, round leaves, which are held opposite each other on long stalks. It has an inch-long stem with the usual four-petalled white flowers and one or more taproots. If you try to pull the plant up, the stems usually break off at soil level, leaving the roots behind in the soil, and thus being capable of sprouting once more.

That is the secret of its success, and the reason why it is currently causing nurserymen from Scotland to the West Country to tear their hair out. It colonises plants in pots very quickly, particularly in polythene tunnels, and the fear is that however careful nurseries are (and it is certainly in their interest to wage a war against it), this weed will inevitably be passed on to customers and end up in private gardens.

Charlotte Evans, of Waterwheel Nursery near Chepstow, has become so concerned recently at the probable country-wide spread of this alien weed that she has started a public-spirited campaign to alert both nurserymen and the general public to the menace.

She has learnt that the weed was introduced from New Zealand in 1975, to the Royal Botanic Gardens in Edinburgh, and probably also elsewhere in Scotland, and that it is now widespread in Scottish nurseries, from whence it has made its way south, and also across the water to Holland.

In one alpine nursery in the Midlands, I have seen how this weed has successfully colonised small pots, topped with grit; it is extremely difficult to clean off without pulling out the grit and disturbing the pot's true occupant. If you touch the seed-heads, they explode, sending seed several feet into the air.

This bitter cress sets seed by mid-April in nursery polytunnels, and by mid-May outside, so if you are buying plants from garden centres or nurseries now, you should be aware that you may be bringing it home with you.

If you see a cress-type weed in the pot which will not pull up easily, remove it with a sharp knife, digging down into the compost so that you prise up the entire root. Then, just in case there are seeds on the surface that are ready to germinate, remove the top half an inch of compost from the pot, put it into a bag, and then place the bag safely in the dustbin.

Should you then find that the weed does get a hold in the garden, dig up each plant you see with a hand-fork or knife, again being very careful to remove every bit ofthe taproot, Tell all your friends to look out for it, too, and take care when you pass on plants to them. But, whatever you do, don't panic.

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment
Nick Hewer, Lord Alan Sugar, Karren Brady are returning for The Apprentice series 10

TV
Arts and Entertainment
There has been a boom in ticket sales for female comics, according to an industry survey

comedy
Arts and Entertainment
Angelina Jolie and Winona Ryder star in 'Girl, Interrupted'

TV
Arts and Entertainment
From left to right: Ed Stoppard as Brian Epstein, Sheridan Smith as Cilla Black and Elliott Cowan as George Martin in 'Cilla'

TV
Arts and Entertainment
Thomas Pynchon in 1955, left, and Reese Witherspoon and Joaquin Phoenix in Paul Thomas Anderson's adaptation of his novel, Inherent Vice

film
Arts and Entertainment

TV
Arts and Entertainment
Singer Nicole Scherzinger will join the cast of Cats

theatre
Arts and Entertainment
Fans were left surprised by the death on Sunday night's season 26 premiere

TV
Arts and Entertainment
Emma Watson has become the latest target of the 4Chan nude hacking scandal

film
Arts and Entertainment
Lady Mary goes hunting with suitor Lord Gillingham

TV
Arts and Entertainment
Nick Dunne, played by Ben Affleck, finds himself at the centre of a media storm when his wife is reported missing and assumed dead

film
Arts and Entertainment
Lindsay Lohan made her West End debut earlier this week in 'Speed-the-Plow'

theatre
Arts and Entertainment
Artist Nathan Sawaya stands with his sculpture 'Yellow' at the Art of Brick Exhibition

art
Arts and Entertainment
'Strictly Come Dancing' attracted 6.53 million viewers on Friday
tv
Arts and Entertainment
David Tennant plays Detective Emmett Carver in the US version on Broadchurch

tv
Arts and Entertainment
The Doctor goes undercover at Coal Hill School in 'The Caretaker'
tv
Arts and Entertainment
Ni , Rock of Rah, Vanuatu: The Ni live on one of the smallest islands of Vanuatu; Nelson flew five hours from Sydney to capture the 'isolation forged by their remoteness'
photographyJimmy Nelson travelled the world to photograph 35 threatened tribes in an unashamedly glamorous style
Arts and Entertainment
David Byrne
musicDavid Byrne describes how the notorious First Lady's high life dazzled him out of a career low
Latest stories from i100
Have you tried new the Independent Digital Edition apps?

ES Rentals

    Independent Dating
    and  

    By clicking 'Search' you
    are agreeing to our
    Terms of Use.

    Italian couples fake UK divorce scam on an ‘industrial scale’

    Welcome to Maidenhead, the divorce capital of... Italy

    A look at the the legal tourists who exploited our liberal dissolution rules
    Tom and Jerry cartoons now carry a 'racial prejudice' warning on Amazon

    Tom and Jerry cartoons now carry a 'racial prejudice' warning on Amazon

    The vintage series has often been criticised for racial stereotyping
    An app for the amorous: Could Good2Go end disputes about sexual consent - without being a passion-killer?

    An app for the amorous

    Could Good2Go end disputes about sexual consent - without being a passion-killer?
    Llansanffraid is now Llansantffraid. Welsh town changes its name, but can you spot the difference?

    Llansanffraid is now Llansantffraid

    Welsh town changes its name, but can you spot the difference?
    Charlotte Riley: At the peak of her powers

    Charlotte Riley: At the peak of her powers

    After a few early missteps with Chekhov, her acting career has taken her to Hollywood. Next up is a role in the BBC’s gangster drama ‘Peaky Blinders’
    She's having a laugh: Britain's female comedians have never had it so good

    She's having a laugh

    Britain's female comedians have never had it so good, says stand-up Natalie Haynes
    Sistine Chapel to ‘sing’ with new LED lights designed to bring Michelangelo’s masterpiece out of the shadows

    Let there be light

    Sistine Chapel to ‘sing’ with new LEDs designed to bring Michelangelo’s masterpiece out of the shadows
    Great British Bake Off, semi-final, review: Richard remains the baker to beat

    Tensions rise in Bake Off's pastry week

    Richard remains the baker to beat as Chetna begins to flake
    Paris Fashion Week, spring/summer 2015: Time travel fashion at Louis Vuitton in Paris

    A look to the future

    It's time travel fashion at Louis Vuitton in Paris
    The 10 best bedspreads

    The 10 best bedspreads

    Before you up the tog count on your duvet, add an extra layer and a room-changing piece to your bed this autumn
    Arsenal vs Galatasaray: Five things we learnt from the Emirates

    Arsenal vs Galatasaray

    Five things we learnt from the Gunners' Champions League victory at the Emirates
    Stuart Lancaster’s long-term deal makes sense – a rarity for a decision taken by the RFU

    Lancaster’s long-term deal makes sense – a rarity for a decision taken by the RFU

    This deal gives England a head-start to prepare for 2019 World Cup, says Chris Hewett
    Ebola outbreak: The children orphaned by the virus – then rejected by surviving relatives over fear of infection

    The children orphaned by Ebola...

    ... then rejected by surviving relatives over fear of infection
    Pride: Are censors pandering to homophobia?

    Are censors pandering to homophobia?

    US film censors have ruled 'Pride' unfit for under-16s, though it contains no sex or violence
    The magic of roundabouts

    Lords of the rings

    Just who are the Roundabout Appreciation Society?