Wednesday, 26 November 2014

Japanese Knotweed, Himalayan Balsam and Giant Hogweed can cause Asbos and fines for failure to control their growth.



The Anti-Social Behaviour, Crime and Policing Act 2014 has issued new laws concerning Japanese knotweed, Himalayan balsam and Giant Hogweed. Asbos or fines from £2,500-£20,000  will now be given to people who fail to control the spread of these destructive plants in residential areas.  

Anti-social behaviour orders/Asbos have up to now often been associated with young delinquents involved in drunken behaviour, intimidation, disturbing the peace etc so these serious measures may seem drastic and surprising.


                                                            Impatiens Glandulifera
                                                              Himalayan Balsam

The three plants were originally brought back from foreign parts by intrepid plant hunters in 1839 for their "herculean proportions" and "splendid invasiveness" and as Wikipedia , tongue in cheekily puts it, so that "ordinary people could buy them for the cost of a packet of seeds to rival the expensive orchids grown in the greenhouses of the rich."

Unfortunately the plants grow so strongly they smother our native plants, damage forestry, agriculture, concrete, tarmac, flood defences and the stability of river banks. Japanese knotweed is the most pernicious: it cost £70 million to clear the London Olympics site before building could begin. Mortgage applications have been refused until it is cleared from the garden or neighbouring garden and houses have lost their value as a result.

Nonetheless Jeff Howell in the Daily Telegraph reports that the glyphosate weedkiller "Roundup" can keep Japanese Knotweed under control. Spraying seawater on the plants has had good results in trials in the Queen Charlotte Islands of British Columbia. 

Many people are unaware what Japanese knotweed, Himalayan balsam and Giant Hogweed look like. 




  • has spade-shaped leaves arranged in a zigzag pattern along the hollow stem
  • produces fleshy red tinged shoots when it first breaks through the ground
  • can form dense clumps that can be several metres deep
  • produces clusters of cream flowers towards the end of July 
  • dies back between September and November, leaving brown stems
  • contains oxalic acid, which when eaten may aggravate conditions such as rheumatism, arthritis, gout, kidney stones or hyperacidity.
  • can lead to severe blistering and scarring after handling the sap

 Himalayan Balsam

  • can grow up to 10 ft
  • has reddish coloured stems
  • has dark green, lance-shaped leaves with jagged edges
  • flowers from June to October
  • has large, brightly coloured flowers that are usually in variable shades from purple to pale pink
  • can produce around 2,500 seeds per plant each year
  • has explosive seed pods that can throw seeds over 6 metres away from the plant
  • in late autumn the plants die back leaving the area bare of vegetation and liable to erosion
  • Cornish trials have shown that Himalayan Balsam seeds only remain viable in the soil for 1 year. Therefore, if effective control is carried out before seeding, complete eradication can be achieved in one season.
  • Strimming or cutting is an effective control

Heracleum mantegazzianum
  • is a large member of the carrot family, 
  • can grow to more than 15 ft 
  • has sap  which causes phytophotodermatitis in humans, resulting in blisters, long-lasting scars, and even blindness. 
  •  resembles native cow parsley or hogweed. It can take four years to reach its full height of 3-5 metres and flower. 
  • has a reddish purple stem with fine spines that make it appear furry - like a stinging nettle
  • has hollow stems
  • has spotted leaf stalks
  • has leaves up to 1.5 metres wide
  • flowers in June and July
  • has flower heads that are usually 50 centimetres wide - each flower head is capable of producing 50,000 seeds every year
  • has seeds that can stay in the soil for several years before they develop
  • Grows generally near watercourses, in damp meadows and on waste ground
  • See Cornwall Council's tried and tested methods for control and guidance