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Japanese knotweed is a strong-growing, clump-forming perennial, with tall, dense annual stems. Stem growth is renewed each year from the stout, deeply-penetrating creeping underground stems.

It is an attractive plant but is a real problem as it spreads rapidly. In winter the plant dies back beneath ground but by early summer the bamboo-like stems grow to over 2.1m (7ft), suppressing all other growth. To get rid of it completely is difficult as it is very hard to remove by hand or with chemicals and although it can be dealt with by the homeowner, it is advised that it is dealt with by professionals.

New legislation now covers its control – see below.

New legislation:

An amendment to the Anti-social Behaviour, Crime and Policing Act 2014 includes Japanese knotweed and other invasive non-native plants. Full details of how this will work for the homeowner are not yet available, but here are some key points:

• It is not illegal to have Japanese knotweed in your garden 

• On your property, you should aim to control this plant and other invasive non-native plants such as Himalayan Balsam and Giant Hogweed, to prevent them becoming a problem in your neighbourhood. If they have a "detrimental effect of a persistant or continuing nature on the quality of life of those in the locality", the legislation could be used to enforce its control 

• Control can be carried out by the homeowner (see the control section below) and doesn't require a specialist company. However, a specialist company will be skilled at control and can dispose of the plant waste 

• Identification is important. Japanese knotweed can be confused with other plants including Persicaria microcephala (e.g. P. microcephala 'Red Dragon'), Leycesteria formosa and Houttuynia cordata (see below)

• Where problems with Japanese knotweed occur in neighbouring gardens, we suggest that you speak or correspond directly with your neighbours (who may already be taking action to control this difficult weed). These informal steps should be taken before contacting your council to talk about control using the legislation 

Appearance:

In spring and summer, bamboo-like shoots grow to 2.1m (7ft) tall. Leaves are up to 14cm (5½in) in length and the creamy-white flower tassels produced in late summer and early autumn reach up to 15cm (6in).

For information on eradication and professional help, please see links below:

For more information, visit:   Royal Horticultural Society  or  Cornwall County Council

Above information on Knotweed from the Royal Horticultural Society website.