Sunday, 22 July 2012

Invasive Species

During the summer months our rangers and volunteers spend a great deal of their time controlling invasive plant species.  Invasive plants are robust and fast growing and if not controlled spread rapidly shading out more delicate flowering species.  Many are non-native having been brought here as colourful additions to parks and gardens.  Examples include rhododendron, japanese knotweed and himalayan balsam.

Japanese knotweed

Japanese knotweed grows typically 2m to 3m tall at a rate of up to 10cm a day and is difficult to control as tiny fragments of root can grow into living plants.  The stems are rather like bamboo shoots, the leaves large and and spikes of tiny white flowers are produced in late summer.  It is best treated with a herbicide although even then repeat applications may be required.

Volunteer Mathew pulling himalayan balsam

Himalayan balsam is a member of the bizzie lizzie family and grows rapidly to a height of up to 2m or even more in favourable sites.  The stems are very succulent, the large leaves spear-shaped and pinkish flowers are shaped like an old fashioned policeman's helmet giving rise to its alternative common name.  A shallow root system makes this an easy plant to control simply by hand pulling.


Rhododendron is an evergreen shrub with dark green leaves and attractive large purplish blooms.  We contol this by cutting back stems with saws and loppers and treating the stumps with an herbicide to prevent re-growth.


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