Introduced from the Himalayas as a garden ornamental in the mid 1800’s it is related to the garden plant Busy lizzie and commonly known as policeman’s helmet. In the mid-summer it produces attractive pink flowers which develop into seed pods that explode shedding thousands of seeds in the late summer. The seeds survive the winter in the soil and germinate the following spring forming dense carpets of seedlings that mature into adult plants.
Balsam is now widespread across the UK forming large dense stands that exclude native species in lowland wetlands, riverbanks, and damp woodlands. When it dies back in the winter it can leave riverbanks exposed to erosion during heavy rainfall, which can impact on watercourses and increase flood risk. The seed can also survive transportation via watercourses making it a highly invasive weed.
Since its introduction in the early nineteenth century, the Himalayan Balsam has spread wildly in the United Kingdom. As a result, the species is listed under the Schedule 9 of the Wildlife and Countryside Act (1981) rev. 2, meaning it is an office to plant or cause the spread of the species.
Successful management within a site requires controlling the weed, seed and movement of soil. Contaminated soils can be removed offsite by a licenced waste carrier ensuring the removal of all life stages. Alternatively, the weed can be managed using herbicides during the spring and early summer (i.e. before flowering) over several seasons until the seed-bank has been depleted. What is difficult is controlling re-establishment if there are sources of seed further upstream which where a whole catchment level management plan is advantageous.
