Himalayan balsam (Impatiens Glandulifera) was introduced in 1839 by Victorian plant hunters, and it quickly escaped into the wild to become one of the UK’s most non-native invasive weeds.
It is a relative of the “Busy Lizzie” and thrives in wet habitats close to rivers, streams and ponds. The Victorians may have been attracted by the colour of the flowers, which is shown in the photograph, as well as the speed at which the plant grows and adapted to our temperate climate.
Recent voluntary conservation work completed in June and July 2024 with Surrey Wildlife Trust on Whitmoor Common revealed that the plant is capable of growing at a very high density, with as many as 50 separate plants growing in a square metre. These dense stands can shade out and prevent native plants from growing, thus reducing the biodiversity of the area.
Therefore, management on Whitmoor Common is necessary due to the high status of the heathland. The easiest way to manage Himalayan balsam, though labour intensive, is by pulling the individual plants out, since their root systems tend to be small relative to the size of the plant. This process is easy, especially if the ground is moist after a period of rainfall, but needs to be done on an annual basis in order to prevent the spread of the plant.
Himalayan balsam has a colourful flower, often pink or white. However, the problem is that these flowers are capable of producing exploding seed pods with as many as 800 individual seeds which can be scattered up to seven metres from the plant. Seeds will germinate two or three years after the original dispersal. If the plant is found close to rivers or streams, seed dispersal is eased by the flowing water, which helps to explain the ubiquitous location of this invasive weed along UK rivers and streams.
The plant produces sugary nectar, often more than other flowering native plants, and consequently it is more attractive to bees and other insects, often leaving other flowering plants unpollinated. In this context it is worth viewing the video clip on YouTube titled “Bees on Himalayan Balsam - Ghost Bees”.
Himalayan balsam grows very quickly, often reaching a height of 2 to 3 metres during the growing season. When it dies back, it can leave river banks without any vegetation, thus making them more vulnerable to erosion.
Since Himalayan balsam is one of the most invasive plants in the UK, the Wildlife and Countryside Act of 2011 made it an offence to introduce Himalayan balsam into the wild. Bearing in mind the range of problems this plant causes, the work being done by SWT and the volunteers over a number of years is clearly beneficial to Whitmoor Common.
By Richard Seymour
Volunteer, Surrey Wildlife Trust and Friends of Chitty's Common