Himalayan Balsam (Impatiens glandulifera) is known to many people as an attractive plant with a familiar sweet scent, and a reputation for being a good nectar source for bees. However, despite the plant being valued for these reasons, Himalayan Balsam is actually one of the most problematic weed plants that we have in the UK.
It is a non-native species that was brought to the UK in 1839 from its natal habitat in the Western Himalayas. It goes by several names including Kiss-me-on-the-mountain, Indian Balsam and Policeman’s Helmet, amongst others, but is distinctive in its appearance, having pink flowers, oblong jagged-edged leaves and a pink tinged succulent stem. The green seed pods are also quite unique, holding up to 16 seeds each, which they can fling up to 7 metres away when touched. One Himalayan Balsam plant is said to be able to spread 2,500 seeds alone!
It is therefore no surprise that it has spread so successfully and is now common all over the UK. As it is so fast growing and can survive in shallow soil, few of our native wild flowers can compete with it, and none of our wildlife eats enough Balsam to be able to prevent it from dominating in the environment.
Himalayan Balsam grows particularly well in damp places, and is commonly found spreading along river banks where its seeds can float downstream and colonise new areas. It grows up to 3 metres high, shading out the plants beneath it so that only crowds of tall Balsam are left growing. When these die out in the autumn, the ground is left bare and vulnerable to erosion.
In the UK it is illegal to plant Himalayan Balsam in the wild or to allow it to spread into the wild. The plant can be eradicated by licenced practitioners using chemical control in certain places, but this is limited to places that are not near water. This method may also result in non-target plants being killed.
Cutting or slashing the Himalayan Balsam low to the ground is also an option, but mostly Balsam is pulled from the ground by hand. This manual method is easy because the plants have shallow roots, but this is very time consuming and needs to be done ideally before they start to flower, and always before they seed.
The seeds only survive for up to 18 months in the seedbank so it is estimated that Himalayan Balsam can be removed completely from an area within 2 years if repeated control efforts are made and there is no re-introduction of the plant from nearby sites. Unfortunately this is very rarely the case, as widespread or catchment scale control of the plant is very hard to coordinate, especially as it needs to be repeated over several years to prevent seeds in the soil from repopulating the areas that have been cleared.
Traditional methods are inadequate for stopping the spread of Himalayan Balsam in the UK. Using the methods we currently have, the Environment Agency has estimated the cost of eradication of Himalayan Balsam from the UK would be around £300 million. CABI have identified a rust fungus (Puccinia komarovii var. glandulifera) from the Himalayas which has been shown to weaken Himalayan Balsam and reduce its competitive advantage. In spring 2015 CABI carried out a nationwide rust release and monitoring programme, which included 4 sites in Wales. The results were more limited than those observed in the field in the Himalayan native range and currently much more research is needed to determine which factors could help to spread infection between Himalayan Balsam plants here in the UK. However, there is certainly a chance that this bio-control method could help to reduce spread of Balsam and CABI are planning for a full country-wide release programme in 2017.
To eradicate the Himalayan Balsam from our Nature Reserves the Wildlife Trust of South and West Wales has been holding annual ‘Balsam Bashes’ with groups of volunteers to manually remove the plants from the ground. At the moment, this is the best defence we have against the spread of Balsam, so it is vital work if we want to continue to see our native wildflowers in bloom.
Hopefully the future holds a better solution for controlling this invasive plant in the UK, but for now, we need all the help we can get.
Visit our events page to learn more about volunteering to help us remove Himalayan Balsam, or email Lorna on email@example.com to find out other ways to help.