Himalayan Balsam (Impatiens glandulifera) is native to the western Himalayas but is now invasive in many parts of continental Europe. It can form dense monospecific stands where individual plants can reach 2 – 3 m in height (one of the tallest annual plants in Ireland). The stem of the plant is smooth, hairless and hollow. They grow upright, easily broken and are usually purple in colour with many large oval-shaped pointed leaves bearing teeth around the edges. The flowers of this plant can vary in colour but are usually shades of white, pink or purple. Flowering usually takes place from June to October. Seed capsules arise where the flowers were and when mature and dry, the slightest touch causes these fruits to split open explosively dispersing seeds up to 20 feet from the parent plant. Seeds are capable of further dispersal by water and animal and human aid.
Manual pulling/cutting, commonly known as 'balsam bashing' is a common method of dealing with Hamalayan Balsam invasions. Pulling should be performed prior to the formation of the seed pods which explode at the slightest disturbance when ripe. Himalayan balsam has a very shallow root making uprooting by hand easy. The pulling technique must be undertaken so that whole plant is uprooted and normally best done if pulled from low down the plant - If snapping occurs at a node the pulling must be completed to include the roots. Uprooted plants can be left to air dry and decompose on a non-permeable membrane. This method is highly suited to dealing with initial outbreaks of the species and in areas where balsam plants are mixed in with sensitive native species.
When not in flower it can be mistaken for Himalayan knotweed, which is another invasive species. It may also be mistaken for Scrophularia nodosa or Scrophularia umbrosa, two native species, which can also be found along riverbanks. Care should be taken that these native species are not eradicated alongside the similar looking Himalayan Balsam.
For information on Himalayan Balsam, see:
- Identification Guide for Himalayan Balsam (Biodiversity Ireland)
- Identification Guide for Himalayan Balsam (Invasive Species Ireland)
- Hamalayan Balsam (Invasive Species Ireland)
For a list of Invasive species, see www.invasivespeciesireland.com