Himalayan balsam is a large annual plant, native to the Himalaya mountain region in Asia. It can form dense monspecific stands where individual plants can reach 2 - 3 m in height (one of the tallest annual plants in Ireland). The aggressive seed dispersal, coupled with high nectar production which attracts pollinators, often allows the Himalayan Balsam to outcompete native plants. In Britain, Himalayan Balsam is regarded as one of the top-ten most wanted species that have caused significant environmental impact.
This species grows in dense monospecific stands along the banks of rivers and effectively suppresses any native grasses and herbaceous plants. The Balsam dies back from October onwards, exposing the now bare bank-sides to erosive winter flows and floods. Soil erosion from winter flows is damaging to spawning fish (lamprey and salmon). The higher nectar production in the flowers also makes the plant more attractive to bees resulting in less pollination of our native species.
After flowering between June and October, the plant forms seed pods 2-3 cm long and 8 mm broad, which explode when disturbed, scattering the seeds up to 7 m from the parent plant. Seeds are capable of further dispersal by water and animal and human aid.
This annual plant grows to 3 m high. The stem of the plant is smooth, hairless and hollow. They grow upright, are 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, with a hooded shape, 3 -4 cm tall and 2 cm broad.