Also known as Indian balsam, this rampant relative of the busy Lizzie was introduced to the UK during the early 20th century as a garden plant. Now it has spread along many of the country’s lowland waterways and locally may totally dominate the vegetation. It is present along all our local rivers. Because it forms dense monospecific stands it is considered a threat to waterside biodiversity. As well as threatening other annual plants, Impatiens may even be able to out-compete native perennial species such as the common nettle!
The success of himalayan balsam is largely due to its extremely high nectar production – for instance about 47 times more than the great willowherb or 23 times more than purple loosestrife. This allows it to attract pollinators such as bumblebees away from native species, so reducing their seed set. For example, seed set in marsh woundwort is reduced by about 25% where it grows mixed with himalayan balsam, as compared to pure patches. Each balsam plant produces up to 2,500 large seeds which “explode” from the ripe seed head and fall to the ground up to several metres away.
If you cut this plant off, it just keeps growing. If you knock it over, it roots from the fallen stem. However, because of its preference for damp ground, it is easy to hand pull as long as you are careful not to break it off. The only problem is that there is always one plant growing right in the middle of an impenetrable bramble patch or halfway down a steep muddy slope. But we are winning! After three years of pulling the plants up before they manage to set seed, there are now fewer and fewer each year.
If you have this dangerous alien on your property, please think about trying to control it. Here are some identification points:
- A succulent fleshy-stemmed annual growing up to 1.5 m tall
- Stems red, somewhat hexagonal in section
- Flowers pink, variable from very pale to quite vivid, even on the same plant
- Leaves opposite, with prominent veins and toothed margins
- Flowering begins about July, seeding begins in late August and continues until the first frosts