Also known as Indian balsam, this rampant relative of the busy Lizzie was introduced to the UK during the mid 19th 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!
Mature plants are typically 1.5 m to 2 m tall, but they can reach up to three metres, making this the tallest annual growing wild in Britain. As well as over-shading native plants, 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. Impatiens, meaning “impatient”, refers to this method of dispersal.
As an annual, and with few or no viable seeds persisting in the soil for more than a year, the way to control Himalyan balsam is to prevent it seeding. However, if you cut it anywhwere above the lowest node on the stem it just keeps growing. If you knock it over, it roots from the fallen stem. But because of its preference for damp ground and rich soils, 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.
If cutting rather than pulling, it is important to cut the stem as low as possible - beneath the first node. You can do the job with a slasher, but a scythe is better as long as the terrain is suitable. Given that the terrain is often not perfect, though, it may be best to use a ditch blade (shorter and more robust) instead of a grass blade.
This is not an advertisement, just a link to The Scythe Shop, importers and suppliers of what is probably the best tool for clearing both balsam and bracken, as long as there aren't too many obstructions in the way.
Balsam seeds are known to spread to new areas in mud on people's footwear, so anyone doing “balsam-bashing” late in the season, when it has already started to produce seeds, should check their boots before leaving the work site!
If you have this dangerous alien on your property, please think about trying to control it. Here are some identification points:
- A tall, succulent fleshy-stemmed annual
- Stems somewhat hexagonal in section, hollow, red in upper parts of the plant
- 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