← Species guide
Himalayan balsam
High riskImpatiens glandulifera
The pink-flowered annual that lines almost every stream in Swansea. One plant throws up to 2,500 seeds and the seed floats, so a single upstream patch reseeds miles of bank.
How to identify it
- Pink to purple 'policeman's helmet' flowers, sometimes near-white
- Reddish, hollow, brittle stems up to 2.5m with swollen nodes
- Long-toothed leaves in pairs or whorls of three
- Seed pods that explode audibly when touched in late summer
Why it matters
- Forms dense single-species stands that shade out native bank plants
- Dies back in winter leaving bare, easily eroded riverbank
- Outcompetes native flowers for pollinators
- Increases flood risk where it collapses into channels
How to control it
- Hand-pull or scythe before flowering — pull below the lowest node
- Always work from the top of the catchment downstream, or you will be reinvaded
- Pulled plants can be left to rot on site if they have not set seed
- Repeat every year for at least 3 years to exhaust the seed bank
- Ideal for community balsam-bashing volunteer days
