← Species guide
Giant hogweed
Highest riskHeracleum mantegazzianum
The one that hurts people. Its sap makes skin blister badly in sunlight, and the burns can recur for years. Children are most often affected because the hollow stems look like play material.
How to identify it
- Enormous — 3 to 5m tall when flowering
- White umbrella-shaped flower heads up to 60cm across
- Thick green stems with purple blotches and coarse white bristles
- Huge jagged, deeply divided leaves up to 1.5m wide
Why it matters
- Phytotoxic sap causes severe blistering and long-term light sensitivity
- Shades out all ground flora, leaving bare eroding soil
- Dominates riverbanks and reduces access to fishing and paths
How to control it
- Never strim or mow it — that aerosolises the sap
- Cover skin and eyes fully; treat any contact as a chemical burn and keep it out of sunlight
- Cut the tap root 10–15cm below ground in spring on small stands
- Glyphosate on young foliage in spring, repeated over several seasons
- Remove seed heads before they ripen to stop the next generation
