Public reminded to stay away from sites with Giant Hogweed

Giant hogweed in full growth near Conna bridge in recent times. (Picture: Lorna Macdonald)

Giant Hogweed (Heracleum Mantegazzianum) is an invasive plant species which grows up to 5 metres tall. It was originally introduced into Ireland over 50 years ago as an ornamental garden plant. It has rough serrated leaves one and a half metres wide, and large umbrella-like flowers that can yield many tens of thousands of viable seeds.

The plant requires ongoing management to keep it under control. Private landowners are responsible for it on their lands and in Limerick, Limerick City and County Council is responsible for managing it when it occurs on land under its management. They are now calling on the public to stay away from any such sites due to the dangers involved. Other public bodies with responsibility for managing land and water courses also have a role to play. 


Giant Hogweed is easy to identify when mature, but more difficult when young. For tips on how to identify it at all stages of growth, and how to distinguish it from our native hogweed (Heracleum Sphondylium) and other similar native species see

Ireland’s climate suits Giant Hogweed perfectly. It favours the damp, open margins of river banks where its seeds can readily disperse downstream.

It is regarded as one of the world’s worst invasive alien plants for the following reasons: 

– It produces a toxic sap in all parts of the plant which can cause a very serious burn that is known as a phytophotodermatitis because the sap is activated by light.

– Its sheer size shades out smaller native plant species and eventually kills them. Because Giant Hogweed seeds are relatively heavy, they tend to fall within a few metres of the parent plant, and this leads to dense infestations of hundreds of plants across a small area. 

– In the winter it dies back. Because there is no native vegetation, soil is exposed and river banks become vulnerable to erosion. 

– One plant can produce a large number of seeds which can disperse downstream if the parent plant is near water. There is also evidence that Giant Hogweed seeds are being accidentally harvested with fodder crops, and may germinate at the location the fodder is taken to. This means that Giant Hogweed can be found in any location. 


Giant Hogweed is controlled by two pieces of European Union legislation: Invasive Species of European Concern (EU Regulation 1143/2014); and EC (Birds and Natural Habitats) regulations S.I.477 (2011) 

For more information visit the Ireland’s Invasive Species website (managed by the National Biodiversity Data Centre). 

You can report any sightings/incidences on