Giant hogweed - Ville de Kirkland

Giant hogweed

Giant hogweed

A giant plant to avoid!

Giant hogweed (Heracleum mantegazzianum) is an invasive exotic plant. Its sap contains toxins which, after exposure to the sun, can cause serious skin burns. There have been no cases of giant hogweed detected in Kirkland to date.

How to correctly identify the plant

Giant Hogweed has an alter ego in Quebec, Indian celery or cow parsnip. Smaller in size, the aerial parts of this indigenous plant are much less poisonous (varies according to an individual’s sensitivity). In addition to cow parsnip, certain plants with white umbrella-like flowers can often be mistaken for giant hogweed. That may be the case for angelica, wild carrot, valerian, yarrow, etc. For most people, these plants do not cause dermatitis.

Below are a few characteristics to help you distinguish the two plants:

Giant Hogweed
(Heracleum mantegazzianum)

Indian Celery or Cow Parsnip
(Heracleum maximum)

Plant Height

2 to 4 metres
(6 to 12 feet)

Plant Height

2 metres or less
(3 to 6 feet)


Rigid (5 to 10 cm (2 to 4 in.) in diameter)
Hollow and ridged
Green and purple blotches with coarse white hairs near the leaf junctions


Rigid (5 cm (2 in.) in diameter or more)
Hollow and ridged
Green, covered in fuzzy white hairs and sometimes slight purplish spots


Generally smooth, the leaves can measure up to 1.5m across. The leaf underside is green. Hairs, when present, are stiff and parse.


Smaller, the leaves measure up to 50 cm (2.5 ft) across. The underside is generally covered in soft white hairs for a velvety, light green (greyish) appearance.

If you spot giant hogweed or suspect its presence in the municipality, please contact the eco-counsellor by phoning the Green Line so the plant can be more accurately identified. If the plant is growing on your property, the eco-counsellor will advise you on how to eliminate them.

For more information

For information on health effects and what to do if you have been in contact with giant hogweed sap, contact Info-Santé (8-1-1).
Other reference sites

Ministère du Développement durable, de l’Environnement et des Parcs