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Giant hogweed

giant hogweed
Heracleum mantegassianum

There are currently no confirmed cases of giant hogweed in Calgary, but this invasive plant is a weed of serious concern in British Columbia, Ontario and the Atlantic Provinces. Giant hogweed can be a health hazard to humans and animals

What does giant hogweed look like?

Giant hogweed looks extremely similar to another plant species found in Calgary - cow parsnip. A couple of key features can be used in differentiating the two.

Giant hogweed:

  • Large flower (up to 75 cm wide) with 50 or more flower stems or rays.
  • Stems have prominent purple blister-like pustules on the stems.

Cow parsnip:

  • Flower is less than 30 cm wide with only 15-30 flower stems or rays.
  • Stems are green with ridges and fine fuzzy white hairs.

Giant hogweed is also much larger than cow parsnip - it can grow to be several metres tall.

What to do if you see giant hogweed

Do not touch any plant suspected to be giant hogweed, as contact with it can cause burning of the skin, as well as other complications. Similar-looking cow parsnip does not burn the skin but can cause mild skin irritation in some cases.

Visit the Oregon Department of Agriculture's Giant Hogweed Identification site for more information on the differences in giant hogweed and cow parsnip.

The City is actively monitoring for giant hogweed. It is highly recommended to review the information on the giant hogweed to confirm a positive sighting in Calgary. Positive sightings can be reported to 311 or 403-268-CITY (2489) if calling from outside Calgary.