Property, Gardens & Trees

Giant Hogweed

Giant Hogweed is a non-native invasive plant that poses a serious threat to human health and natural ecosystems. We have found this plant along Spencer Creek and roadways in Dundas. Some plants have been found on private property in Dundas and Flamborough. If you find Giant Hogweed on your property, call 905-546-2489.

How to identify Giant Hogweed

Giant Hogweed looks similar to cow parsnip. It can grow to impressive heights and blossoms.

Typical traits of Giant Hogweed:

  • 1 to 5.5 metres in height (3 - 15 feet)
  • Large, deeply cut leaves with sharp coarse teeth, reaching widths in excess of 1 m (3 feet)
  • Stems are covered in coarse whisker-like hairs, with red-purple spots
  • White, umbrella shaped flowers up to 1.2 m (4 feet) across
Photo courtesy of Credit Valley Conservation

Health effects

Giant Hogweed’s leaves and stem produce a watery sap containing a chemical, which makes human skin highly sensitive to the sun and other sources of ultraviolet light. Touching the plant or brushing against it is enough to cause serious injury. Exposed to sunlight, the sap causes painful blistering within a few hours of contact. The healing process can be slow, and your skin may remain sensitive to sunlight for the rest of your life. Blindness may occur if the sap gets into your eye.

If any sap touches your skin:

  • wash the affected area immediately with soap and water
  • keep the affected area out of the sun
  • see your doctor if you have a reaction

For your own safety, we encourage you to contact a licensed weed exterminator to remove Giant Hogweed from your property. 

Do not compost Giant Hogweed. Do not put Giant Hogweed out as leaf and yard waste or in your green bin. It is accepted in the garbage if sealed in a bag (no dirt).

The City has received approval from the Ontario Ministry of the Environment to eradicate Giant Hogweed on road allowances and City maintained trails using a spray herbicide. Red signs warning of herbicide use are posted when used for Giant Hogweed.

If you find Giant Hogweed in parks or on trails, call 905-546-2489.