Giant Hogweed


Municipal Office

395 Mulock Drive P.O. Box 328 Station Main, Newmarket, Ontario
L3Y 4X7

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​​​Giant Hogweed, also known as hogweed, is an invasive plant species that may cause harm to your health and the plant ecosystem. There is currently no proven case of hogweed in Newmarket. There are a variety of plants that are normally mistaken as hogweed.​​

Giant Hogweed identifiersGiant Hogweed

  • Height: 8 to 14 feet tall
  • Leaves: Sharply and unevenly lobed (up to 5 ft. long), hairy below
  • Stems: 2 to 4 inches in diameter, hollow and ridged with purple blotches and coarse hairs
  • Flower: White umbel, 12 to 20 inches wide with 50 to 150 rays, flat-topped​

Negative effects of hogweed

The clear watery sap from hogweed contains toxins that can cause severe burns if the sap touches your skin. The sap can also cause further damage if your skin is exposed to sunlight. Symptoms usually occur within 48 hours and consist of painful blisters. If you come in contact with hogweed: 

  • Wash the affected area with soap and cold water immediately
  • Keep the area away from sunlight for 48 hours
  • Contact your family doctor for questions and/or treatment ​

How does the hogweed spread?

Hogweed seeds produced by the plant can spread along the watercourses, by animals and by people.

Plants normally mistaken as Hogweed

There are a variety of plants that are usually mistaken as hogweed. These include:

Cow Parsnip
  • Height: 3 to 8 feet
  • Leaves: Coarsely and palmately lobed (up to 20 inches. In length and width) with a fuzzy underside
  • Stems: ridged, 2 inches in length and thick at the base, fuzzy hairs with little to no purple spots
  • Flower: White umbel, 4 to 12 inches wide with 15 to 3 rays, flat topped
  • Effects: Can cause irritation to skin
Cow Parsnip
Purple Stem Angelica
  • Height: 4 to 7 feet
  • Leaves: Basal leaves pinnately divided, upper leaves smaller, serrate, pointed.
  • Stems: Purple, round, hollow, smooth, hairless, aromatic.
  • Flower: White/greenish spherical umbel, 4 to 10 inches in width with 20 to 45 rays.
  • Effects: No known harmful effects​
Purple Stem Angelica
Spotted Waterhemlock
  • Height: 3 to 6 feet
  • Leaves: Pinnate with large leaflets
  • Stems: Smooth, purple-spotted
  • Flower: White, numerous umbels and 3 to 6 inches in width
  • Effects: Can be toxic if injected 
  • Height: 2 to 6 feet
Spotted Waterhemlock
Wild Parsnip
  • Height: 2 to 5 feet
  • Leaves: Pinnate, leaflets in pairs along the central stalk
  • Stems: Smooth/few hairs, ridged
  • Flower: Yellow umbels, 2 to 6 inches in width
  • Effects: Sap can cause skin irritation in combination with sunlight
Wild Parsnip
Poison Hemlock
  • Height: 2 to 6 feet
  • Leaves: Lacey, fern-like, pinnate
  • Stems: Ridged, purple-spotted, hairless
  • Flower: White, numerous flat umbels, 1.5 to 2.5 inches in width
  • Effects: Plants are toxic if ingested
Poison Hemlock

Report hogweed sightings


If you suspect hogweed on Town of Newmarket property, please contact the Town of Newmarket at 905-895-5193. Newmarket's By-laws department will will go out to inspect the plant and determine if it is hogweed. If you suspect hogweed on your private property, please contact a professional to remove the plant. ​

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