Giant hogweed

Giant hogweed is an invasive biennial or perennial plant. It reaches a height of 10 to 15 feet (three to four metres) when in flower and has hollow stems, two to four inches (five–ten centimetres) in diameter with dark reddish-purple spots and bristles. Giant hogweed flowers mid-May through July, with numerous white flowers clustered in an umbrella-shaped head that is up to two and a half feet (0.75 metres) in diameter across its flat top. Giant hogweed is originally from Asia and was introduced in Ontario as an ornamental plant.

A public health hazard, giant hogweed’s clear, watery sap has toxins that cause photo-dermatitis. The sap of the giant hogweed, along with sunlight, can cause skin inflammation, burns and in serious circumstances, blindness if the sap gets into an eye. It is harmful to both people and pets. Children should be kept away from giant hogweed, and protective clothing (including eye protection) should be worn when handling it or digging it.

How to identify giant hogweed

You can tell if the plant is a giant hogweed by its tall growth and thick stem with reddish spots. It looks like giant Queen Anne’s lace or wild carrot but is considerably larger. It is important to note that other plants in our green spaces look like giant hogweed as well. Angelica and Cow Parsnip have a very similar leaf pattern and flower as giant hogweed. Angelica may be found in gardens grown as an herb while many farmers may be familiar with Cow Parsnip, which have been found in farm fields for decades.

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The plant is most commonly recognized when they have their large flowering stalks. They tend to grow in open, undisturbed sites with abundant light, but can be found in woodlands or partially shaded forest edges.

Please stay on established paths in City parks and trails to avoid coming into contact with Giant Hogweed

Treatment

Those exposed to giant hogweed should:

  • wash the affected areas immediately, with soap and water if available;
  • keep affected areas out of direct sunlight;
  • seek medical advice as soon as possible.

What to do if you find giant hogweed in your backyard

  • The safest method to remove this plant from your property may be to call a professional service.
  • Wear protective clothing, including gloves, long sleeves, pants, and eye protection, rain coat and boots
  • Avoid getting sap on your skin
  • Immediately remove any flower heads to prevent seed growth and dispersal
  • Sever the plant roots 3 – 5 inches (8 – 12 cm) below the soil surface
  • Dispose of all plant parts in a double-bagged garbage bag, seal the bag and do not compost or put it in your yard waste
  • Return to the plant site periodically to remove any new plant growth
  • Wash the clothes you wore to remove the plant afterwards
  • For effective control, the plant should not be mowed, but rather sprayed with an herbicide at intervals until it is gone. Even after the parent plant is completely removed, the numerous seeds left behind can germinate seven to 15 years later, and ongoing monitoring is required.

For more information or to report giant hogweed

To help us verify the identification please take a high quality photo from a safe distance away and share with parks@guelph.ca. Please include a detailed description of the location of the location of the plant in your email.

Parks Operations and Forestry
519-837-5626
parks@guelph.ca

Remember, if you see it, DON’T TOUCH IT.