Giant Hogweed
Dangerous, Do Not Touch

Do Not Touch - Giant Hogweed Plant If you see this large plant - Do Not Touch!

Currently, Giant Hogweed is not common in Durham Region, but plant sightings are being reported. Giant Hogweed (Heracleum mantegazzianum) is a member of the carrot or parsley family introduced to Europe and North America in the early 1900's. This tall majestic plant might look beautiful but is a significant public health hazard because of its potential to cause severe skin irritation in susceptible people.

The plant sap produces painful burning blisters within 24 to 48Skin Reaction to Giant Hogweed hours of contact.  The plant sap can also produce painless red blotches that later develop into purplish or brownish scars persisting for several years.  Typically your skin is most receptive when it is moist from perspiration and later exposed to sunlight.

Giant Hogweed Fact Sheet (PDF - 600kb)


Giant Hogweed can grow up to 14 feet tall.What Does It Look Like?
The plant can grow from 2.4 to 4.3 metres (8 to 14 feet) tall and key identifying features other than its gigantic size, are as follows:

Flowers - 76.2 centimetres (2.5 feet) cluster forming a white flat topped umbel, with a sheath at the base of the flower. The plant flowers in early to mid summer.   

Stems - 5 to 10 centimetres (2 to 4 inches) in diameter, purple blotched with coarse white hairs around the stem, particularly at the base of the leaf stocks,

Leaves - up to 1.5 metres (5 feet) across and deeply incised, bottom leaves may be compound, while upper leaves only deeply lobed/incised.

Fruit - (which some folks use in dried floral displays again contributing to its spread) are dry, flat and oval about 1 centimetre (3/8 inches) long.
Giant Hogweed StemGiant Hogweed LeafGiant Hogweed Leaf



Giant Hogweed flower cluster


Cow Parsnip is a native plant with similar features and is often mistaken for Giant Hogweed.
Click here to see the differences.


What Do I Do If I See Giant Hogweed Growing In My Municipality, On My Property Or In A Conservation Area?

Central Lake Ontario Conservation is creating a database of Giant Hogweed locations within our watershed. If you have Giant Hogweed or see a plant that fits the description, please take digital photos of the flowers, stem and leaf (Please remember to be very careful to not touch the plant when taking photos) and contact:

Ms. Diana Shermet
Natural Heritage Resource Analyst
Central Lake Ontario Conservation
Ph: 905-579-0411, ext. 107
Email: dshermet@cloca.com

or

the Invading Species Awareness Program
1-800-563-7711
Ontario Federation of Anglers & Hunters

The preferred method of eradication of Giant Hogweed is a herbicide application over 3 to 5 years to exhaust the seeds in the soil.  Pulling or cutting the plant is very dangerous as the plant is juicy with sap, which can become airborne when released.

Consult a licensed professional regarding use of herbicides
and plant removal. 

Cow Parsnip

Cow Parsnip (Heracleum lanatum) is sometimes mistaken for Giant Hogweed. The two main differences are:

1) The stem of Cow Parsnip lacks red blotches.

2) The flower of Cow Parsnip is much smaller than Giant Hogweed.

Cow Parsnip stem lacks red blotchesCow Parsnip flower is much smaller than Giant Hogweed

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