Vectors of Spread:
General: Giant Hogweed can be identified by the sheer size of it, reaching between 2-5 meters tall, with the lower leaves growing up to 3 meters long and 2.5 meters wide.
Flowers: It has numerous groups of small, white flowers arranged in large (20-50cm in diameter), flat-topped, umbrella-like clusters (umbels).
Stem: Tall (2-5 m), with reddish-purple blotches along the stem. Stems are hollow and coated in coarse bristles arising from blister-like pustules.
Leaves: Similar in shape to a maple leaf, however, much larger in size and deeply incised. Lower leaves can grow up to 3 meters long and 2.5 meters wide.
Seeds: Oval shaped, between 6-10 mm long and have prominent, dark veins.
Roots: Variable – stout, fleshy tuberous root stalks that form perennating buds each year.
Cow Parsnip (Heracleum maximum) is often mistaken for Giant Hogweed. Cow Parsnip is generally smaller (1-2 m) compared to Giant Hogweed (5-6 m).
WARNING: Cow Parsnip also contains a toxic sap that causes severe burns when exposed to sunlight.
Habitat and Origin
Giant Hogweed is native to the Caucasus Mountains in southwestern Asia and was introduced to North America as a garden curiosity due to its size. It may have appeared in a garden near French Creek on Vancouver Island in the early 1960’s and has spread since then.
Giant Hogweed thrives in wet to moist soil, as well as disturbed areas in the lowlands. It is well established in Vancouver and can be found sporadically throughout Squamish and Pemberton. We are currently working on eradicating the plants in the known locations and preventing it from spreading into Whistler.
Propagation and Vectors of Spread
Giant Hogweed propagates solely by seed production. A single plant can produce up to 100,000 seeds, which can remain viable in the soil for up to 15 years. The seeds are winged for ease of dispersal by wind. It generally dies after setting seed.
Giant Hogweed is spread mainly by wind, movement of contaminated soil and seeds floating downstream. Animals also may be accountable for the spreading of seeds.
Economic and Ecological Impacts
Clear, toxic sap is found in all parts of Giant Hogweed. Contact with sap can occur by brushing against the plant, handling plant material, or even by touch tools or mowing equipment that were used for controlling Giant Hogweed.
- The toxic sap can cause burns, blisters and painful dermatitis
- Exposure of sap to eyes may also cause temporary or permanent blindness
- Highly competitive plant due to its vigorous growth early on in the season, its tolerance to shade and seasonal flooding
- Able to co-exist with other aggressive growers
- Increases erosion hazards due to characteristically shallow roots
What Can I Do?
The best approach to controlling the spread of Giant Hogweed is PREVENTION.
Learn to identify Giant Hogweed: use the images presented in this profile page to learn how to identify Giant Hogweed
What to do if you spot it: You can report any Giant Hogweed sightings by clicking here.
- Regularly monitor disturbed and undisturbed sites for infestations
- Ensure soil and gravel is uncontaminated before transport
- Remove plant material from any equipment used in infested areas and wash before leaving the site
- Minimize soil disturbance in area surrounding infestation
- Ensure plants (particularly flowering heads or root fragments) are bagged or covered to prevent spread during transport to designated disposal sites (e.g. landfill)
- Take caution when controlling Giant Hogweed near streams/ ditch lines to prevent the movement of plant parts down stream
**NOTE: due to its highly toxic properties and to ensure that the necessary precautions are taken, it is best to hire a professional to handle Giant Hogweed infestations.
- Purchase, trade or grow Giant Hogweed
- Move soil that has been contaminated with Giant Hogweed
- Unload, park, or store equipment or vehicles in infested areas
Conservation Halton, Giant Hogweed, https://conservationhalton.ca/giant-hogweed
Electronic Atlas of the Flora of BC, Giant Hogweed, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Heracleum%20mantegazzianum
Invasive Species Council of BC, Giant Hogweed, https://bcinvasives.ca/invasive-species/identify/invasive-plants/giant-hogweed
Invasive Species Council of BC, Giant Hogweed TIPS Factsheet, https://bcinvasives.ca/documents/Giant_Hogweed_TIPS_2017_WEB.pdf
Invasive Species Council of Metro Vancouver, Best Management Practices for Giant Hogweed, http://www.metrovancouver.org/services/regional-planning/PlanningPublications/InvasiveSpeciesBMP-GiantHogweed-v4.pdf
United States Department of Agriculture Natural Resources Conservation Service, PLANTS Profile, https://plants.usda.gov/java/reference?symbol=HEMA17
Worksafe BC, Toxic Plant Warning: Severe Skin Damage from Giant Hogweed, https://www.worksafebc.com/en/resources/health-safety/information-sheets/toxic-plant-warning/severe-skin-damage-from-giant-hogweed-heracleum-mantegazzianum?lang=en
For more information on invasive species, check out our resources page.