Giant hogweed

Species

Heracleum mantegazzianum

Giant hogweed (Heracleum mantegazzianum) is a perennial and currently distributed in the Lower Mainland, Fraser Valley, Gulf Islands, and central to southern Vancouver Island.

Giant hogweed has numerous small white flowers clusters in an umbrella-shaped head, with stout, hollow green stems covered in purple spots. Dark green leaves are coarsely toothed in 3 large segments with stiff underside hairs, and lower leaves can exceed 2.5 metres in length. Giant hogweed can grow up to 5 metres in height at maturity.

Giant hogweed is a highly competitive plant due to vigorous early-season growth, tolerance of full shade and seasonal flooding, as well as its ability to co-exist with other aggressive invasive plant species. Each plant can produce up to 100,000 winged seeds (typically 50,000) that remain viable in the soil for up to 15 years. Plants generally die after flowering.

Warning: Giant hogweed stem hairs and leaves contain a clear, highly toxic sap that, when in contact with the skin, can cause burns, blisters and scarring. WorkSafe BC has issued a Toxic Plant Warning for Giant Hogweed that requires workers to wear heavy, water-resistant gloves and water-resistant coveralls that completely covers skin while handling the plants. Eye protection is also recommended.

A few native and ornamental alternatives to plant instead of Giant hogweed include: Blue Elderberry; Ligularia; Rodgersia; Shieldleaf Rodgersia; and Wild Celery. Read more about these alternatives in the Grow Me Instead booklet for BC.

For more information:

• Best Practices for Management of Giant Hogweed in the Metro Vancouver Region
• National Fact Sheet on Giant Hogweed, by the Canadian Council on Invasive Species (CCIS)
• EDRR Fact Sheet on Giant Hogweed, by Randy Westbrooks, U.S. Geological Survey