Giant hogweed is an aggressive invader that was first introduced to North America as a garden ornamental. It closely resembles our native plant cow parsnip, except the taller giant hogweed can grow up to 6-metres or more; while cow parsnip grows to no more than 2-meters.
* If you find Giant Hogweed, please Report it!
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.
Family: Apiaceae (Carrot).
Other Common Names: Giant Cow-parsnip, Hogweed
Description: Herbaceous perennial. Stems are hollow, ridged, green with purple spots to purple – red, may have stiff hairs present. When in flower, plants can grow to 6 meters tall. Flowers have small white flowers clustered in large umbrella-shaped head and up to 1.5meters across. Leaves are green and deeply incised (almost to leaf vein) and have 3 segments. Leaves can exceed 2.5 m in length.
Reproduction: Flowers are formed after 1-4 years of growth. Each flower head produces 100,000 seeds; which can persist in the soil for up to 15 years.
Legal Status: Weed Control Act, Community Charters Act, Listed under Bylaw 2347 in the Comox Valley Regional Districts’ Weed Control Regulation Bylaw
Agricultural: Can infest agricultural areas. Ecological: Strongly competitiveplant; dense stands of very, tall plants outcompete native species. Roots are shallow compared to mixed native communities, which may increase erosion risks in riparian areas.
Human: Sap which gets on skin causes hypersensitivity to sunlight; resulting in irritation, blistering and dermatitis which is re-aggravated with exposure to sunlight for several years. Scarring and blindness may result.
Habitat: Adapted to rich, damp soil and tolerates a wide range of light regimes. Grows on wet to moist disturbed sites at low elevations. Inhabits streams, wetlands, ditches, roads, right-of-ways, agricultural areas, wooded ravines, vacant lots, and other disturbed sites.
Distribution: Present in all Regional Districts within the Coastal ISC Service Area. Widespread in Nanaimo area, common in Comox Valley, Cowichan Valley and Strathcona. Limited in Alberni-Clayoquot, Capital, Sunshine Coast and Powell River. Most common in CDFmm and CWHxm but also reported in CWHvm and CWHvh.
Management Strategy: Use protective clothing and eyewear when handling all parts of this plant! Cut off flowers to prevent seed formation. Excavate plants, severing roots 8-12 cm below the soil surface. DO NOT COMPOST; dispose of all plant parts in strong garbage bags. Return to site to check for regrowth. Immature plants can be controlled by covering with black plastic or by mowing at 2 week intervals; 3-5 years of follow-up treatment may be required. Chemical controls can be effective, foliar applications are most effective in spring followed by a summer application on late appearing sprouts. Stem injections or cut stem and injections are effective after heavy sap flow in spring. No biological control agents are available.
For more information on how to manage Hogweed on your property and how we can help, visit our other page on Hogweed management.
Look-a-Likes, produced by the CoastalISC
Control Methods for Giant Hogweed in BC, produced by the CoastalISC