Invasive Plants, Pacific Northwest
Giant Hogweed grows all over the Pacific Northwest with greater concentrations in some areas like Vancouver Island. It will grow in a variety of habitats but is fond of areas adjacent to streams, creeks, roads or right of ways. It is frequently found in areas that are quite wet. It is a perennial member of the parsley family and is native to Asia.
It closely resembles our native plant, cow parsnip, except the taller Giant Hogweed grows up to 6 meters or more. It was first introduced to North America as a garden curiosity. It is well established as an invasive plant on BC coast, including Vancouver Island, the Gulf Islands and the lower mainland.
Aside from its immense size, it is also distinguished by it’s stout, dark reddish stem that can grow up to 10 cm in diameter. Leaves can grow up to 1.5 meters across. Each leaflet is deeply grooved or divided. Both stems and stalks are hollow and produce coarse hairs around a blister like pustule.
Each year tuberous root stalks form long lived buds. In summer small,white flowers form together to make up an umbrella shaped head that can attain a diameter up to 1 meter. Giant Hogweed reproduces through seed and perennial buds. The seeds remain viable for up to 7 years.
The greatest concern from this plant is human health. The blister like pustules on stems and stalks exude a clear watery sap that sensitizes skin to ultraviolet radiation. Sunlight on the affected areas can result in severe burns that usually result in blistering and painful dermatitis. Blisters often result in purplish to blackened scars. Very nasty.
Giant Hogweed’s fast growth and large size allows it to readily occupy and crowd out native vegetation. In riparian areas it forms a dense canopy, driving out native species and causing stream bank erosion.