Giant hogweed is a tall (up to 15-20 ft. [4.6-6.1 m]), herbaceous, biennial plant that invades disturbed areas across both the Northeast and Pacific Northwestern United States. Giant hogweed is designated as a Federal Noxious Weed, because it produces sap that causes skin sensitivity to UV radiation and leads to blistering and severe burns. The large stem is hollow and usually marked with purple blotches. The leaves are deeply lobed, sharply pointed, and up to 5 ft. (1.5 m) wide. Flowering occurs in late spring to early summer. The white flowers are on a large umbrella-shaped head at that can be up to 2.5 ft. (0.8 m) in diameter. Giant hogweed can invade a variety of habitats but prefers moist, disturbed soils such as riverbanks, ditches and railroad right-of-ways.
Because of its size and rapid growth, giant hogweed is an aggressive competitor capable of displacing native plants. It dies back during the winter months, leaving bare ground open to erosion on riverbanks and steep slopes. The sap of giant hogweed makes human skin sensitive to ultraviolet light, resulting in severe burns and blisters. Contact with the eyes can cause permanent blindness.
Giant hogweed is native to Europe and Asia. It was first introduced into the United States in 1917 for ornamental purposes.
Forests, forest edges, meadows, fields, disturbed areas
Giant hogweed sprouts in early spring and flowers early July. This perennial plant dies back after flowering, leaving tall dead stalks. It forms perenating buds which lie dormant through winter until the next growing season. It reproduces by seed dispersal only, not vegetatively. Each flower head contains approximately 1500 seeds, which can remain viable for up to ten years.
Giant Hogweed next to building, UGA1151035, Terry English, USDA APHIS PPQ, CC 3.0
Giant Hogweed flower clusters, 1460061, Donna R. Ellis, University of Connecticut, CC 3.0
Giant Hogweed, 5474254, Rob Routledge, Sault College, CC 3.0
American Cow Parsnip, 5382426, William M. Ciesla, Forest Health Management International, CC Non-com 3.0
Vermont Chapter of The Nature Conservancy