Giant Hogweed

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Giant Hogweed
(Heracleum mantegazzianum)

Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

About Giant Hogweed: An Invasive Plant in Maryland

Life cycle/information: Giant hogweed (Heracleum mantegazzianum) is a herbaceous perennial plant native to the Caucasus Mountains of western Asia. It has been cultivated in the United States, primarily as a curiosity, since the early twentieth century. In natural areas, it outcompetes native plants and poses a threat to human health. It contains a chemical, furocoumarin, which can cause severe irritation, blistering, and burns to human skin exposed to the plant sap and then sunlight. Giant hogweed is on the federal noxious weeds list. As of 2018, it has been found and controlled in several Maryland counties.

Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Growth habit: Giant hogweed grows 10-20 feet tall and has deeply lobed leaves up to 5 feet wide. The stem is 2 to 4 inches in diameter, hollow, and covered with purple blotches and sturdy bristles. The leaves are alternate along the stem. Tiny white florets are produced in a large, flat-topped inflorescence up to 2.5 feet in diameter in mid-May-July. The plants die back to the roots in late summer.

Giant hogweed stem. Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Common cow-parsnip, poison hemlock, elderberry, Queen Anne’s lace, and angelica are plants that look somewhat similar and are commonly mistaken as giant hogweed.

Giant hogweed leaf. Photo: Thomas B. Denholm, New Jersey Department of Agriculture, Bugwood.org

Reproduction: Giant hogweed produces ⅜ inch flattened oval dry fruits. The plants spread by seeds.

Conditions that favor growth: Moist, rich soils of floodplains, streambanks, and roadsides.                                                                                   

Dealing With Giant Hogweed

Do not cultivate or handle giant hogweed. If you think you see this plant, do not touch it. Take clear digital photos of the plant (flower, stem, foliage) and send them to the University of Maryland Extension Home & Garden Information Center’s Ask an Expert service for identification. Suspected findings of giant hogweed will be reported to the Maryland Department of Agriculture Plant Protection Division.

References and Resources

• Center for Invasive Species and Ecosystem Health (Invasive.org), Giant Hogweed.
• Kaufman, Sylvan Ramsey & Wallace Kaufman. 2007. Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species.
• Maryland Invasive Species Council, Invader of the Month, Giant Hogweed, April 2003.
• New York State, Department of Environmental Conservation, Giant Hogweed Identification.

Compiled by Christa Carignan, reviewed by Debra Ricigliano, University of Maryland Extension, 10/2018.