invasive giant hogweed in flower

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

Updated: June 3, 2021
By Christa Carignan

About giant hogweed

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.

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.

Common cow-parsnippoison hemlockelderberryQueen Anne’s lace, and angelica are plants that look somewhat similar and are commonly mistaken as giant hogweed.

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.

Managing 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 Extension service for identification. Suspected findings of giant hogweed will be reported to the Maryland Department of Agriculture Plant Protection Division.

Giant hogweed flower

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

Giant hogweed stem

Photo: Rob Routledge, Sault College, Bugwood.org

 

Giant hogweed leaf

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

Additional resources

Giant Hogweed | Center for Invasive Species and Ecosystem Health (Invasive.org)

Giant Hogweed | Maryland Invasive Species Council, Invader of the Month, April 2003

Giant Hogweed Identification | New York State, Department of Environmental Conservation