invasive giant hogweed in flower

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

Updated: May 11, 2022
By Christa Carignan

About giant hogweed

Giant hogweed (Heracleum mantegazzianum) is a perennial herbaceous invasive plant that poses a severe human health risk. Originally from the Caucasus Mountains of western Asia, this plant has been cultivated in the United States, primarily as a curiosity, since the early twentieth century. Giant hogweed can grow up to 20 feet tall and has large umbrella-like flowers that bloom from mid-May to July. The sap of the plant can cause severe irritation, blistering, and burns to human skin when exposed to sunlight. Giant hogweed is on the federal noxious weeds list, which is intended to limit its spread. Giant hogweed has been found and controlled in a few Maryland counties, but it is not common. There are several look-alike plants that are often mistaken for giant hogweed. Key characteristics for accurate identification of this plant are provided below.

Photos of giant hogweed

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

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 are spread by seeds.

Conditions that favor growth

Moist, rich soils of floodplains, streambanks, and roadsides.

Managing giant hogweed in Maryland

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. We will report positive findings of giant hogweed to the Maryland Department of Agriculture Plant Protection Division.

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

Still have a question? Contact us at Ask Extension.