By Donna Monnes

What is worse than Poison Ivy? It’s called Giant Hogweed (Heracleum mantegazzianum) and you don’t want to touch this plant! It is on the Federal Noxious Weed List, and it’s here in Connecticut.

Giant Hogweed, a native to the Caucus regions of central Asia, was introduced into Europe in the 1800s. A tall and majestic plant, it was brought to the United States in the early 1900s for use in ornamental gardens in New York, where it escaped from cultivation and established itself in the wild. It’s not picky where it grows. It likes full sun and shade and flourishes in moist soils and along woodland edges, ditches, and stream banks. As with other invasive species, Giant Hogweed invades natural areas and displaces native (local) plants, upsetting the ecological balance of important natural habitats. It has been in Connecticut since 2001 and you can find it in 25 Connecticut towns.

Giant Hogweed is a monocarpic (it flowers, seeds, and dies back), herbaceous (non-woody stemmed), biennial or perennial plant with deeply lobed and jagged leaves. It is a member of the carrot or parsley family (Apiaceae) and can grow up to 15 feet tall. The flowers are numerous, small and white, and clustered into large flat-topped umbels. The stems are green with purple blotches and course white hairs, and are hollow, measuring up to 2 to 4 inches in diameter. Just one plant can produce 20,000 seeds!

The clear sap from the plant can be dangerous, causing large painful burning blisters within 24 to 48 hours of contact with the skin when also exposed to the sun. It can also cause long term or permanent scarring that is sensitive to sunlight. Temporary (sometimes permanent) blindness can result if the sap comes in contact with the eye. Furocoumarins that are in the sap are activated when exposed to ultraviolet light in a reaction known as Phytophotodermatitis (phyto = plant, photo = light and dermatitis = skin rash). If you come into contact with the sap, be sure to wash the affected area thoroughly with soap and COLD water as soon as possible and keep the exposed area away from sunlight for 48 hours. See a doctor if any sign of reaction sets in.

A relative of the Giant Hogweed, Cow’s Parsnip, is a native species found throughout most of the Pacific Northwest. Cow’s parsnip does have similar lobed leaves and is 5’ tall and wide, but they will not be as deeply lobed as the Giant Hogweed. The sap will also cause a rash similar to that of Giant Hogweed, but not as severe. Wild parsnip and other plants in the carrot family have similar yellow umbrella shaped flowers.

Remember that exposure to the Giant Hogweed sap and sunlight will result in a skin rash in 24 to 48 hours after contact. So, when out in the woods and fields (just like with Poison Ivy) – please don’t touch any Giant Hogweed!

This article drew on information from the University of Illinois and University of Connecticut Extension Centers, and the Connecticut Invasive Plant Working Group. For more information go to:

Brochure: Giant Hogweed – An attractive but dangerous noxious weed

Poster: Wanted: Giant Hogweed