(NEXSTAR) — The definition of a weed is relatively vague — a plant growing where you don’t want it, experts explain — but some earn an extra adjective to describe them: noxious.
That term has a federal definition, thanks to the Plant Protection Act: “any plant or plant product that can directly or indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, poultry, or other interests of agriculture, irrigation, navigation, the natural resources of the United States, the public health, or the environment.”
One such massive, noxious weed may be growing in your yard, waiting to burn you if you try to remove it too quickly.
Heracleum mantegazzianum, better known as giant hogweed, has been present in the U.S. for more than a century, according to the U.S. Department of Agriculture’s National Invasive Species Information Center.
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Native to parts of Asia, researchers believe hogweed may have been brought to the U.S. as an ornamental garden option “because of its extremely large size and impressive flower.” It’s also possible its seeds, common in Middle Eastern cuisine, were among spice imports.
Nonetheless, the giant hogweed has found its way around the country. The plant has been positively identified in several states, including Connecticut, Illinois, Indiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Ohio, Oregon, Pennsylvania, Vermont, Virginia, Washington, and Wisconsin.
The perennial plant lives up to its name, reaching heights of 20 feet with massive umbrella-like flowers that bloom between May and July. The flowers, which grow in clusters, can reach diameters of 2.5 feet, according to the Washington State Noxious Weed Control Board. Hogweed stems and stalks, reaching up to 4 inches in diameter, have purplish-red blotches and stiff hairs. The leaves have toothed edges and can grow to 5 feet wide.
You can see photos of the stem, leaf and flower of a giant hogweed plant in the slideshow below.
Pennsylvania Department of Agriculture agent Michael Zeller shows a section of a stem from a giant hogweed plant cut down on a farm in McKean, Pa., Erie County, on Wednesday, July 9, 2003. Hogweed can be dangerous to people. Its sap causes a change in human skin, effectively making it a capacitor for the sun’s energy. Exposure to sunlight causes blisters. (AP Photo/Keith Srakocic)
Pennsylvania Department of Agriculture agent Michael Zeller shows off the leaf of a giant hogweed plant in McKean, Pennsylvania, on Wednesday, July 9, 2003. (AP Photo/Keith Srakocic)
BOLTON, UNITED KINGDOM- JUNE 24: Giant Hogweed plants grow on the banks of the River Irwell on June 24, 2025 in Bolton, United Kingdom. Giant hogweed is an invasive plant in the United Kingdom and introduced to Britain as an ornamental plant in the 19th century. (Photo by Christopher Furlong/Getty Images)
Hogweed is often found in moist areas, like along streams and rivers, where there is also shade. The massive plant is capable of causing soil erosion in these areas, which can give way for the seeds to be dispersed downstream to other areas, the Wisconsin Department of Natural Resources explains.
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It’s not unlike cow parsnip, a plant native to the U.S. Cow parsnip can often appear tall, as seen in the photo below, with heads of white flowers and wide leaves. There are some notable differences between cow parsnip and giant hogweed, however.
A 2008 photo shows a remaining patch of original prairie with cow parsnip in the foreground near Steptoe Butte in Whitman County in the Palouse, Washington. (Wolfgang Kaehler/LightRocket via Getty Images)
The New York Department of Environmental Conservation points to its size, for starters: Cow parsnip can reach roughly 6 feet in height, with flowers that are about a foot in diameter and leaves reaching 2 feet wide. That’s all about half of the size that hogweed can reach. Officials also say cow parsnip’s stems do not have the purple blotches found on hogweed.
Despite their differences, both plants are capable of irritating your skin. Sap from cow parsnip leaves and stems can give you a “blistery rash” if you have sensitive skin, officials in Maine explain.
Giant hogweed sap, found on all parts of the plant, can lead to severe burns in as little as a day, Nexstar’s WIVB reports. If you have sap on your skin and are in the sun, you can develop phytophotodermatitis, a skin condition brought on by chemicals found in certain plants and fruits, like citrus.
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“The sap interferes with the skin’s natural ability to protect itself from sunlight, resulting in severe burning and blistering,” according to an article from the University of Maryland Extension. “If sap goes into the eyes, it can cause temporary or permanent blindness.”
Phytophotodermatitis can appear like sunburn on your skin, the Mayo Clinic explains, and develop itchy patches like eczema. The condition can last for several months, with treatment limited to “self-care measures, such as soothing the affected skin with a cool, wet cloth.”
If you come in contact with giant hogweed sap, Supervising Park Ranger Chuck Bartlett of Erie County, New York, recommends washing your skin with soap and water “as soon as absolutely possible” while avoiding sunlight.
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Managing hogweed in your yard or on your property can vary based on the size of the plant. As seedlings or young plants, Washington state officials say giant hogweed can be dug up or hand-pulled, as long as you’re wearing protective gear to avoid contact with the sap. You can also cut back larger plants before digging them up, bagging the plant and its flowers for disposal.
You may also require a herbicide treatment, which could require assistance from an expert, Minnesota officials explain.
If you live in a state that has not yet confirmed the presence of hogweed and believe you have spotted the noxious weed, you may want to document the sighting and report it to agriculture or wildlife officials before removing it.
