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Giant Hogweed





Giant hogweed favors rich, moist soils.  It is shade tolerant and can withstand seasonal flooding and is commonly found along stream banks, roadsides, open woodlands, or other damp, disturbed areas.  Once giant hogweed is present in riparian landscapes, it is capable of spreading seed long distances.  Seeds can drop into nearby channels and utilize flowing water as a vector for traveling great distances.

  Giant hogweed currently has a limited distribution in the CRISP Region. To date, infestations are fairly small and have been managed promptly by the New York State Department of Environmental Conservation Giant Hogweed Control Program and CRISP. Small populations of giant hogweed have been identified in Otsego, Sullivan and Ulster Counties (Figure 2, Table 1, Appendix B). If you believe you have giant hogweed on your property or you have seen it in the region, alert CRISP by calling 845-586-2611, ext. 103.


Giant hogweed (Heracleum mantegazzianum) is an invasive plant species native to the Caucasus region of Eurasia; its massive size and showy inflorescence led to its deliberate introduction into the United States as an ornamental species for arboreta and Victorian gardens in the early 1900s.  Soon after its introduction, giant hogweed escaped from cultivation and began growing in the wild.  Its ability to crowd out native species, as well as its threat to human health, led the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service to list giant hogweed as a Federal noxious weed.


Giant hogweed is a member of the carrot and parsley family (Apiaceae).  Plants occur as either biennial or perennial herbs growing from a large taproot. Taproots provide resource reserves and enable plants to survive for multiple growing seasons.  It may take three to four years for a plant to produce a single flower.  Rosettes of leaves will come up each spring until the taproot has built up enough to support a tall flowering stalk.  Bolting occurs starting in mid-June with flowers going to seed in late July to early August. Usually, after flowering and setting seed, the entire plant will die, but cases have been reported of plants as old as 25 years.   

Each plant produces an average of 20,000 to 100,000 seeds.  Seeds may be transported by wind or water, but most remain close to the parent plant, with most seeds occurring within the top two inches of soil.  Seed viability may persist for more than five years. Vectors for spread of seed in the Catskill Region include mowing along transportation corridors, movement by streams, transport of contaminated soil, and intentional sharing of seeds or seedlings.

Favorable soil, moisture, and light conditions in the Catskills offer suitable habitat for giant hogweed.  The large second homeowner population within the Catskills is also of concern, as part-time residents may bring seed into the region from other parts of the state, unaware of the consequences of introduction.

Human Impact

Giant hogweed is hazardous to human health due to toxic compounds in its sap (furocoumarins) that cause photosensitization.   The sap, a clear watery substance, can exist in all parts of a giant hogweed plant— on the stem, foliage, flower and fruit. Contact with the sap followed by exposure to sunlight causes a serious skin reaction known as phytophotodermatitis.  Phytophotodermatitis is characterized by hypersensitivity to ultraviolet light; reactions caused by contact with giant hogweed sap may include painful, burning blisters that appear within 24 to 48 hours of contact or painless red spots that develop into persistent purple to brown- colored scarring.  When eyes are exposed to giant hogweed sap, blindness may result.


If an individual does come into contact with the sap of a giant hogweed plant, the area should be immediately washed with cool, soapy water.  In order to minimize phytophotodermatitis, the affected area should be covered and exposure to ultraviolet light should be avoided for 48 hours following contact. 

Biological Impact

Biological traits such as prolific seed production and rapid growth enable giant hogweed to readily establish and out-compete native vegetation.  Giant hogweed’s tall stature and huge leaves produce shade, choking out nearby native plants through sunlight deprivation.  The inhospitable shade generated by giant hogweed plants leads to the presence of bare soil beneath hogweed plants. This is particularly problematic when giant hogweed colonizes slopes or stream banks. In addition to bare ground generated by shade produced by giant hogweed’s large leaves, giant hogweed has a fairly shallow rooting depth, making it less effective than native plants at holding soil in place.  Giant hogweed infestations are therefore linked to accelerated rates of soil erosion, especially on sloping and/or riparian landscapes.


Plants may reach heights of up to 15 feet, and can be distinguished by their large, showy, white umbel inflorescence; thick hollow stem covered in purple splotches and coarse white hair; and large, lobed, deeply incised compound leaves.  Although they typically sprout in the early spring, giant hogweed plants are most easily identified when they are flowering— around June-July.

1. White flowers with 50-150 flower rays clustered into an umbrella shaped flower cluster up to 2.5 feet across


2. Between 7 and 14 feet tall (depending upon growth stage and if mowed or cut)


3. Huge leaves, incised and deeply lobed up to 5 feet across


4. Stems are green with extensive purple splotches and prominent coarse white hairs. Stems are also hollow, ridged, 2-4 inches in diameter, and have a thick circle of hairs at base of leaf stalk


5. Seeds are dry, flattened, and oval. Approximately 3/8 inch long and tan with brown lines (oil tubes) extending 3/4 of the seed length that widen at ends


Page Sources & Useful Links

New York State Department of Environmental Conservation Giant Hogweed Information:

United States Department of Agriculture National Invasive Species Information Center:

New York State Department of Environmental Conservation Giant Hogweed Distribution Map: Giant Hogweed Information and Photos: