Giant hogweed is a tropical-looking perennial herb in the carrot family that was introduced to North America from southwest Asia. The plant is noted for its huge umbrella-shaped clusters of flowers up a meter across, growing atop stems 5m or more in height. Giant hogweed looks very similar to the smaller growing H. maximum, our native cow parsnip.
How does it spread?
Giant hogweed reproduces through seeds, which can be spread by animals, surface run-off, water and wind currents, rain, machinery, vehicles and through intentional plantings. A mature plant can produce 50,000 -120,000 seeds that can remain viable in the soil for many years.
Where would I find it?
Giant hogweed prefers rich, damp to wet soil and a variety of exposures. It can be found growing along river and stream banks, roadsides, right-of-ways, ditch-lines and in vacant lots, riparian and agriculture areas, wooded ravines, old fields, open woodlands and other disturbed sites.
What problems does it cause?
Infestations increase the risk of erosion, as the leaves over-shade and kill native vegetation, leaving the soil unprotected after winter dieback. The plant is photodermotoxic – its leaves and stems contain a clear, watery, highly toxic sap that once activated by solar radiation, can cause hypersensitivity to sunlight and result in severe skin dermatitis, burns, blisters, and scarring. Contact with the eyes can cause blindness.