Return of the giant hogweed

Moira Baird
Published on May 21, 2010
Above, the giant hogweed flowers from July to August. Below, the giant hogweed can grow up to 15 feet in height in the warmer climates of B.C. Top photo courtesy of Isabelle Simard, MDDEP; bottom photo courtesy of Invasive Plant Council of B.C.

Last year, the giant hogweed was a novel, troublesome pest found along a portion of the Virginia River trail in the east end of St. John's.
This year, it's the poster plant for invasive species in the province and right across the country.
Giant hogweed can grow taller than the average person, and the clear sap from its leaves and stems can burn skin, producing blisters and scars.
"Giant hogweed is not only a threat to biodiversity, it's a human health hazard," said Todd Boland, research horticulturist with Memorial University's Botanical Garden.
On Saturday - international day of biodiversity - Boland will explain the perils of allowing the giant hogweed to gain a foothold in the province during a 2 p.m. lecture at the Botanical Garden.
Boland is the Newfoundland representative on the Invasive Alien Species national working group. His lecture will kick off a nationwide series of similar presentations.
Giant hogweed is similar in appearance to cow parsnip, which is native to North America and is found mostly along roadsides on the Northern Peninsula.
"It's not easy to tell them apart,"?said Boland.
The leaves of a giant hogweed can grow several feet in length, and are pointier and more deeply serrated than those of cow parsnip. As well, the stem hairs are bristly rather than soft.
An impressive sight, giant hogweed flowers from June to August, featuring large, umbrella-shaped heads consisting of many small, white flowers.
The sap from cow parsnip is also phytotoxic, but it will only cause a rash. Giant hogweed sap is much more toxic.
Boland said it can take up to five years of diligent work to eradicate giant hogweed.
"One plant can produce thousands of seeds. The seeds can survive in the ground for a couple of years before they germinate.
"The big problem with that plant is it usually grows around rivers. It likes wet areas, and the seeds fall into the Virginia River and they'll just flow on down the river."
Travelling seeds can be a problem.
"There's instances where seeds have turned up elsewhere 10 kilometres downstream from where the darn plant was.
"So, it has potential to become quite a pest, if it's not nipped in the bud, pardon the pun."
Following an August 2009 Telegram story, the Botanical Garden received several calls, but the reported plants turned out to be angelica.
"It's an edible plant and there's absolutely no reaction to it whatsoever."
And unlike the giant hogweed, its stem is smooth.
Boland recommends not touching any suspected giant hogweeds - just send photos by
e-mail to so he can identify the plant.
The goal of the invasive plant campaign is to prevent giant hogweed from becoming the kind of major pest it is in Europe.
It arrived there in 1817 from the Caucuses and central Asia as an ornamental garden plant.
"It's a big, imposing plant."
A century later, giant hogweed arrived in North America.
"How it got to Newfoundland, God only knows. Presumably, it came in infected soil."
Boland said giant hogweed is a serious problem in British Columbia, where it can grow up to 15 feet tall along the coast, and in southern Ontario.
There's a small population in Quebec, and only one known location in both Nova Scotia (in Cape Breton) and Newfoundland.
Here, the plant can grow to six to eight feet tall.
So far, it doesn't appear to be present in New Brunswick, P.E.I. or the Prairies, but it is on their watch lists.
It can tolerate climate zones of five - such as Newfoundland - or warmer.
Invasive plants out-compete indigenous plants and take over an area. Because giant hogweed's deciduous leaves can span several feet, it shades neighbouring plants, which then die off.
In B.C., for instance, all the bare ground beneath the giant hogweed has led to soil erosion and the silting of streams.
"That could become an issue here because it's growing along the Virginia River," Boland said.