Canadians are flocking to the outdoors in increasing numbers. More than half a million Canadian households packed up tents and went camping for the first time in 2022, according to the 2023 North American Camping and Outdoor Hospitality Report, commissioned by Kampgrounds of America (KOA). They are also hiking, mountain biking, running and kayaking in the summertime.

But there is a need for caution as Canada has a bounty of poisonous plants. While they aren’t typically lethal to humans, they can still cause illness or harm if touched or ingested.

Mhairi MacFarlane, director of science and stewardship, Ontario Region, for the Nature Conservancy of Canada, says the NCC, Canada’s largest land conservation organization, is working to remove harmful species from its nature reserves in Ontario.

Some of Canada’s most poisonous plants

Dr. Francois Tardif, a professor in the Department of Plant Agriculture at the University of Guelph, says it’s tough to rank poisonous plants in this country because they are all toxic in different ways. However, both Tardif and the NCC did reference the first one on our list as particularly dangerous.

Giant hogweed

A conservation biologist with the NCC told the CBC that the giant hogweed is one of the most dangerous plants in Canada, is increasingly invasive and warned Canadians to be on the watch out for it.

The giant hogweed, found in Ontario, B.C., Quebec and the Maritimes, has chemicals called furanocoumarins, which can cause blisters and burns if the plant’s sap contacts human skin in combination with sunlight.

“It’s a member of the carrot family (like water hemlock) that is quite a spectacular plant,” says Dr.Tardif, who researches herbicide resistance in weeds. “Introduced as an ornamental to Western Europe, then to North America, it has become both an environmental issue as an invasive plant and a public health issue due to its toxicity.

“The furanocoumarins are molecules that are contained in its sap and will get into the skin cells after contact. Once in the cells, these compounds bind to the DNA and react with UV rays to trigger programmed cell death. The result is equivalent to a chemical burn with reddening, blisters, skin hyperpigmentation – basically, light-induced dermatitis.” It is also a poisonous plant for dogs since it causes skin irritation, blistering, and burns.

Poison Ivy

This poison ivy plant is quite common near trails, at the margin of wooded areas and other shaded spots.

Poison ivy is a low-growing vine plant, sometimes a climber. It contains non-volatile oils called urushiols. These will get on the skin if you brush by a plant, then seep into cells and trigger an allergic reaction, resulting in painful dermatitis – skin rashes, blisters, severe itching. All parts of poison ivy are toxic.

Dr.Tardif says he heard of a case in which an individual’s dogs played in a ravine, got the toxin on their fur, brought it back into the house and onto the sofa, where the unsuspecting owner got it on their skin.

“There are also, equally or more toxic, poison oak and poison sumac that can be seen in Canada, although more rarely in my experience,” he adds.

Water hemlock

This plant is considered the most poisonous of all Ontario perennial weeds since it contains a toxic compound called cicutoxin. Ingesting even a small amount can lead to seizures, respiratory failure and death.

“It contains toxins that paralyze the nervous system and stop breathing,” Dr. Tardif says. “It is toxic to livestock – grazing animals have died consuming it. On the positive side, you have to go out of your way to find it as it is found in small populations or individual plants in wet spots (near creeks, swamps, ditches). My concern is that people interested in foraging wild plants may come across it and get it mixed-up with other plants of the carrot family.

“I have also read that it can sometimes be used in floral arrangements as the flowers are interesting looking and similar to those of wild carrots. This would be non-advisable as the sap is also toxic. How toxic? Its other names include cowbane, poison parsnip, children’s bane and death-of-man, among others.”

Wild parsnip

Abundant in eastern Ontario on roadsides and pasture meadows, this one has the same toxic chemicals as giant hogweed, Dr. Tardif says. It’s more tolerant of dry conditions.

Canada Yew

The seeds and leaves of these plants contain a poisonous compound called taxine. If ingested in any way, this can lead to dizziness, vomiting, tremors and even cardiac arrest.

Jimsonweed

This plant is sometimes found in farmers’ fields and is also grown as a spectacular ornamental. One of its alternate names is the devil’s trumpet.

“It is a member of the nightshade family, which includes many very toxic plants,” Dr. Tardif says. “Interestingly, this family also comprises economically important food plants such as potatoes, tomatoes, eggplants and peppers. Jimsonweed produces many different toxins that can cause hallucination, impairment of the nervous system, paralysis and all sorts of nasty stuff. All parts are toxic and there have been reports of intentional seed consumption, presumably in a search for hallucinogenic effects, resulting in overdosing and death.”

What can you do to protect yourself?

Defending yourself against these toxic plants depends somewhat on the species and situation, but some basic strategies include:

• Be aware. Use multiple sources to confirm the identity of a plant you are unsure of. “We encourage people to make use of identification guides and apps like iNaturalist to identify the plants and animals around you when you are out in nature,” MacFarlane says. “It is always best to leave things as you find them, as this leaves resources available for animals, birds and insects to eat, nest with or shelter in over winter.”
• Get rid of them. On small infestations, cutting or pulling the roots of lawn weeds may be sufficient, Dr. Tardif says. But with larger invasions, herbicides may have to be used. Tarping with plastic or heavy mulching after mowing may work as well, he adds.
• Wear protective clothing. Especially when it comes to plants that are poisonous to the touch, wearing rubber boots and gloves, long pants and sleeves, and eye and face protection can help protect you.
• Use barrier creams. Lotions containing bentoquatum offer some protection against contact with such noxious plants as poison ivy, poison oak and poison sumac.
• Scrub down any equipment, garden tools or camping gear with rubbing alcohol or soap and water.

If you have come into contact with a poisonous plant, wash your clothing and skin immediately, and clean any clothes you have been wearing. Wet compresses, calamine lotion, oatmeal baths, antihistamines or hydrocortisone cream can ease symptoms such as itching and rashes. If you have a severe allergic reaction or difficulty breathing, get medical help right away.

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