7 poisonous plants to watch out for in Ontario

As an eager yet naive hiker, I must admit that I was ecstatic to be wandering alongside the Californian Coast, breathing in the fresh ocean air, exploring trails, and catching glimpses of the lush forest floor atop Carmel Valley. That was until I encountered any outdoor enthusiast’s sneakiest kryptonite: a poisonous plant.

Travelling back to Ontario with a nasty case of contact dermatitis was no fun. Now, I am more motivated than ever to learn about Ontario’s poisonous plants before returning to the trails.

Let’s discuss which culprits can cause harm to human health, how to identify them, and what to do if you come in contact with them.

1) Giant hogweed and 2) wild parsnip

Ontario is home to many poisonous plants. But giant hogweed and wild parsnip are particularly harmful to human health. “Both plants cause itchy and painful rashes,” says Vicki Simkovic, the coordinator for the Ontario Invasive Plant Council. “They can cause long-term issues like increased risk of melanoma and skin cancer,” she says.

If you suspect contact, cover the skin immediately and wash with cold, soapy water. “The chemical compound found in both these plants is phototoxic, meaning their sap only reacts negatively to the skin when exposed to UV light,” says Derissa Vincentini, the community science coordinator and GIS lead at the Invasive Species Centre. “Avoid sunlight for 48 hours and launder any exposed clothes immediately.”

Contact with giant hogweed and wild parsnip can lead to a rash similar to a second-degree burn. Simkovic recommends applying sunscreen and keeping the area cool to minimize harmful effects. “Warm temperatures and sweating can cause the pores to open and further absorb poisonous sap,” she says. Always visit a medical professional at the sign of blisters forming.

You’ll typically find the giant hogweed and wild parsnip growing in moist soil, in ditches, forest edges, meadows, and parks. “Both giant hogweed and wild parsnip overgrow, out-compete native plants, and cause soil erosion,” says Simkovic. “These plants do not contribute to local ecosystems or animal diets.”

How to get rid of them

Both giant hogweed and wild parsnip belong to the carrot family and can be confused with other plants like cow parsnip or Queen Anne’s lace. If you encounter them in your backyard, don’t pull them. Instead, contact a professional with the tools and outerwear to avoid spreading the invasive plants.

How to stop their spread

Staying alert and identifying these plants is the best way to avoid reactions. To prevent their spread, Vincentini recommends staying on trails to limit the number of seeds spread by shoes. “Keep a watchful eye on pets because sap from the giant hogweed and wild parsnip can blind pets,” she says. Report these invasive plants to EDDMapS, iNaturalist, or to your local municipality, which often has invasive reporting lines.

3) Pokeweed

In Canadian meadows and Southern Ontario landfills, pokeweed has a smooth, bright red stem, fleshy green leaves, and purplish berries. This plant can cause sickness in both livestock and people. If ingested, seek medical attention immediately, and do not make someone throw up—this will only make the infection worse.

4) Spotted water hemlock

Often mistaken for cow parsnip and commonly found near Ontario waterways, the spotted water hemlock has a long stem, an umbrella-shaped plant of smaller umbels, and individual white flowers with four to six petals. It is Ontario’s most poisonous weed; all parts of this plant can cause sickness and even death. If you come in contact with it, seek medical attention immediately and call the Ontario Poison Centre at 1-800-268-9017.

5) Poison ivy

Poison ivy is a plant that many cottagers are acquainted with. Its infamous leaflets of three make it highly identifiable. But don’t be fooled: while it is bright green in summer, it becomes reddish in fall. You may encounter this plant in both the open and in the deep woods. Poison ivy can cause a rash upon touch thanks to its oil, and even dead plants can cause a reaction.

If you encounter it, wash your skin with cold water and soap. Also, don’t forget to launder your clothes, scrub down your furry friends, and avoid scratching, which almost always leads to an infection.

6) Stinging nettle

Stinging nettle typically grows in the summer and fall and can get up to one metre in length. It has heart-shaped leaves, flowers that are pink and yellow, and the whole plant is covered in tiny hairs. Find it nestled in flood plains, old pastures, woodland, and along streams. While it has long been used as a herb, stinging nettle’s fine hairs can irritate the skin. Thankfully, the rash doesn’t typically last long, especially if you can wash the area immediately with cold water and soap. Remove any hairs from the skin and keep it clean.

7) Common moonseed

It may look like a grape, but common moonseed doesn’t taste like one and is toxic to humans. When comparing the two: moonseeds have a single crescent-shaped seed, whereas grape seeds are round. They grow across Canada. According to PictureThis’ Toxicity report, moonseed is dangerous to human health and can be deadly to animals because of its poison, the alkaloid dauricine. It’s safe to say that eating it is off the table. Otherwise, if you come into contact with it, wash your hands immediately with cold soap and water.