Stinging nettle

Editor’s note: The following is meant as general information only and should not be used as a substitute for professional medical advice.

Absentmindedly, I had left my gardening gloves at home. A few nights later, an insidious itch crept down my neck and back. Soon after, red, oozing blisters broke out and spread across my body. The walk-in clinic doctor diagnosed a bad case of poison ivy. The effect was a bit of a horror show, at least until the medication took effect.

Even experienced gardeners sometimes fall prey to plants that can cause pain, misery and, although rare, even death. Some are native species; others, non-native. Each year, people, often children, and sometimes pets are poisoned or otherwise harmed from toxic berries, bulbs, leaves and other plant parts.

Of course, most plants are beneficial and perfectly benign, but hazardous plants, though much fewer in number, are found everywhere. They grow on country properties or in woods near swamps and streams. Sometimes, they are found on abandoned lots in cities and suburbs. They can even be found in our yards and homes. Readers, take heed: wear gloves, don’t eat strange berries, educate your kids and remove hazardous plants that are a risk to you and your pets. Here are 10 common ones to avoid.

1. Stinging Nettle (Urtica dioica)

This quick-growing perennial is often found in orchards, untended pastures, farmyards, ditches and waste places. I discovered it while gardening in an old farmyard. Contact causes a painful sting from the tiny, needle-like hairs on the stem, leaf and flower. This is followed by prolonged numbness and itching that may last a few minutes or even a few days if there is repeat contact. While rarely serious, the sting can be nasty.

Giant Hogweed

2. Giant Hogweed (Heracleum mantegazzianum)

This enormous plant, also called giant cow parsnip, is originally native to Asia. It was introduced to North America as an ornamental garden plant with no known diseases or insect pests. It has become an invasive species that can grow to more than 16’ (5m) tall. It has white, umbrella-shaped flowers and large leaves that can span 3’ (1m) across. The plant is often found along footpaths and riverbanks, and sometimes finds its way into a backyard garden.

The sap from this plant can cause severe, painful burns and can also make your skin sensitive to sunlight. If the sap comes into contact with someone’s eyes, it can lead to temporary or permanent blindness.


3. Ragweed (Ambrosia spp.)

This is considered the number one cause of hay fever, in part because of its abundance and the fact that it flowers all summer long. You find it along driveways, roads, sidewalks and cultivated fields. It tends to grow where soil has been disturbed (another argument for mulching).

While there are dozens of varieties, the two that are mainly responsible for the sneezing, runny nose and itchy eyes, mouth and throat are common ragweed (A. artemisiifolia) and giant ragweed (A. trifida). Common ragweed grows to about 5’ (1.5m). It has long, deeply toothed divisions in each leaf, and spikes of small, numerous, greenish-yellow florets. Giant ragweed grows as tall as 14’ (4m). Both varieties begin flowering in June and release their pollen in July. Only frost will kill this plant, so the pollen continues until then. It thrives in hot, dry summer weather. Those who suffer from a ragweed allergy are best to avoid the outdoors during the middle of the day when pollen counts tend to be the highest.

Climbing Nightshade

4. Climbing Nightshade (Solanum dulcamara)

Also known as bittersweet, it’s native to Europe but has become a weed in North America. It is both a climbing vine and an erect herb. All parts of the plant are poisonous, but it is often the berries that are mistaken for edible fruit. Consumption brings on intense thirst, nausea, hallucinations, fever and high blood pressure. Its white or purple flowers resemble those of the potato or tomato, which are related. The plant flourishes in dark, shady spots, producing pointed, oval-shaped leaves and tubular flowers.

White snakeroot

5. White Snakeroot (Eupatorium rugosum)

This tall native North American plant, with its showy clusters of small, bright-white flowers, is easy to spot growing in fields, woods, thickets, lake edges, waste places and other shady areas. It prefers wet soil.

The leaves and stems of the plant contain an extremely dangerous poison called tremetol. When animals eat it, they develop a condition called the trembles that may cause death. The meat and milk of such animals can contain tremetol at levels toxic to humans. Fortunately, this condition is rare nowadays because of modern-day farming practices.


6. Rhubarb (Rheum rhabarbarum)

A spring ritual for many gardeners is to pick fresh rhubarb from the garden and use the stalks to make tasty sauces, pies and crumbles; however, the large, coarse leaves are toxic. Consuming them can cause nausea, vomiting, burning in the mouth and throat, abdominal cramping and diarrhea.


7. Burdock (Arctium spp.)

This weed’s purple, rounded flower heads have hooks that attach to clothing, hair and animal fur, which can result in several hours of serious grooming if you happen to be walking a shaggy dog. When pets try to remove the prickly seeds themselves, they can irritate their skin; if they consume them while doing so, it can cause intestinal hairballs. Interestingly, burdocks were the source of inspiration for Velcro, the fabric fastener.


8. Buttercup (Ranunculus spp.)

A favorite childhood game was to press a wild yellow buttercup to the skin just under the chin to test if you liked butter. A slight redness was supposed to be the sign of a butter lover. In reality, both buttercups, as well as the popular garden vine clematis (also part of the buttercup family), contain a severe skin irritant called glycoside. Physical contact with the leaves and flowers can cause irritation and blistering of the skin. Consumption, which is usually deterred by their strong, unpleasant flavor, can cause intense burning of the mouth and digestive tract. Gardeners should wear gloves when weeding buttercups or when planting clematis.


9. Jack-in-the-Pulpit (Arisaema triphyllum)

This is an unusual-looking wildflower, with a green and white hood shaped like a pulpit. It produces clusters of red berries, which can be especially attractive to children. If the berries are eaten, symptoms include a painful burning in the mouth and throat, swelling and choking. If large amounts are consumed, convulsions, coma and death can result.

Poison Ivy

10. Poison Ivy (Toxicodendron radicans)

This woody plant causes countless cases of contact dermatitis in humans. “Leaves of three, let them be” is the common warning. The toxin, called urushiol, is easily spread, especially if you scratch the affected areas or come into contact with previously contaminated clothing. Fortunately, the rash does not spread from one person to another. Poison ivy is most dangerous when burned, as the poison rises in tiny drops in the smoke and ashes. Breathing this smoke can cause severe damage to the lungs and even death.

These are just a few of the plants to heed while enjoying the gardening season.

Text and photos by Julianne Labreche

Julianne Labreche is a freelance writer and gardening enthusiast who volunteers with Master Gardeners of Ottawa-Carleton.

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