Some Airdrie residents have spotted a striking, exotic-looking flower blooming in disturbed areas this summer. But despite its appearance, black henbane is a toxic invasive species regulated under Alberta’s Weed Control Act.
The Alberta Invasive Species Council advises that all parts of the plant are poisonous and should be disposed of in the garbage. According to the City of Airdrie, invasive weeds must never be placed in compost.
“Do not place in your organics cart as these can compromise the end product of compost,” the city says on its website.
According to Rocky View County, black henbane is a biennial or annual plant in the nightshade family. It is poisonous to humans and livestock if ingested.
“Symptoms include impaired vision, convulsions, coma, and in occasional severe situations, death from heart or respiratory failure,” the county says.
The Government of Alberta notes the plant contains toxic alkaloids. Symptoms of poisoning are the same in humans and animals.
Black henbane, or "Hyoscyamus niger," was introduced from the Mediterranean. It reproduces only by seed and has a historical association with medicinal and hallucinogenic uses.
The plant emits a foul odour and is sometimes referred to as “stinking nightshade.” It can grow taller than one metre and is covered in greasy hairs.
Flowers are pale yellow with deep purple veins and throats. Each plant can produce up to 500,000 seeds per growing season. The seeds can remain viable in soil for about four years.
Black henbane thrives in full sun and well-drained soils. It does not tolerate shade. Leaves are large, shallowly lobed and strongly scented. The fruit forms an urn-shaped capsule that bursts to release the seed.
Despite its historical use, the province warns against cultivation. “Gardeners should never grow non-native plants that could escape cultivation,” the Alberta factsheet says.
Control methods include mowing, hand-pulling and burning. Gloves and protective clothing are recommended. Mature plants should be handled carefully to prevent the spread of seeds.
While livestock usually avoid the plant when fresh, it retains its toxicity in dried form and may be consumed if baled with forage.
No selective herbicides are currently registered for black henbane in Canada. Alberta Agriculture and Irrigation advises landowners to confirm product registration with the Pest Management Regulatory Agency before applying any chemical controls.
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