Noxious black henbane taking root in Calgary

Black henbane, an invasive and toxic plant species, is becoming more common in Calgary green spaces, thanks in part to the weather.

The weed is listed as noxious under Alberta’s Weed Control Act. It has a yellow flower with purple veins but is poisonous to humans and animals, and can be deadly if ingested.

The city’s pest management team says 311 calls for the plant have increased this year.

“Last year we had 93 reports for the whole year, this year we are at 73,” said Sarah Vardiel, Integrated Pest Management Technician with the City of Calgary. “The City’s mandate is to control the spread of it so if people find it can let us know.”

While it’s too early to say if there will be a higher total number of calls, the dry weather has created conditions for the toxic weed to spread.

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“Weeds tend to be better competitors in poor conditions,” Vardiel explained. “So, when we’re having very dry conditions, those weeds just tend to pop up and out-compete those native species.”

Calgarians who find black henbane on their property are encouraged to remove the plant, but need to dispose of it in their black bin rather than the green compost bin.

“We don’t want this in our green carts, particularly because those go to a compost facility and we don’t want to be spreading this weed around through compost later on,” said Vardiel.

Kath Smyth, a horticulturalist with the Calgary Horticultural Society, said the dry conditions have caused the weed to seed quickly which will naturally increase its spread.

“When the seed head opens, it’s almost like an explosion and even the slightest wind… they float on water… the seeds can survive for up to twenty years,” said Smyth.

Toxic to come in contact

All parts of the plant are poisonous to humans and animals. It is a member of the nightshade family and causes a rash if it comes in contact with exposed skin.

“When you touch or handle the foliage, it burns your hands,” Smyth said. “It’s like touching stinging nettles but worse. It’s worse than poison ivy in my mind.”

It is also poisonous to dogs and other pets, causing vomiting and diarrhea.

When trying to remove it from the garden, Smyth warns proper equipment is key to walking away unscathed.

“If you want me to touch this, we’re wearing gloves,” laughed Smyth. “I wear a scarf because a friend of mine once got a burn on her neck from it.”

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Black henbane is an annual plant that survives through the winter, meaning the only way to get rid of the plant is by digging it up, along with its entire root system.

“The root systems grow quite far down,” said Smyth. “The success of that plant’s survival is because of the deep roots.”

Smyth says the plant should be removed as soon as it is discovered because black henbane can grow up to six feet tall and it becomes increasingly difficult to get rid of the larger it gets.

“When they’re really, really big, they’re impossible to prune,” said Smyth.