Nodding thistle is found in pockets around the province, but mainly in southern Alberta.
This noxious weed is a prolific seed producer — a single flower can produce up to 1,200 seeds and a single plant up to 100,000 seeds.
It can be recognized by the solitary large red to purple flowers at the end of stems. The leaves are dark green with silvery margins and when the plant matures, the flower ‘nods.’ This aggressive plant can grow up to 2.5 metres (eight feet) tall and has multiple branched stems all covered in sharp spines.
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Nodding thistle is a biennial — which means it takes two years to complete its life cycle — and it can be controlled by hand-picking, mowing, or cultivating if control is done prior to the plant going to seed. A suitable herbicide (always read the label) can also be effective, especially if applied in the first year of growth at the rosette stage.
For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.
– By Laura Poile Agricultural Services Officer, Rocky View County
