This quick-spreading weed gets an early start

Noxious weeds: Canada thistle

Seed from Canada thistle can germinate eight to 10 days after flowering, but roots — not seeds — are the main way that this noxious weed spreads.
Reading Time: < 1 minute

Spring brings lovely native flowers, but also noxious weeds.

The aggressive perennial Canada thistle is a favourite of disturbed soils of all types. It starts sending shoots from horizontal roots to the surface of soil around mid-April, with flowers to follow in mid-June and continuing throughout the summer.

Easy to distinguish from other weeds, this particular thistle has grooved, upright, hollow and woody stems that branch near the top of the plant. The leaves, generally lobed and spikey, have a tendency to vary in appearance. Usually purple, pink, or white, the flowers on these bothersome plants form at the ends of the stems in clusters of one to several.

It has been estimated individual plants live around two years, but are continually replaced by new shoots on its extensive root system. Maintaining healthy plant cover and reseeding disturbed areas with a desired plant species is the most recommended preventive measure. If however, you find Canada thistle on your land, killing the roots is the only effective control method. Integrated management plans are the most effective long-term strategy for reducing infestations.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a conservation assistant for Red Deer County.

About the author

Association of Alberta Agricultural Fieldmen's recent articles



Stories from our other publications