Common Noxious Weeds in Alberta – Perennial Sow-Thistle

Perennial Sow Thistle is a perennial that is commonly confused with Annual Sow-Thistle and Prickly Lettuce.

Perennial weeds grow from root stalks year after year.  Perennial weeds spread by seeds and roots, and therefore the entire plant must be destroyed.

Classification: Noxious Weed

Recognizable features:

Stem:  Upright, leafy at the base with only a few leaves on the stem, up to 2 meters tall

Leaves:  Initally form a rosette, later become alternate, up to 20 cm long, clasp thee stem, variable, deeply lobed with spiny edges to smooth leaf margins, color varies from light green to dark green

Flowers:  Small deep yellow flowers clustered into a head to resemble a single flower, each flower head up to 4 com in diameter, heads arranged in a loose terminal cluster with approximately 20 heads per plant

Distinguishing Perennial Sow Thistle from Annual Sow-Thistle and Prickly Lettuce

Perennial Sow-Thistle spreads by seed and by extensive underground roots, whereas Annual Sow-Thistle spreads only by seed and has a smaller root system.

Perennial Sow Thistle is also easily distinguished from Prickly Lettuce as it does not have the distinctive ridge of spines on the midrib on the underside of the leaf that is associated with Prickly Lettuce.  The entire plant contains a milky juice.  Feathery hairs (pappus) attached to the seed aid in dispersal.

Green Oasis offers a variety of weed control services to help you get rid of those pesky weeds including 3 lawn care packages.

Contact your local office to learn more:

Calgary:                                                                Red Deer:

Tel:  403-206-9900                                             Tel:   403-358-3339

Email: CALGARY@GREENOASIS.CA               Email: REDDEER@GREENOASIS.CA

Information compliments of Agricultural Industry, AAA Fieldmen, Environment, Health & Safety Handbook.

For more information on Perennial Sow Thistle, check out this fact sheet issued by the Alberta Invasive Species Council at www.abinvasives.ca – Perennial Sow-Thistle Fact Sheet.