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FWG invasive plant fact sheet Common Burdock (Arctium minus) Common Burdock, a member of the Compositae family, is a plant of open, sunny, disturbed sites: roadsides, rail tracks, old fields, meadows, and forest edges. While it grows best on moist fertile soils it tolerates various conditions. It cannot withstand repeated cultivation. Although described as a biennial, burdock is really a short-lived perennial (a "facultative" biennial). • A basal rosette and deep taproot grow in the first year. Flowering can take up to 5 years depending on site conditions, but once this occurs the plant dies. Burdock can grow more than 2.5 metres in height. • Triangular leaves are broad, coarse, alternate and resemble those of rhubarb. Flower heads consist of a thistle-like bur with spiny bristles topped by a cluster of small purple florets. The flowers grow in the leaf axils and the tip of branches, either singly or in small groups. Flowering is from mid-July through late summer. • The prickly seed-bearing burs readily attach to anything brushing against them, thus ensuring widespread seed dispersal. Studies show an average of 100 burs per plant, each bur containing approximately 40 seeds. However, other studies suggest upwards of 15,000 seeds per plant are produced. Seeds generally mature by September and are spread throughout the winter and spring. Various insects pollinate burdock, particularly honeybees, bumblebees and leaf-cutting bees. Burdock reproduces only by seed. • Studies variously indicate a seed survival rate of from 2 to IO years. • Although native to Eurasia, burdock is now naturalized throughout North America where it has been known for over 250 years. Control Be very careful about disposing of burdock seeds that have hitched a ride on you or your pet! • Removing all flower heads including those in the leaf axils, has proven relatively effective. However, buds can re-form after cutting so monitoring is essential. • Cutting back the first year basal rosette and digging out the taproot has been shown to have a good degree of success. However, some studies report that new plants will grow from any root left in the ground. • Removal of mature burs is difficult but effective . Burs must be bagged and disposed of. • There is no known bio-control agent for burdock at present, although a moth, Metzneria lappella , has been shown in some studies to reduce the viability of burdock seeds. ©Fletcher Wildlife Garden 613-234-6767, fletcher@ofnc.ca . www.ofnc.ca/fle tch er.php Text and photos: Christine Hanrahan