Summary ²

Erigeron canadensis (synonym Conyza canadensis) is an annual plant native throughout most of North America and Central America. It is also widely naturalized in Eurasia and Australia. Common names include horseweed, Canadian horseweed, Canadian fleabane, coltstail, marestail, and butterweed. It was the first weed to have developed glyphosate resistance, reported in 2001 from Delaware.

Description ³

Family:
Asteraceae (Aster)

Height:
½ to 7 feet

Leaves:
Alternate leaves are crowded but fairly evenly spaced along the full length of the stem, appearing almost whorled. Leaves are narrow (up to ½”), and longer near the bottom of the plant (up to 4”), becoming shorter as they ascend the stem. Leaf margins are covered in stiff hairs. Lower leaves typically have widely spaced teeth.

Flower:
Flowers (up to ⅛” across) are inconspicuous and tube-shaped, with very small white to light pink petals and yellow centers. The base of each bud-like flower is a light-green bract several times the length of the petals. Flowers grow in branching clusters (panicles) from the top of the plant, with the largest cluster at the top of the main stem and smaller clusters growing from lateral branches near the top of the plant.

Bloom time:
July-October

Nicknames:
Horseweed, Canada Fleabane, Marestail, Coltstail, Butterweed

Habitat:
Canadian Horseweed grows in full sun, and average to dry, fertile, loamy soils. It is commonly found in disturbed areas, including prairies, fields, roadsides, vacant lots, construction sites, and gardens.

Wildlife Benefits:
Flowers are attractive to small bees, wasps, flies, and a variety of other insects.

Can I plant this in my garden?
While native, this species is not an ideal garden plant due to its weedy, aggressive nature. As a result of its wind-dispersed seeds, it is frequently found as a volunteer in gardens with exposed topsoil, and has become invasive across much of Eurasia. To prevent its spread on and around your property, hand-pull plants before they go to seed, taking care to remove the taproot to prevent resprouting. Herbicide may be necessary to control more widespread invasions.

References:
https://www.minnesotawildflowers.info/flower/canadian-horseweed
http://www.illinoiswildflowers.info/weeds/plants/horseweed.htm
https://plants.ces.ncsu.edu/plants/erigeron-canadensis/

Range ³

Sources and Credits

1. (c) Ramsey-Washington Metro Watershed District, all rights reserved, uploaded by Ramsey-Washington Metro Watershed District
2. Adapted by Ramsey-Washington Metro Watershed District from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Erigeron_canadensis
3. (c) Ramsey-Washington Metro Watershed District, some rights reserved (CC BY-SA)

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