Horseweed

Horseweed (Erigeron canadensis) is in the Sunflowers, Daisies, Asters, and Allies family (Asteraceae). Across the U.S., iNaturalist users have logged 1,536 research-grade flowering observations of it in our sample, peaking in August.

Nationally it blooms mainly from August to September, but timing varies a lot by state and elevation — see the table below.

When to photograph Horseweed: observations by month (U.S.)

About Horseweed

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.From Wikipedia via iNaturalist — article, CC BY-SA.

Horseweed by state

Main season = months with at least 30% of the state's peak-month count.

Related wildflowers (Sunflowers, Daisies, Asters, and Allies)

black-eyed SusanRudbeckia hirta

Common YarrowAchillea millefolium

White SnakerootAgeratina altissima

ChicoryCichorium intybus

Lawn daisyBellis perennis

Philadelphia fleabaneErigeron philadelphicus

Pearly EverlastingAnaphalis margaritacea

Blue MistflowerConoclinium coelestinum

Photography tips

• Photograph flowers on calm, overcast mornings to avoid wind blur and harsh shadows.
• Get low: a shallow depth of field (f/2.8–f/5.6) isolates a bloom against soft color.
• Stay on trails — trampling meadows kills plants and ruins next year's display.
• Try a kaleidoscope abstract of a single bloom with our online kaleidoscope tool.

FAQ