Giant Ragweed

Giant Ragweed (Ambrosia trifida) is in the Sunflowers, Daisies, Asters, and Allies family (Asteraceae). Across the U.S., iNaturalist users have logged 911 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 Giant Ragweed: observations by month (U.S.)

About Giant Ragweed

Ambrosia trifida, the giant ragweed, is a species of flowering plant in the sunflower family. It is native to North America, where it is widespread in Canada, the United States, and northern Mexico. It is present in Europe and Asia as an introduced species, and it is known as a common weed in many regions. Its common names include great ragweed, Texan great ragweed, giant ragweed, tall ragweed, blood ragweed, perennial ragweed, horseweed, buffaloweed, and kinghead.From Wikipedia via iNaturalist — article, CC BY-SA.

Giant Ragweed 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