Science & Nature • Plants

Ragweed

Ragweed is a group of weedy flowering plants in the genus *Ambrosia* in the aster family (Asteraceae).

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Ragweed is a group of weedy flowering plants in the genus Ambrosia of the aster family. Many species are native to North America, and their wind-blown pollen is a major cause of seasonal allergies, especially in late summer and early fall.

Description

Ragweed refers to several species of weedy plants in the daisy family (Asteraceae). Common ragweed is an annual plant with green stems and divided leaves, and it produces small, inconspicuous flowers in spikes. Ragweed is a member of the aster family, which includes plants such as the Aster (plant).

Allergy importance

Ragweed pollen is widely recognized as a major aeroallergen in North America. Because the pollen is carried by wind, it can travel widely and trigger seasonal allergic rhinitis, often called hay fever. Like walnut, ragweed produces wind-borne pollen.

Seasonality and habitat

Ragweed typically flowers from late summer into fall. It grows best in sunny, disturbed soils such as fields, roadsides, vacant lots, and other open areas. Ragweed, like blueberry, is native to North America.

Identification and lookalikes

Ragweed is usually identified by its green, hairy stems, finely divided leaves, and greenish flower spikes. It is commonly confused with goldenrod, which has bright yellow flowers and is pollinated by insects.

Key facts

Ragweed is the common name for plants in the genus Ambrosia.
Most species are native to North America.
Ragweed pollen is a major trigger of hay fever and other seasonal allergy symptoms.
Common ragweed is typically a weed of disturbed ground, roadsides, and open fields.
Ragweed blooms in late summer, with pollen often peaking in mid-September in many areas.

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Canadian context

Ragweed is relevant to Canadian readers because it is a common seasonal allergen in parts of Canada, especially where disturbed land and late-summer pollen exposure are common.

Frequently asked questions

What is ragweed?

Ragweed is a group of weedy flowering plants in the genus Ambrosia of the aster family. Many species are native to North America, and their pollen is a common allergen.

What are ragweed allergy symptoms?

Common symptoms include sneezing, runny or stuffy nose, itchy eyes, itchy throat, coughing, and sometimes asthma flare-ups or fatigue.

When is ragweed season?

Ragweed season is usually late summer through early fall, often beginning in early or mid-August and peaking in mid-September, ending with the first frost or colder weather.

How do I identify ragweed?

Look for a green, hairy annual weed with finely divided leaves and small greenish flowers arranged in spikes. It often grows in disturbed, sunny areas such as roadsides and vacant lots.

What is the difference between ragweed and goldenrod?

Ragweed has small, greenish flowers and wind-blown pollen, while goldenrod has bright yellow flowers and is pollinated by insects. Goldenrod is often blamed for allergies, but ragweed is the more common cause.

References

Encyclopaedia Britannica — https://www.britannica.com/plant/ragweed
Supports: Ragweed is a genus in the aster family; most species are native to North America; pollen is a major cause of hay fever in late summer.
Asthma and Allergy Foundation of America — https://aafa.org/allergies/types-of-allergies/pollen-allergy/ragweed-pollen/
Supports: Ragweed allergy season timing, symptoms, and comparison with goldenrod; ragweed plant characteristics and pollen production.
Pennsylvania Department of Environmental Protection — https://www.pa.gov/agencies/dep/programs-and-services/air/bureau-of-air-quality/pollen/ragweed-identification
Supports: Physical identification features of common ragweed and blooming timing.
Allergy & Asthma Network — https://allergyasthmanetwork.org/allergies/pollen-allergy/ragweed-allergy/
Supports: Seasonal timing, symptoms, and the ragweed-versus-goldenrod distinction.