Common Ragweed, Hay-Fever Culprit

A common ragweed plant coming up out of the ground.
David Beaulieu

Learn what common ragweed looks like, what harm it causes, and how to get rid of any growing in your yard. This weed is unattractive as well as noxious. The challenge in removing it is that most people have trouble identifying it because it is a nondescript plant.

Taxonomy and Botany of Common Ragweed

Plant taxonomy gives common ragweed the scientific name of Ambrosia artemisiifolia. Although its giant relative (Ambrosia trifida) is a very different-looking plant from the common variety, both are responsible for hay fever.

Common ragweed is classified botanically as an annual. It is also considered a broadleaf weed. So is its taller cousin, Ambrosia trifida.

Goldenrod Wrongly Blamed for Hay Fever

Common ragweed is a rather unremarkable plant. That is why the lovely goldenrod is commonly blamed for causing hay fever when common ragweed is the real culprit. Goldenrod and common ragweed both bloom in late summer or early fall (depending on where you live). Being by far the more conspicuous of the two, goldenrod has become the scapegoat for hay fever, while the true villain goes unnoticed, lurking in the grass. 

Weed Identification: What It Looks Like, Where It Grows

The most remarkable thing about common ragweed's appearance is that it bears an intricately toothed leaf. The weed's tan-green flower stalks are inconspicuous. They look a bit like those of common plantain (Plantago major), a common lawn weed. This major source of hay fever can reach 1 to 6 feet in height (but in a yard subjected to foot traffic, mowing, weed wacking, etc., it is usually found growing at the smaller end of that spectrum). 

The plant is indigenous to North America. It can be found in every state in the United States except for Alaska, and it is widespread in Canada, too. The plant thrives in disturbed soils and is frequently found along roadsides.

Getting Rid of This Weed: Best Eradication Method

Since it spreads via seed, efforts at keeping common ragweed from spreading should focus on preventing seed production. As a bonus, if eradication occurs prior to flowering, you will reduce hay-fever pollens. Hand-pulling is the best method of getting rid of common ragweed for homeowners. The plants are easy to pull, as they have shallow root systems. But put your garden gloves on first to do your weeding, because this plant can also cause skin rashes.

Origin of the English and Scientific Names

"Ragweed" is a reference to the ragged (that is, deeply indented) look of its leaves. The second element of its scientific name (artemisiifolia) refers to its foliage, whose shape resembles that of another group of plants, the artemisias. Some artemisias are attractive enough to be used as landscape plants, examples being Silver King artemisia and Silver Mound artemisia

But not all artemisias are welcome in the landscape. Mugwort (Artemisia vulgaris), also called "common wormwood," is among the weediest-looking of the weeds. Even if you cannot identify it, you have almost certainly seen it if you live in eastern or central North America, where it has naturalized and is often the most prominent plant seen growing along roadsides in autumn. Like common ragweed, it flowers in late summer or early fall, and its pollen can cause hay fever.

Common Ragweed, Hay Fever, and Skin Rash

Together, common ragweed and giant ragweed account for most of the hay fever experienced in North America in the fall. Symptoms of hay fever are sneezing and runny nose, along with itchy eyes.

Although the name, "hay fever," alludes to the "haying" season in the fall, people often refer to allergies experienced at any time of year as "hay fever." Thus birch trees, for example, are spoken of as a major source of hay fever in eastern North America, even though the hay fever resulting from their pollen occurs in spring, not fall.

Your efforts to eradicate common ragweed will presumably be limited to your own yard. So no matter how good a job you do at getting rid of common ragweed, its pollen will still be in the air. What is a hay-fever sufferer to do? Stay inside all September? Well, at least you can try to minimize your outdoor activities when the pollen count is highest (generally between 10 a.m. and 4 p.m.). This practice will not eliminate your hay fever, but any lessening of the symptoms will make life easier to endure.

While more often associated with hay fever, common ragweed is also one of the plants that cause skin rashes (known, technically, as "allergic contact dermatitis").