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All About Giant Ragweed

If you suffer from summer hay fever, you’re on high alert when ragweed is in season.

Did you know there are around 50 species of ragweed worldwide, and giant ragweed is the second-most common species? This weed has its characteristics and patterns of growth that separate it from other ragweed species.

Read on to learn how you can identify giant ragweed, eliminate it from your garden, and some surprising health benefits discovered by the Native Americans.

Ambrosia trifida, the giant ragweed.

History of Giant Ragweed

Giant ragweed, or Ambrosia trifida, is a member of the Asteraceae (Composite) family and originated in North America, where it was an early pioneer of distressed soils that became widespread in Canada, the United States, and northern Mexico.

Other names for giant ragweed include great ragweed, Texan great ragweed, tall ragweed, blood ragweed, perennial ragweed, buffalo weed, and kinghead.

Native Americans used this weed for several medicinal purposes. They rubbed crushed leaves on cuts to stop bleeding, and ragweed leaf tea was used to treat illnesses.

Today, it’s a common weed that most people want to eradicate from their lawns, though its medicinal properties still benefit modern-day societies.

Identifying Giant Ragweed

Ambrosia trifida, the giant ragweed.

Giant ragweed emerges similar in appearance to common ragweed. The biggest difference between the two is that giant rag has shallowly lobed leaves compared to common ragweed’s deeply lobed leaves.

Other key identification traits of the weed are its rough stems covered in tiny white hairs and leaves resembling a hand’s palm. Also, it is one of the earliest weeds to appear during North American summers.

The plant can grow up to twelve feet tall, making it difficult to contain when it hits its peak height. Male (staminate) flowers are yellow to green with no pedals, and female (pistillate) flowers are hidden behind clusters of bracts located at the cluster’s base, which spread as the plant grows.

Problems Caused by Giant Ragweed

Ambrosia trifida flowers / Ambrosia trifida grows densely in the wasteland, and its ear-shaped flowers cause hay fever.


Giant ragweed is a large contributor to hay fever. It causes symptoms like a runny nose, sneezing, and itching. People who suffer from asthma can experience flare-ups from breathing in its allergens.

The allergens are most bothersome in late summer, between July and September, because that’s when the flowers on the plant bloom.

Plant Harm

The weed causes harm to plants and can cause slow growth. It is most common in corn, soybean, and cotton fields. This pesky weed can reduce crop growth by 50 percent!

How Giant Ragweed Spreads

Giant Ragweed plants scatter through their seeds. Due to the large seed size, they easily spread through the wind. They are often moved in fields through farm equipment. Birds and other animals also like to eat the plant and will spread the seed while feasting.

Controlling Giant Ragweed

Removing giant ragweed can drastically improve your allergy symptoms and the health of your crops.

Controlling and getting rid of this weed can be troubling because it is becoming resistant to glyphosate, a common ingredient used in weed-killing sprays. Natural remedies may work best to get rid of these weeds.

The good news is, the same remedies that work for giant ragweed should also work for common ragweed.

Natural Remedies

Pull Using Hands

The weed can be pulled with your hands before it gets out of control. Since ragweed is a common source of contact dermatitis, remember to wear gloves while pulling weeds.

If you are especially sensitive to ragweed allergens, you may want to wear goggles and a special mask to protect yourself.

Use a Hoe to Remove the Roots

Use a garden hoe to dig down to the roots when removing larger giant ragweed.

Lawn Mower

A lawn mower can remove a large area of giant ragweed. You must mow at least every two to three weeks because mowing does not remove the weed’s roots. If you mow regularly, eventually, the roots will die.

Don’t Forget Fence Lines

Fence lines are notorious for attracting giant ragweed because that’s where seeds get caught in the wind. Remove the weed from fence lines at first sight before it spreads to the rest of your yard.

Crop Rotation

Crop rotation helps control the weed’s growth in fields because it allows for several types of herbicides to be used, preventing herbicide resistance.

Plant Crops Later

Some farmers have drastically reduced giant ragweed in their fields by planting crops two to three weeks later than usual.

Planting crops later in the season may be effective because this weed appears early, often before the fourth week of May.

Delaying planting until the fourth week of May and doing extra tillage in between reduces the pressure on the land, reducing the weed’s ability to grow.


The most effective weed spray for killing common and giant ragweed is Amine 2,4-D Weed Killer. Apply when the ragweed is young for best results.

Preventing Future Growth

Prevent future giant ragweed attacks by fertilizing and mowing your lawn regularly.

Giant Ragweed Uses

Native Americans and early herbalists used it as a natural medicine, and many naturalists believe these medicinal uses are still relevant today. You want to avoid these remedies if you have a known or suspected ragweed allergy.

Topical Applications

The juice from crushed ragweed leaves has been used to soothe poison ivy and insect bites.

Drinking Tea or Juice

Herbalists have used the root of giant ragweed to create tea as a laxative.

It has also been consumed for many other reasons, such as fever reduction, menstrual discomfort, and relieving hay fever symptoms (which may seem ironic since ragweed is often the root cause of hay fever.)

Frequently Asked Questions

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What animals eat giant ragweed?

Rabbits and grasshoppers eat the leaves. Birds eat the seeds (and enjoy spreading them).

Is it okay to burn giant ragweed?

It was once common to cut ragweed down, dry it out, and then burn it. This method was popular because manually removing ragweed can be bothersome to allergies. However, this method is rarely used today due to the environmental pollution it causes.

Wrapping up Giant Ragweed

Now that you’re up to date on the characteristics of giant ragweed and the methods to control it, you’re ready to start identifying and managing it.

If you feel like you need to learn more about these pesky garden tenants, check out our weeds page to learn all about different weed varieties, treatment options, and surprising information.