Giant Ragweed





Giant Ragweed

(Ambrosia trifida)

Interesting Information About Plant:

     Giant ragweed is a very pesky plant. Is affects the crop’s of farmers causing reduced yields, and it also a major contributor to allergies, specifically hay fever. Ragweed is also a plant of concern in the global warming issue, because tests have shown that higher levels of  carbon dioxide will greatly increase pollen production. On dry windy days, the pollen will travel many kilometers. When the humidity rises above 70%, the pollen tends to clump and is not so likely to become airborne.

     The plant does have some helpful uses for  people and animals though. Preparations made from leaves and roots of ragweeds have been used by native peoples as astringents, skin disinfectants, emetics, antidotes, and fever reducers. Teas or tinctures have been used for the treatment of fevers, pneumonia, nausea, intestinal cramps, diarrhea and menstrual disorders. Poultices from rag weeds are applied externally to insect bites, rheumatic joints and various skin conditions. The Kiowa rolled the plant up with different sages for use in sweathouses. Ragweed pollen is harvested commercially and manufactured into pharmaceutical preparations for the treatment of allergies (immunotherapy). In terms of wildlife, the seeds of ragweed are rich in oil, and the seed production per plant is enormous. Some of the seeds will remain on the plant into winter and are forage for birds and other wildlife. Seeds of Ambrosia species are a staple in the diet of game birds, especially the bobwhite quail, and for many songbirds including the goldfinch, song sparrow, white-throated sparrow, and the junco. 


Scientific Name: Ambrosia trifida

Family Name (Scientific and Common): Asteraceae (Aster)

Continent of Origin: North America                  

Plant Growth Habit: Upright Herbaceous 

Height at Maturity: More than 10 Feet

Life Span: Annual (herbaceous)  

Seasonal Habit: Herbaceous That Dies Back in Winter   

Growth Habitat: Full Sun 

Manner of Culture: Weed

Thorns on Younger Stem: No

Cross Section of Younger Stem: Roundish   

Stem (or Trunk) Diameter: Between the Diameter of a Pencil and a Broom-Handle 

Produces Brownish Bark: Yes 

Bark Peeling in Many Areas: No

Characteristics of Mature (Brownish) Bark: Lines Go Horizontal

Type of Leaf: Flat, Thin Leaf  

Length of Leaf (or Leaflet): Between the Length of a Credit Card and a Writing-Pen    

Leaf Complexity: Palmately Compound 

Edge of Leaf: Serrated

Leaf Arrangement: Opposite 

Leaf has Petiole: Yes 

Patterns of Main-Veins on Leaf (or Leaflet): Palmate

Leaf Hairiness: Somewhat hairy

Color of Foliage in Summer: Green 

Change in Color of Foliage in October: No Change    

Flowering Season: Summer and Autumn

Flowers: Tightly Clustered  

Type of Flower: Like a Pine Cone 

Color of Flower: Green  

Shape of Individual Flower: Spike

Size of Individual Flower: Smaller than a Quarter 

Sexuality: Male and Female on Same Plant

Size of Fruit: Smaller than a Quarter / Between a Quarter and the Length of a Credit Card / Larger than the Length of a Credit Card

Fruit Fleshiness: Fleshy/ Dry

Shape of Fruit:    Spherical / Long Pod / Winged / Acorn-like

Color of Fruit at Maturity: Green / Red / Yellow-Orange / Brown or Dry

Fruit Desirable to Birds or Squirrels: Yes / No   

Common Name(s): Giant Ragweed, Great Ragweed, Tall Ragweed

Louisville Plants That Are Most Easily Confused With This One: Common Cocklebur

Unique Morphological Features of Plant: Extremely tall

Poisonous: None of Plant

Pestiness (weedy, hard to control): Yes  


Page prepared by: 


Jeffrey Davis                                    

November 2004

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© Bellarmine University, Louisville, KY 2002-2004