Ambrosia trifida - L.
Common Name Giant Ragweed, Great ragweed, Texan great ragweed, Bitterweed, Bloodweed, Buffalo Weed, Horse Cane
Family Asteraceae or Compositae
USDA hardiness 1-11
Known Hazards The pollen of this plant is a major cause of hayfever in N. America[222]. Ingesting or touching the plant can cause allergic reactions in some people[222].
Habitats Alluvial waste places, sometimes forming vast pure stands[222].
Range Eastern N. America - Quebec to Florida, west to Manitoba, Colorado and Mexico.
Edibility Rating  
Other Uses  
Weed Potential Yes
Medicinal Rating  
Moist Soil Semi-shade Full sun

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An erect summer annual with some useful medicinal qualities and minor edible and other uses. Bloom Color: Green. Main Bloom Time: Early fall, Late summer, Mid summer. Form: Upright or erect. Common Names include: great ragweed, Texan great ragweed, giant ragweed, tall ragweed, blood ragweed, perennial ragweed, horseweed,buffaloweed, and kinghead. Spanish: Artemisa grande. Germany: Dreilappige Ambrosie; Dreispaltige Ambrosie. Japan: kuwamodoki; oobutakusa. Netherlands: driedeelige Ambrosia. Sweden: tall Ambrosia. USA: bitterweed; buffalo weed; crown-weed; horse-cane; horse-weed; kinghead; tall ragweed.

Ambrosia trifida Giant Ragweed, Great ragweed, Texan great ragweed, Bitterweed, Bloodweed, Buffalo Weed, Horse Cane
Ambrosia trifida Giant Ragweed, Great ragweed, Texan great ragweed, Bitterweed, Bloodweed, Buffalo Weed, Horse Cane
Physical Characteristics
 icon of manicon of flower
Ambrosia trifida is a ANNUAL growing to 2 m (6ft 7in) at a medium rate. It is in flower from Aug to October. The flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and are pollinated by Wind.Suitable for: light (sandy), medium (loamy) and heavy (clay) soils. Suitable pH: acid, neutral and basic (alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers moist soil.


Woodland Garden Cultivated Beds;
Edible Uses
Edible Parts: Oil.
Edible Uses: Oil.

This plant was cultivated by the pre-Columbian N. American Indians, seeds found in pre-historic sites are 4 - 5 times larger than those of the present-day wild plant, which seems to indicate selective breeding by the Indians[207]. The following report is for A. artemesifolia, it quite possibly also applies to this species[K]. An oil is obtained from the seed. It has been suggested for edible purposes because it contains little linolenic acid[61, 183]. The seed contains up to 19% oil[61], it has slightly better drying properties than soya bean oil[183].
Medicinal Uses

Plants For A Future can not take any responsibility for any adverse effects from the use of plants. Always seek advice from a professional before using a plant medicinally.

Antidote;  Astringent;  Emetic;  Poultice;  Skin;  Women's complaints.

The leaves are very astringent, emetic and febrifuge[222, 257]. They are applied externally to insect bites and various skin complaints, internally they are used as a tea in the treatment of pneumonia, fevers, nausea, intestinal cramps, diarrhoea and mucous discharges[222]. The juice of wilted leaves is disinfectant and is applied to infected toes[257]. A tea made from the roots is used in the treatment of menstrual disorders and stroke[222]. The pollen is harvested commercially and manufactured into pharmaceutical preparations for the treatment of allergies to the plant[222].


Other Uses
Dye;  Oil.

A red colour is obtained from the crushed heads[207]. (This probably refers to the seed heads[K].) The sap of the plant can stain the skin red[274]. A positive impact may be seen with a noted decrease in the numbers of plant-parasitic nematodes found in soyabean fields where A. trifida is present (Wang et al., 1998).
Cultivation details
We have very little information on this species but suggest growing it in a sunny position in a well-drained soil[K]. This plant is sometimes cultivated by the N. American Indians for food and medicine[207]. Special Features: North American native, Invasive, Inconspicuous flowers or blooms.
Seed - we have no details for this species but suggest sowing the seed in situ in April.
Other Names
Found In
Weed Potential

Right plant wrong place. We are currently updating this section. Please note that a plant may be invasive in one area but may not in your area so it’s worth checking.

A noxious weed, both in its native range and in areas where it is an introduced and often invasive species. Extremely competitive and is very difficult to control, especially in many broadleaved crops. a declared noxious weed in California, Delaware, Illinois and New Jersey, USA and a quarantine weed in Poland and Russia [1c].
Conservation Status
IUCN Red List of Threatened Plants Status : This taxon has not yet been assessed.
Related Plants
Latin NameCommon NameEdibility RatingMedicinal Rating
Ambrosia artemesiifoliaRoman Wormwood, Bitterweed, Blackweed, Carrot Weed, Hay Fever Weed, Stickeweed, Tassel Weed, Wild Ta23


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Readers comment
David Murray   Mon Feb 03 20:15:50 2003

First, I'd like to say that I really enjoy your site.

Next, I thought you'd like to know about a slight typo... In your Ambrosia trifida fact sheet, you list A. F. Hill's Economic Botany as a source, "the seed contains up to 19% oil [171]."

But, if you look in the book, the entries go from ragi to railroad cars, and from Ambergris to Ammoniacum. This book doesn't say a thing about ragweed. However, the bit about the oil is mentioned in your source #61, A Dictionary of Plants Used by Man -nearly word-for-word.

So, you might want to switch [61] for [171], and leave out the latter.

-Nearly drove me mad; I kept looking through the book and the index, going back and forth until I wrote it all down. :)

Oh yeah, one more thing... male and female flowers are separate: male flowers form most of the terminal cluster, while the female flowers are very inconspicuous and are found at the base of the cluster. -They are not hermaphroditic. And they are Wind pollinated (hense all that allergen trouble).

Well, thank you for listening to me rant about my favorite plant. And once again, you've got a wonderful website!

-David Murray

David   Wed Apr 12 2006
Long time, eh? Since I wrote the last comment, I've been able to track down some of the original reports made about the cultivation of the seeds by the pre-Columbian indians. In short, it didn't happen. There are two major populations of ragweed in the United States: west of the mississippi, seeds are tiny; east of the mississippi, they are very large. The original researcher didn't know this of course, and hypothesized that the large seeds he found meant cultivation had occured- when really he found an area where the two populations met and simply wasn't familiar with the eastern variety. Further research shows that the seeds need to be exposed to the wet and cold of winter to germinate- the seeds found in the pre-columbian indian sites were in protective holes kept out of the cold and wet: there was no way that they were saving seeds to plant again- they simply wouldn't germinate. A report concluded that the seeds wouldn't be a good food source because the seeds were entirely protein- which doesn't make much sense to me, but I will continue to look into it. You may wish to up the medicinal value of the plants, above. I have used the leaves when I get nasty cuts in the field while gathering various experimental plants. I chew up a leaf and place the mash on the gash- it stops the bleeding almost instantaneously. I love this plant. Sincerely, David Murray Botanist
aubrey james shepherd   Wed Sep 27 2006
We get hundreds of birds of numerous species visiting our backyard in September because we allow the giant ragweed to grow to more than 20 feet some years. My wife's asthma reaches a peak in August and early September but she loves seeing the cardinals in the tops and the doves on the ground and always keeps plenty of the plants until the seed is gone. Then we cut it off near the ground and remove the huge plants to compost. primarily outdoor recreation and natural-resource conservation.

David Beaulieu   Sat Sep 30 2006
Hard to believe this plant is related to common ragweed (Ambrosia artemisiifolia). In my region (New England, U.S.), I regularly encounter common ragweed plants that are rather short (under 1 foot), probably because they grow in areas where they are mowed or trampled upon frequently. In undisturbed areas, they do attain a greater height -- but nothing like that of giant ragweed!

Giant Ragweed Introduction to giant ragweed. Pictures of giant ragweed included.

Aubrey James Shepherd   Sat Dec 2 2006
The birds ate most of the seed and the plants died and can be sent to the city mulc-production site. We allowed fewer than usual to grow to maturity so there are relatively few big stallks to remove this winter. We had several inches of rain and then light snow the past few days and the ground is soaked and it is easy to pull the dead plants, but we probably will leave most in the ground and lop them off near the surface to avoid disrupting so much of the dark, rich wetland soil in our yard, Plenty of seed feel to regenerate ambrosia next spring. Robins and cardinals and cedar waxwings cleaned off most of the ripe, red berries of our China honeysuckle bushes and the remainder of the hackberries that held on after the leaves fell from our big, old hackberry trees as the wind and rain came in ahead of the light snow. Those honeysuckle berries always disappear during the first snow of the year in Fayetteville, Arkansas. After the rain and snow, the robins went to work on earthworms, while the cedar waxwings mostly disappeared after finishing off the hackberries! outdoor sport and resource conservation information and photos

Gwen Giffen   Wed Sep 10 2008
I had the worst time indentifying this plant. I was picking elderberries to make jam, and found its pollen all over the elderberries, and I wanted to make sure it wasn't poisonous. Now I know that my jam will have anti-allergy properties. Thanks!
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