Photo by Melody

PlantFiles: Giant Ragweed, Great Ragweed, Palmate Ragweed
Ambrosia trifida

Family: Asteraceae (ass-ter-AY-see-ee) (Info)
Genus: Ambrosia (am-BRO-zhuh) (Info)
Species: trifida (TRY-fee-duh) (Info)

Synonym:Ambrosia trifida var. trifida


6-8 ft. (1.8-2.4 m)
8-10 ft. (2.4-3 m)
10-12 ft. (3-3.6 m)
12-15 ft. (3.6-4.7 m)

24-36 in. (60-90 cm)

Not Applicable

Sun Exposure:
Full Sun

Handling plant may cause skin irritation or allergic reaction
Pollen may cause allergic reaction

Bloom Color:

Bloom Time:
Mid Summer
Late Summer/Early Fall


Other details:
May be a noxious weed or invasive
Drought-tolerant; suitable for xeriscaping
Average Water Needs; Water regularly; do not overwater

Soil pH requirements:
6.1 to 6.5 (mildly acidic)
6.6 to 7.5 (neutral)
7.6 to 7.8 (mildly alkaline)

Patent Information:

Propagation Methods:
From seed; direct sow outdoors in fall
From seed; stratify if sowing indoors
Scarify seed before sowing

Seed Collecting:
Bag seedheads to capture ripening seed
Properly cleaned, seed can be successfully stored

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There are a total of 19 photos.
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1 positive
1 neutral
6 negatives

Gardeners' Notes:

Neutral plant_it On Jun 1, 2013, plant_it from Valparaiso, IN wrote:

It's a native plant (native to the U.S. anyway), so that's a positive. Other than that, I can't see that it has that much going for it. The leaves and seeds aren't particularly liked by wildlife, so I certainly wouldn't add this to the wildlife garden. And it's an allergy sufferer's worst nightmare.
This huge plant is probably an allergy sufferer's worst nightmare.

"It has some ecological value to various moths, but otherwise is less important than Ambrosia artemesiifolia (Common Ragweed). Giant Ragweed can be distinguished from other Ambrosia spp. (Ragweeds) by its palmately lobed leaves; other Ragweeds have leaves that are pinnatifid or bipinnatifid. The name of this genus of plants refers to ambrosia, "the food of the gods" in antiquity. This seems like a strange name for a group of unattractive plants, unless it refers to the value of the seeds of certain species from a bird's point of view."

Negative Malus2006 On Feb 19, 2008, Malus2006 from Coon Rapids, MN (Zone 4a) wrote:

Giant ragweed are more oftenly seen in gardens than common ragweed but in other locations such as roadside common ragweed is far the most often. It is easily identify by its strongly three lobed leaves that look kind like sassafras but is not woody. It is also common only in certain area like when construction workers clear out all the vegetation on the roadside for a certain period of years before grasses and other agressive species reduce the numbers - it will persists in certain locations. Giant ragweed is easy to control - it is the rain of seeds that comes in from nearby locations that is the main headache for this weed.

Negative Pyrola5 On Dec 16, 2004, Pyrola5 from Bradford, PA (Zone 5a) wrote:

Giant ragweed came up in my flower bed one year,I didn't know what it was so I let it grow. It was GIANT, well over my head. I sent pictures to the county agent. He told me what it was and I dug it out and got rid of it. It never returned. I live in NW PA, so it definitely grows here. My daughter is allergic to ragweed.

Positive BotanyDave On Dec 15, 2004, BotanyDave from Norman, OK (Zone 7a) wrote:

A beautiful weed with an interesting and easily controlled growth pattern. The leaves may be unlobed, or multiple-lobed (although the most common are 3, 5, or 7). Plants are very difficult to transplant, but it can be done if water is used constantly. Seeds need to be outside during winter in order to germinate in the spring- treating in the house is possible but difficult (or they could be treated with various chemicals). Plants in partial shade and damp soil do very well. Mature plants are easily removed with a saw.

Negative trois On Sep 1, 2004, trois from Santa Fe, TX (Zone 9b) wrote:

The plant is attractive. The alergy reaction is not. There is no way to control this plant here without destroying all the native vegitation. We will tolerate it.

Negative melody On Aug 30, 2004, melody from Benton, KY (Zone 7a) wrote:

A common pest weed in these parts. It produces so many seeds that it's place is assured in the ecosystem.

The pollen causes allergic reactions to many people and some folks can get quite sick.

On the up side, the oil rich seeds are a food source to songbirds and other wildlife.

Negative Muckdiver On Jan 31, 2003, Muckdiver from Saint Louis, MO wrote:

I found a way to eliminate the ragweed by cutting the stem near the base, just before it started to bloom in the fall.
A weed-whacker is a good way to do this. Note that seeds remain in the ground and will germinate if the soil is tilled; the seedlings can be pulled if this happens.

Negative lupinelover On Jan 25, 2003, lupinelover from Grove City, OH (Zone 6a) wrote:

Although the seedlings are fairly attractive, this plant should be pulled as soon as it is identified. It grows so large that it is very difficult to dislodge when it is beyond seedling size.


This plant has been said to grow in the following regions:

Brunswick, Georgia
Indianapolis, Indiana
Oakland City, Indiana
Valparaiso, Indiana
Yale, Iowa
Benton, Kentucky
Hebron, Kentucky
Boonsboro, Maryland
Gregory, Michigan
Highland, Michigan
University Center, Michigan
Minneapolis, Minnesota
Belton, Missouri
Cole Camp, Missouri
Piedmont, Missouri
Saint Robert, Missouri
Beatrice, Nebraska
Doniphan, Nebraska
Kearney, Nebraska
Hyde Park, New York
Union Springs, New York
Edmond, Oklahoma
Bradford, Pennsylvania
Arlington, Texas
Austin, Texas (2 reports)
Boerne, Texas
Cleburne, Texas
Dallas, Texas
Frisco, Texas
Garland, Texas
Port Neches, Texas
San Antonio, Texas
Santa Fe, Texas
Radford, Virginia
Falling Waters, West Virginia

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