Latin name: Ambrosia trifida & Ambrosia trifida var texana
Common name: Giant ragweed & Texas giant ragweed
Season: Early spring through early fall
Edible: Yes, seeds, greens, buds, and flowers. But see potential toxicity warning below
Flavor: Fair
Medicinal: Possible
Nutritional: protein and fats for the seeds, presumably standard green nutritional values for greens
See below for information regarding allergies and potential toxicity
Identification difficulty: Novice when mature, Intermediate when young
Identification note: If you live in a region where giant hogweed, Heracleum mantegazzianum, is known to grow, pay especial attention to the look-a-likes section of this article. Giant hogweed is deadly poisonous and can cause blindness and chemical-like burns from simple contact.
Please note, I am honestly not sure if the images I have here are for giant ragweed, A. trifida, or its subspecies, the Texas giant ragweed, A. trifida var. texana. The share edibility and identification features.
Giant ragweed distribution
Giant ragweed is a native North American plant found throughout most of southern Canada, 47 of the 48 continental United States (comically avoiding Nevada), and southern and central Mexico. It has been introduced and become invasive throughout much of Europe, parts of the Middle East, and east, southeast and northeast Asia. As always, my guides are intended only for readers in the United States, as I don't know about look-a-like species in other parts of the world.
Giant ragweed and allergies
Ragweed pollen is second only to mold when it comes to the likelihood of triggering allergies in humans. Ragweed is generally the true cause of so-called "hay fever" in the late summer and fall, though this often gets attributed to goldenrod, or, well, hay.
For anyone who has a high sensitivity to pollen-related allergies, asthma or any other raspatory disorder, I would advice avoiding this plant when it's flowering, including not consuming ragweed flowers. While it is possible that consuming ragweed pollen might help build immunity, there is no clear evidence backing that AND it's pretty much impossible to gather and use without inhaling a significant amount of pollen. Marie Viljoen of Gardenista recommends wearing a mask. I recommend foraging it before it begins pollination, so in late May, June or early July.
In large part due to climate change, the range of introduced ragweed is spreading rapidly. Ragweed also produces more pollen in warmer years, increasing the allergy risk with global warming.
Do an allergy test before consumption
Despite the high incidence of allergies to the pollen, what we know about the greens indicates they are safe for most people. Still, I would definitely start with a small amount at first and if you have ragweed pollen allergies, even do an allergen test on the greens before eating them. An allergen test involves grinding up a few leaves into a paste using a mortar and pestle. Then rub the paste over the inside of your elbow. Allow to sit for around 2 minutes then rinse off. Wait up to 5 days and see if the area develops any reaction, such as redness, blistering or itch. If you see any reaction, do not eat this plant, even in small amounts. Of course, if you have a severe reaction, even to a skin test, consider seeking out immediate medical attention.
Giant ragweed history as a food crop
Seeds of a cultivated form of giant ragweed have been found in ancient sites of the Native Peoples of the Americas, most notably those of the southwest and plains states, including the Cheyenne, the Sioux and the Osage.
These seeds are much larger than any that grow naturally, indicating that giant ragweed was important enough to prioritize size (and potentially nutritional content) when choosing which strains to cultivate. Despite some sources claiming that giant ragweed was merely ritual or medicinal in use, this focus on size would indicate food use. Other sources agree that giant ragweed was most likely cultivated for its seeds as a source of protein and fat. This cultivation goes back at least 2000 years, but ends between 500-800 years ago, most likely due to the spread of maize from the south. Maize (the precursor to corn) naturally grows larger and, while it lacks in protein and fat, it is higher in caloric value, due to being primarily carbohydrates. Additionally, the calories in maize are easier to utilize, since they do not require dehulling or winnowing.
Despite significant evidence of the seeds being eaten and even cultivated for larger yields, there is scant evidence that the greens were eaten, though many native tribes used them medicinally and/or ritualistically. Despite no clear history of human consumption, the foliage is desirable for most livestock.
Ragweed seeds make up an important part of the diet of game birds and migratory birds, small mammals and even larger mammals like deer.
Giant ragweed identification (mature plants)
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| A massive stand of giant ragweed, showing average mid-summer height of 4-6 feet |
Plant size and location
- Usually by early summer, June through July, giant ragweed is best identified by it's impressive fully-grown size, when the plants will be anywhere from 5' - 7' tall. However, they start out small, almost like a groundcover plant.
- Plants grow in a variety of conditions, including nearly full shade, but favor full or partial sun. Giant ragweed is a ruderal species, which means it likes to move in on disturbed soil. This means it's often found in creek bottoms and similar areas, but will also pop up where land has recently been cleared, such as for farming or construction.
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| Depending on growing conditions and plant age, giant ragweed leaves vary greatly. |
Leaf shape, size and texture
- Giant ragweed leaves are always large to extra large in size for the size of the plant. Even when the plant is young, they will be over 4" long and 3" wide. When the plant is mature they will be between 8" and 12" long and 8" and 10" wide.
- Giant ragweed leaves are deeply lobbed. When young, the plants may only have 3 lobes but as they mature they should have 5, though sometimes the leaves at the top will still only have 3.
- Giant ragweed leaves have a lot of variety in how they are lobed. Sometimes they resemble maple leaves, with the lobs going down about half the length of the leaf. Other times the lobes will cut much deeper, cutting almost to the center of the leaf.
- The back of the leaves are silvery green in color and the underside of the leaf veins are covered in tiny hairs. This makes the leaf feel almost sandpapery underneath, its also why these greens should probably always be eaten cooked. The fine hairs can irritate the throat.
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| Tiny hairs line the undersides of leaf veins. |
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| During the earlies spring weeks (March 7 here) Giant ragweed leaves will look significantly different from the mature ones |
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| Very early giant ragweed leaves |
Identification of young plants (March - April)
Giant ragweed doesn't really start to bolt until mid to late spring, reaching around 3' - 4' tall by mid-April through May here in Texas. Before that, it stays small (under a foot) throughout March and early April. It even starts out looking like a groundcover.
Very early in the season, the end of February through the first week of March here in north Texas, not only will giant ragweed be low to the ground, it will also almost never have any 5 lobed leaves, they will all be 3-lobed or even 2-lobed "mitten" shaped.
By the middle of March the plants, while still groundcover height, will start to primarily growth their 5-lobed, mature leaf forms. Of course, these young plants will still have some 3-lobed leaves as even mature plants retain some of those.
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| Same plants on March 18, you can see they are starting to grow a number of 5-lobed leaves. |
Potential toxicity
First let me say, I see quite a few posts from trusted sources on the edibility of all ragweed greens, flowers and flower buds, including those of the giant ragweed. That said, a European study performed on rats raises some definite concerns. Here are some highlights that jumped out at me:
- The study was performed with common or bitter ragweed, Ambrosia artemisiifolia, not giant ragweed or Texas giant ragweed, Ambrosia trifida and Ambrosia trifida var texana.
- The greens were pureed and added to baked goods to be fed to the rats -- thus the nature of the baked goods could have contributed. Two things are worth noting: Lab rats aren't usually fed baked goods every day for a month and lab rats usually consume vegetables raw, not cooked.
- 24 male rats were fed either 500mg to kg of body weight (considered the low dose) or 1000mg to kg of body weight (considered the high dose), or not fed any ragweed (control group); each group contained 8 rats.
- If my math is correct, this is the equivalent of a 150lb adult eating 1.2 oz or 2.4 oz, respectively, with a serving of leafy greens generally being around 3-4 oz.
- The rats were fed the specified amounts every day for 28 days.
- Rats fed the low dose exhibited reduced liver function and reduced triglyceride levels.
- Rats fed the high dose exhibited increased carbamide levels, indicative of more severe kidney and liver problems.
- Two of the rats were subsequently discovered to have had a genetic kidney disease, however they took the impact of the disease out of the results, and carbamide levels were still elevated in the high dose group.
- Both low dose and high dose rats exhibited elevated brain weights, indicative of swelling.
- I personally would not consume greens from the bitter or common ragweed, A. artemisiifolia. It is well-documented that in many cases the more bitter a green is, the more likely it is to be toxic in some way.
- That said, I continue to have occasional, modest-sized servings of giant ragweed, A. trifida var texana, which is much milder in flavor, has historical use as a food crop (at least for seeds), and which currently has no study with potentially disturbing results.
- I do not have reduced or impaired kidney or liver function, nor do I have any family history of kidney or liver disease. If I did, I personally would not consume this plant.
- I would not eat servings of this plant more than 4-6 times a month, and not more than 2-3 times on sequential days.
- I would only eat the leaves of this plant cooked.
Medicinal and nutritional information
The seeds contain 47% protein and 38% fat by weight. (Source: Sustainable Agriculture Research and Education) But there is no reliable information I can find regarding the nutritional value of the leaves. The topic was raised in the European Parliament in 2015, but it appears as if no funding was dedicated to the research.
Look-a-like plants
Cut-leaf coneflower, mildly toxic
When young, the leaves of cut-leaf coneflower, Rudbeckia laciniata, can resemble those of a young giant ragweed. However if you look closely, you will see that cut-leaf coneflower leaves are oddly pinnately compound. There is a 3-lobed terminal leaflet with 2-4 irregularly-lobed leafletted (1-2 on each side) below it. Giant ragweed leaves are deeply lobed, but not compound. Additionally, giant ragweed leaves are serrated but the cut-leaf coneflower's terminal 3-lobed leaflet is smooth. Once the plants are blooming, it's very easy to tell them apart.
Even when mature, cut-leaf coneflower leaves will resemble giant ragweed leaves. The distinguishing factor is that the lower lobes (near the stem) on coneflower will be more deeply indented than the lobes at the end of the leaf.
Whereas, the lobes on mature ragweed leaves are either equal in depth or the end of the leaf will be more deeply lobed than by the stem.
It's important to know that cut-leaf coneflower also grows to be 4-6" tall, meaning you can't use height as a distinguishing factor.
Cut-leaf coneflower is considered mildly toxic, but an adult is unlikely to be able to eat enough to be dangerously poisoned.
See this plant on Illinois wildflowers and on Minnesota wildflowers
Giant hogweed, deadly poisonous & poisonous on contact
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| Giant hogweed image from contributer Stefan.lefnaer on Wikimedia Commons |
Giant hogweed, Heracleum mantegazzianum, doesn't really look very much like giant ragweed when mature--except in that they are both true giants. But given how very dangerous giant hogweed is, I thought it deserved a mention. Not only is giant hogweed deadly if consumed, it's one of the few plants in North America that can cause contact burns on the skin or even blindness if it gets into the eye.
Giant hogweed could be confused with giant ragweed when it's young.
Like giant ragweed, giant hogweed can grow to 5', 7', 8', even 10' tall. Giant hogweed can actually grow even taller than that, though that is rare. Giant hogweed leaves are suitably giant, sometimes reaching over 2' long!
Like giant ragweed, giant hogweed leaves are palmately veined, deeply lobed and have serrated edges. As the leaves mature the lobing will become almost compound in nature, a feature which we never see in giant ragweed.
However, when youngish, as in the picture above, the leaves will not always display this compound attribute and can look fairly similar to giant ragweed leaves of similar size. Note especially those smaller leaves in the middle of the plant. The best way to familiarize yourself is to study images of both leaves, as the differences are visually distinctive, but hard to describe.
Giant hogweed have red or purple blotches on the stems, and they do NOT have hairs on the leaf undersides. However, it is difficult to notice these differences while maintaining a safe distance and not touching the plant.
Other look-a-likes for young plants
As long as you are harvesting mature giant ragweed plants, you are unlikely to be confused by any of the look-a-likes below. This is why I say mature giant ragweed is a beginner plant. But if you are trying to forage it young please look out for the following similar looking plants:
- Avens plants, specifically white Avens - poisonous
- Ground elder/goutweed/bishop's weed - edible
- Summer grape or swamp grape, Vitis aestivalis - edible
- Sassafras - traditionally edible, now potentially linked to cancer
- Mulberry - edible
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