Giant Ragweed

ragweed and hoverflyIt is getting closer to that time. Allergy season. If you are not horribly allergic to the Giant Ragweed, you probably know someone who is. This plant has caused so much suffering that it is nearly universally despised.

Last year I decided to champion the lowly hackberry (Celtis). This year’s project: ragweed, a much tougher sell. Like most people you probably hate ragweed, but maybe I can help you admire just how well adapted it is for survival. And though it is the bane of so many people, it is extremely important for wildlife.

Why Is Giant Ragweed So Invasive?

Remember when Terence McKenna said plants invented animals to do their work?

Well, Giant Ragweed must have invented two powerful friends: Humans and Earthworms. The two organisms work in perfect harmony to ensure that Giant Ragweed can grow happily and abundantly ALL OVER THE PLACE.

Naturalized European earthworms (Lumbricus terrestris) think Giant Ragweed seeds are exceedingly delicious. They will tirelessly hunt the seeds down by smell. Earthworms won’t eat those seeds right away — they can’t. Instead, they cache the seeds deep underground and wait until the hulls decompose into a tasty slime. That might not sound appetizing to you but earthworms are picky eaters. Decomposed is the way they like things; in fact, they think the inner seed is disgusting and inedible so they just leave those bits behind. They kind of remind me of those people who need to cut the crusts off their bread.

This behaviour creates a handy seed bank in the soil. Those deposits will bide their time waiting for humans to disturb the earth. And humans love to dig. They dig into their gardens, they plow up fields and bulldoze construction sites. All that turned earth brings the banked seeds up to the proper germination depth. Next thing you know weeds seem to be growing everywhere.

Here’s a little movie that shows an earthworm gathering ragweed seeds. I haven’t decided if I find the accompanying music or the comments more amusing.

Giant Ragweed seed hulls are hard and need to be weathered away. So hard that the seeds can remain viable for several years. The embryo can also remain dormant. Those strategies give the plant many opportunities to wait out bad growing conditions.

Multiple Strategies Ensure Success

The plant is just as tough as the seeds. Shade. Sun. Who cares? And as long as it can get some moisture it seems to be able to grow in most soil types. Ragweed is native to continental North America and seems to grow pretty much everywhere with the possible exception of Nevada. And it seems to be spreading across the globe. I once saw a Giant Ragweed complaint that came from Korea.

Giant Ragweed plants don’t need pollinators, a breeze will do the trick.

And Giant Ragweed is one of the infamous resistant superweeds everyone was talking about awhile ago. Dosed with poison (even at 5x the recommended application) a genetically resistant plant will just grow extra shoots. At maturity that resistant plant will produce just as much leaf mass, pollen and seed as a plant left untouched.

What is it good for?

Yeah, I know. You probably channelled Henry Rollins’ emphatic: ABSOLUTELY NOTHING!

Ecology of Giant Ragweed

As an early succession plant, Giant Ragweed is important for stabilizing disturbed soil. It is one of those annuals that can grow quickly and abundantly. I have seen it grow more than ten feet tall in some places. The roots hold onto soil in danger of erosion. While alive the leaves offer shade and wildlife habitat. When they die, those leaves return organic material and nutrients to the soil. Giant Ragweed is sort of like a soil band-aid.

Because it is tall enough to stand above the snow pack Giant Ragweed is especially important as a winter food source in colder areas. Besides earthworms, many animals use it as a food source.

  • Insects: moth caterpillars, aphids, the bordered patch imago, hover flies and various grasshoppers. Honey bees love ragweed pollen.
  • Birds: the Greater Prairie Chicken, Dark-eyed Junco, Brown-headed Cowbird, Northern Bobwhite, Purple Finch, Mourning Dove, American Goldfinch and the Red-bellied Woodpecker
  • Mammals include the Eastern Cottontail, Meadow Vole, deer, horses, sheep and domesticated dogs. Long ago it was a source of food and medicine for humans. The oil content of the seeds compares to soy. The resin is anti-bacterial and anti-viral

The most interesting thing I learned about Giant Ragweed is that it is self limiting. When the plant dies the roots release a toxin that only seems to affect ragweed itself. When the concentration gets high enough the ragweed dies out making way for new plants to take its place. So really. Please keep the herbicide locked up. It really does make things worse.

Want to learn more? —

Worms and Ragweed

Eat the Weeds

As a Resistant Superweed

Ecology of

Lizard burrow in ragweed
Lizard burrow in ragweed patch
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28 thoughts on “Giant Ragweed

  1. Happily I am not alergic to ragweed. I must have missed the post you did about hackberry. I have a western hackberry growing in our parkway. It was on the list of tree choices provided by the city when the maple died. I wonder if I was the only person who voluntarily chose to have a hackberry planted in front of their house. It’s a great wildlife tree, I’m quite fond of it.

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    1. They are great wildlife trees but everyone around here speaks of them as weeds leaving me to sound like a James Bond super-villain as I shake my fist and yell, “Fools!” =)

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  2. This is a fantastic post. I loved the little video. You have added another dimension to my thinking about earthworms. I have always said there is a purpose for every part of creation, though we may have a hard time finding it. I am one of the fortunate people who are not allergic to ragweed, so I don’t have that inborn prejudice against it.

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    1. Thanks! I loved that little video, too. Pretty amusing. My husband and I had a very similar conversation recently: everything here co-evolved together. We can only guess at the complexity of how things are linked together. It takes a lot of hubris to decide some life forms don’t have the right to live with us.

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  3. Fascinating information–thanks! I don’t seem to recall seeing as much Giant Ragweed around here, but we definitely have Common Ragweed in great supply (either A. artemisiifolia and/or A. psilostachya). I wonder if the same is true for those species? I don’t seem to have Ragweed allergies. My allergies seem to be terrible when the corn tassles out in July, and then subside as the corn matures. Ragweed seems to be more of a problem for people in the late summer and fall. Allergies are miserable, no matter when they hit. Great post, to show the value of the plant in the ecosystem.

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    1. Thanks! I do not know much about the other ragweeds, unfortunately. Sorry to hear about your corn allergy. I never met an allergy I liked.

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  4. Fascinating about the earthworms and ragweed. Yes I am allergic to it and it used to badly affect my asthma so I do keep it out of my garden….love how it is self-limiting though.

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    1. We had some complaints one year from a community member living close to our wildlife habitat. She wanted us to remove the ragweed. And I really appreciated the despair she must have felt to see it growing thickly so close to her house. The leader of our group had some bad news for her: ragweed pollen is so tiny it can travel HUNDREDS of miles. We did agree to clear some of the patches as a good will gesture but now I see we shouldn’t have uprooted those plants: we should have cut them at the stem so the self-limiting toxin would have stayed in the soil.

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  5. You made a wonderful case for appreciating ragweed! But then I don’t think it’s very common here in New Zealand so we have less reason to hate it. It’s fascinating to learn that earthworms actually hunt and collect the seeds.

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  6. I so enjoy these posts. Love learning. I’m not familiar with ragweed .. and thankfully I don’t suffer pollen or plant allergies. With the exception of wandering jew :) I enjoyed the video. How amazing. I had no idea they would do this. I read somewhere else that they aren’t particularly interested in seeds (probably just as well) .. Where would be without those lovely slimeys.

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  7. Odd that your post is the second insistence this week in favor of ragweed. And also the music choice gives the worms a sort of Isadora Duncan choreography feel. Hoping you get some rain.

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    1. Oh thank you thank you. We all could use some rain and so back at you. Think the author and I should start a fan club for broadleaf weeds? hahaha about the music: I totally agree!

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  8. We have an abundance of ragweed growing here in the midwest. It looks very healthy.

    That Lumbricus terrestris video was amusing. I didn’t know they did that. I thought they just burrowed around to have a good time. You ever go fishing with them? We used to shove metal rods into the ground of our lawn and hook electrodes from an old telephone crank generator to them. A few cranks of the handle and those fellows would come up for easy picking. You can also drive a wooden stake into the ground and drag another piece of wood across the end to make it vibrate. That brings up the worms.

    The youtube note said the music was Chopin’s Mazurka Opus 7, No. 4 in A-flat. I liked it.

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    1. My husband and his friends just sneak behind my back to rob my compost bin for the wigglers. I will not tell them your (quite clever) trick for the earthworms though! hahahha I can just picture the destruction. I thought the busy pace of the music was pretty funny.

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  9. Ragweed is not a trigger for me (mine is oak) but I am very sympathetic to the plight. If ragweed is going to grow that well do you suppose we need to get busy finding our own use for the seed oil? Or is that me commodifying nature? I honestly get a little hung up over where the line falls between finding useful ways to co-exist, and using.

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    1. We can probably gather plants in away that doesn’t exploit them. I do remember wondering when I first moved here why someone hadn’t taken advantage of our excellent growing conditions for poison ivy and ragweed. I am just going to add it to my apocalypse/famine list for now. And because of its built in time limit, to not worry much if it ever seems to take over an area. We have some spots where it grows densely at WIllowbrook Reach. It might be worth documenting changes over time.

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  10. It hasn’ t reached the UK but with climate change there is a real danger that it will arrive, as it is spreading across Europe. One more misery for those of us who suffer from allergies. We have enough home grown ones.
    I loved your utube of the busy earthworm. Didn’ t you keep wanting to shout, ‘ You’ ve missed one!’.

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    1. I did hesitate. I know people who truly suffer and I didn’t want to make light of that. I am most curious about its self-limiting behaviour. I’d like to know if other early succession plants do that.

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