Pollinator populations are in trouble for a lot of reasons. Loss and degradation of habitat, pesticides, and diseases are all major contributors. However, at least in the Central United States, much of the pollinator decline can be tied to spiny pink/purple-flowered plants and the way humans react to them.
Tall thistle, a native annual wildflower, is a big favorite among pollinator insects. However, it is seen by many people as a weed that needs to be eliminated from the earth.
On the face of it, thistles seem like they’d be pretty well-liked. Thistle seeds are a major food source for birds and other wildlife, as well as for a variety of invertebrates. The abundant nectar and pollen found in thistle flowers make them one of the most popular plants among both pollinator and non-pollinator invertebrates. As if that wasn’t enough, most thistles have large and/or abundant blossoms, which you’d think would make them very attractive to people. Sure, they’ve got spines, but so do cacti, yucca, and many other plants gardeners love to landscape with. So why do we hate thistles so much?
The cultural dislike of thistles is not at all a new phenomenon; references to the unpopularity of thistles can be found at least as far back as the Book of Genesis in the Bible. There, thistles are mentioned when God curses Adam after he eats the forbidden fruit. Genesis 3:17-18 – “Cursed is the ground because of you… Both thorns and thistles it shall grow for you…” Clearly, if God includes thistles as part of His curse on all humanity, they are not a crowd favorite.
Regardless of why thistles are so widely disliked, our contempt for them causes serious problems for pollinators. This happens in two ways: 1) direct destruction of an important floral resource for pollinators, and 2) major side effects associated with #1.
Because thistles are so important to pollinators, our compulsion to destroy them is a major problem. Sure, some thistle species are invasive and can cause enough ecological damage that their control is warranted. Most thistle species, however, are targeted for destruction purely because they are thistles. Many of those are native wildflower species and are not at all aggressive or problematic. Regardless, there are few places where thistles are tolerated, let alone encouraged. The result is the loss of a big source of food for many pollinators.
Musk thistles and regal fritillaries. Musk thistles are designated as noxious weeds and we are legally obligated to eradicate them.) The Nature Conservancy’s Platte River Prairies, Nebraska.
While the loss of thistles themselves is a big problem for pollinators, the methods we use to eliminate them can have much bigger impacts. If we were content to dig thistles out of the ground one by one, things wouldn’t be so bad. Of course, that’s not always feasible – some perennial species such as Canada thistle are rhizomatous and can’t be killed by digging. Herbicide use is the other available option. Spot spraying individual plants or clumps can be relatively innocuous, but only if the person spraying is judicious and selective about what they spray.
However, working thistles one by one takes a lot of time, and just because we hate thistles doesn’t mean we want to spend a lot of time getting rid of them. Broadcast herbicide spraying, by airplane or boom sprayer, can kill lots of thistles in very short order. It’s a great way to get rid of all those unsightly pink flowers in one fell swoop…at least for that season. Unfortunately, broadcast spraying also kills a wide array of other wildflowers, and most of those never recover (the ones that do are the ones we tend to like least – like ragweeds).
The grand irony is that because broadcast spraying kills so many non-target plant species, the spaces left open by those dead wildflowers are usually colonized by thistles. Thus, while broadcast spraying is quick, it tends to perpetuate thistle populations by destroying their competitors. (Also, most large thistle populations are there because of chronic overgrazing or some other major disturbance that weakens perennial vegetation and creates space for thistles to grow. Broadcast spraying doesn’t address those underlying issues.) Oh, and by the way, killing off all the wildflowers in a pasture or roadside also wipes out the pollinators that depend upon them for food.
Our cultural dislike of thistles leads us to kill off as many as we can each year. Since thistles are a major food source for pollinators, that’s grave news for pollinator conservation. Our desire for more “efficient” ways to kill thistles has led to even worse news, however – the loss of plant diversity across millions of acres. Since plant diversity sustains pollinators by providing varied and consistent food through the season, losing that diversity at a large scale is devastating. We can rebuild some of what we’ve lost through restoration, and we can save what’s left, but only if we change the way we think about thistles. We’d better hurry; pollinator declines are not slowing down.
I think we need a thistle fan club. Who’s with me?? Let’s do this thing. I’ve come up with a basic logo and tag line (below) to get us started. Click here to get an easily printable version you can hang on your office door or tape to your car window. It’ll be a great conversation starter! In fact, let’s have fun with this. If you feel like it, take a picture of how you displayed the logo and put it on your favorite social media with the hashtag #thistlehelp. Not a social media person? Feel free to email me a photo – maybe I’ll collect some of them and use them in a future post. If you email me, please keep the file size below 1 mb… Use this email address: chelzer(at)tnc.org.
The bees and butterflies of the world are depending on you. This is going to sweep the nation, you’ll see!
The Prairie Ecologist 
Chris, There’s been a thistle fan club since the 1200’s. It’s called Scottland! Not kidding: the thistle is our emblem and comes with some good stories.
Google thistle and Scotland or go to
scotshistoryonlie.co.uk or scottish-at-heart.com
Marilyn McNabb, who has spent untold hour digging young thistles, one by one, in March, April and May in Nebraska fields.
Heehee. Love it. Hey Chris – any way that could be a bumper sticker? I’d like one for my car.
Print out the photo and paste to your bumper… ;)
Good stuff!
Love it! This actually made me feel good about all the thistles in my yard; I need to make a sign to hang on my mailbox to ward off the township officials!
Now follow up with a simple picture collection of good thistle’s for we thistle eliterate common folk!
Exactly…like many of the Apiaceae family, thistles can be hard to id (especially without gloves, lol).
Yes! Great bumpersticker!
My friend has an outdoor sign on her “beach home” naming it THISTLE DEW.. another play on words for your consideration. And yes, any “good” variety to plant in Florida?
In Indiana it is unlawful to let thistles bloom and go to seed. But no one pays attention any more. Years ago farmers were heavily fined if “caught”. Now they no longer mow them down, just let them go and take over, but then farmers don’t do a lot of good things to show respect for the soil, nature or neighbors growing concerns. So sad. It’s like people just expect bad care doesn’t matter. So wrong.
Nancy, I’m an Indiana lawyer with lots and lots of thistle on our NW Indiana farm. To the best of my knowledge the only thistle defined as a detrimental plant in Indiana is Cirsium arvense, the non-native and invasive ‘Canada Thistle’. See Ind. Code 15-16-8-1. Native thistles, like Cirsium discolor, and even problematic ones like bull thistle (C. vulgare) are not regulated as far as I know. I agree that controlling C. arvense is worthwhile, but the native thistles are important components of the ecosystem, even if they are a bit prickly.
I know that Cirsium arvense is out competed over time by tougher-long lived prairie species. However, I am still going to pull this, and other non-native thistles, out of the ground when I find them. They compete with the natives for resources. Also, I don’t like getting poked by their needles when removing other faster growing weedy species from new plantings.
There are a number of native thistles that are not only great species, but are actually very rare and protected. The problem is the people who are paid to spray weeds are mostly not capable of telling the difference. After seeing the damage that has occurred to native communities and plantings from spraying to control invasive or “noxious” species I have become rather disenfranchised with allowing people to spray herbicide on any natural area. The problem is not herbicide; it is the carelessness of most applicators. It is just too risky to give most people such a powerful tool for killing vegetation in diverse natural areas and restorations. The licensing process to apply herbicide in my state, Illinois, tests for about everything except for a person’s ability to identify plants and their knowledge of application techniques to avoid damage to desirable vegetation. It is amazing how quickly extensive and costly damage can be done by people improperly applying herbicide. Even worse is that our tax dollars are often what is funding these destructive actions.
Sounds like better standards, minimum qualifications, and contract specifications are needed, not an outright ban.
I do not disagree with the use of herbicides, just spraying them in natural areas. The benefit of controlling the invasive species rarely seems to justify the damage that occurs. This is true even with the best applicators. In contrast, I have never had a concern when applicators paint herbicide onto bark or cut stems. This eliminates the risks associated with spray drift. Also, adding the additional step of cutting the stem helps reduce the chance of accidentally applying herbicide to a desired species.
As the caretaker of the environmental Nature center here on the Wasipinicion river I have tried to manage the thistles. This year I did not mow any to speak of except the Musk. Last year when tagging monarchs we found most of the few we had on tall thistles. Besides our state bird here in Iowa needs them too. I am all with you. I am seeing so many more monarchs this year and they have lots of tall thistles to feed on. thanks for the post.
I am with you all the way! Besides they are pretty and I only have a few rough blazing star plants and I need my purple/red fix in the area!
Good stuff. Out here in California, native Cirsium thistles are an important part of the summer flora that sustains bees, butterflies and birds. I grow the stunning, bright red Venus Thistle, Cirsium occidentalis var. venustum in my backyard, and the hummingbirds adore it. But I can also tell you a story about a ranger that dug up an entire patch of an endangered native thistle species, thinking he was helping out the local restoration efforts. So, while a thistle by any other name might still smell as sweet, it definitely helps to know which is which!
Great informational blog. Education, Education, Education…I have heard land manager biologists comment they did not want any thistle on any of the properties they manage- and we have native thistle in our area just like most everyone else.
Chris – I’m one of those people
who has continually tried to eradicate thistles from my tree farm. Now I plan to let most of them grow, except for musk thistle.
Way to go Dennis!!
This is probably one of my favorite articles! We have a lot of education to do as weed superintendents. It is hard to get people to understand that not all thistles are bad. Thanks Chris!
It’s State law here in Wisconsin to control the non-native Canada thistle. It is not enforced to my knowledge. Most biennial thistle species around the state are from the non-native Carduus genus. It is hard to find any native Cirsium thistles. In the lands that I manage, I only control Canada thistle. I don’t bother managing any of the non-native biennial thistles as they are quickly outcompeted by a healthy prairie. Unfortunately, many of the lovely native biennial thistles are outcompeted as well. I suspect this is one advantage of livestock grazing as it keeps creating the disturbance needed for native biennial thistles.
Chris, if you happen to have any quantitative information on the decline of pollinators at your fingertips, would you mind sharing?
Thanks, David
Love the logo and tag line. I plan to pass this along via Facebook to my plant nerd buddies with the underlying intention that others will see it and ask about it.
Just want to leave this unfortunate picture with you. Burdock seed-heads (not the flowers) can trap small birds and bats. Birds include American Goldfinch and the Kinglet group of birds (red-polled, etc.). Since Burdock is becoming so popular as a miracle health aid, it would be good to come up with a sticker (lol) to show the dangers of leaving burdock seed heads in the fields and gardens: (if you google Goldfinch caught in Burdock several articles will come up, too, including those from Canada regarding bats and Kinglets.)
http://marieread.photoshelter.com/image?&_bqG=22&_bqH=eJxtUF1LAzEQ_DW9N.HEVo9CHnLZ9VjaJJqPk.tLkGvFgnigtoK_3uxR9LAGMpmZzSTZ7C8.j_2xdvcHv6kGrcOqavvrr02_08uranlZljwzUgKvRDO8bJ_2r_1zQcmDDDhb1FrPFiAmBgAbABOry4NNXrONf6N4HsX_o4pCN14WcpmJstEE1yXylqV1hCbXyBqW5JPDNUqPcJJ3U.2tC8JJsyrG_pI0ID4yjx5dIhCRe384bJu5Km.GOT.gJReiXCfZoFEdbyqSqhPlg3P0ROMPdbe_VDOVKoj33eNb_sN2TDcjKsZvPIJyRw–&GI_ID=
Wow, thanks for this! Learn something every day. Found the paper, for those interested. https://www.researchgate.net/profile/Todd_Underwood2/publication/286179139_Bird_behaviour_on_and_entanglement_in_invasive_burdock_Arctium_spp_plants_in_Winnipeg_Manitoba/links/59e4f14b458515250246ebd7/Bird-behaviour-on-and-entanglement-in-invasive-burdock-Arctium-spp-plants-in-Winnipeg-Manitoba.pdf
Sorry, I mean “Ruby Crowned Kinglet” in the above comment.
I have a small native garden on a piece of land that is a nursery of sorts for some native plants, mostly wild canada rye, common milkweed, and boneset. The canada thistle really has taken hold of certain areas. I pull lots it out by hand. It sounds like the natives will slowly push out the thistle, or at least contain it. I look forward to seeing how this plays out over time…
We need to learn which thistles are the native ones, and which are not as aggressive, so we can feel comfortable letting those grow. Thanks for the information.
I am with you 100%. Not a good idea to endorse thistles without making this important distinction very clear.
Great post! Even worse than herbicides (at least for native thistles) has been the use of biocontrols agents…many of which have been very indiscriminate and damaging to native thistles. For instance there are at least 4 formerly-promoted biocontrols contributing to the decline of the federally listed thistle, Cirsium pitcheri (Pitchers or dune thistle)…which is also a key pollinator resource on Great Lakes dunes.
Native Plant Society of New Mexico has a free thistle identification booklet to help distinguish beneficial native thistles from noxious non-native thistles at http://www.npsnm.org. Other states should do the same.
Hello. Great article. I agree. I wrote a similar treatise on Mullein, published in Summer issue of Small Farmers Journal. “Mullein: Friend To All”. It would be interesting to collaborate with
Earth justice, NRDC, Center for Bio Diversity…
for seed ball making events with a campaign
To de-vilianize native indigenous plants listed
On the usual “noxious” list. Call if interested?
Wish there were better thistle ID keys available! I have a little (tiny) field in the Appalachian Mtns VA. When I first moved here I found a seemingly huge number of butterflies were attracted to what was growing in the field…thistle. Now, initially I guessed that it was a field of Cirsium arvense and I went about trying to eradicate the thistle. I learned that it cannot tolerate shade so I thought if I could kill most of it and fill the space with other plants I’d win! Five years later and considerably wiser (I think), I have discovered that the thistle probably wasn’t all C. arvense but that C. discolor was also present. Thankfully my attempt at eradication was far from successful! I have also discovered that the local universities have released a number of insects (bio-controls) to reduce the C. arvense population and unfortunately these are not species specific so just about every thistle plant I examine is loaded with weevils. I believe these weevils attack the flower buds, thus reducing the number of thistle flowers available for pollinators.
My problem is I’m trying to figure out if I’m looking at a patch of C. discolor or C. discolor and C. arvense. I know that most of the plants are C. discolor because they have white matting on the backs of the leaves but I didn’t think that pasture thistle could form a pseudo-colony, i.e. there aren’t branching taproots but the plants are numerous in a small area so it resembles a field of C. arvense. ….I thought C. discolor was supposed to behave more like dandelions, one here, one there etc. If I am looking at a patch of both species will the C. discolor eventually outcompete C. arvense despite the weevils?
We need to stop looking for simple answers (to kill or not to kill thistles), and insist on teaching people to be curious about plants (which sustain us in every possible way), and understand why protecting world-wide species diversity is important to global health. Then we need to study how the surrounding ecology that we are part of uses plants, and why it is important for people to key out plants, so that the thistles that make it not possible for a native thistle to live in its own home may be removed. Sigh, seems like a hard job, but this used to be a widespread hobby. How can a thistle issue compete with watching disasters unfold throughout the world on tiny glowing screens? Appreciate the discussion very much.
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A key from Missouri that may help.
Click to access ipm1015.pdf
Thanks for this, most helpful!
Very Clever! I’ll start integrating it – may I “steal” it? Full credit to you, of course!
please do! Thanks.
I love thistles nettles and any of the other so called weeds! They are here for a purpose. The fragrance they emit on a warm sunny day rivals anything I’ve ever smelled out of a high priced bottle of poison we’re so quick to adorn ourselves with! The world is a symphony and everything has a part to play . Particularly the invasive plants. It’s too bad some see themselves as St stewards of the land when in reality they are choosing the importance of one plant over another when all have a place and a use. When invasive plants lose their exceptional power of strength and resilience then one ought to be afraid for the health of all.
Of course plants are only doing what they are meant to do. Grow and multiply. Invasive plants do this in the absence of growth checks (like predators and diseases), and that means they quickly overwhelm the native plants that are checked by their native predators, so there is a man-made dis-balance there.
People who defend invasive plants present an active threat to native plant communities everywhere (and an active force towards less planetary diversity and extinction), because they do not understand the that many creatures depend on very specific plants to survive. Being opposed to the unchecked spread of invasive plants is not a “control freak” notion to try to control invasive plants (or a ploy to sell more chemicals as you may have been told on Facebook), but a grim battle to save species from being wiped out by them.
We have to do a better job of teaching the importance of ecological relationships. There are a number of invasive species where these same species are gobbling up ground all over the world. They are highly adaptable, and in some cases are noxious to native animals and humans. By mixing and stirring the planet’s species, we are setting up a situation that the biggest and baddest will survive…and those are plants that stand up to us quite well, not useful for medicines, or palatable, competing with our crops, and often creating health hazards of various kinds. Ever been burned by Giant Hogweed? Gotten lyme from escaped ornamental shrubs? Ever had your skin torn apart by Rosa multiflora, or watched starving deer wander the streets in the winter because they could neither hide nor dig up food from resting places choked with it? Ever seen your property value plummet with Japanese knotweed? Or see the tree seedlings in your woodlot be engulfed by plants that shade them out completely? Or had the grass meadows of your National Park become forests on one kind of tree?
We already played “St stewards of the land” when we introduced all those species. No, those plants are not “here for a purpose”, we are the ones who brought them here disrupting the way nature ordinarily works. What we are trying to do now is to minimize the damage already done in our ignorance.
As a further comment I believe there are no such things as “weeds”. The needs of the earth an it’s inhabitants dictate the movement of what some call “invasive plants” . Again I believe there is no such thing only plants doing what they are meant to do.
Shirley, you’re certainly entitled to your opinion, but I have to say I see things differently. Not all weeds are invasives – some are just plants that have characteristics we don’t care for – that’s subjective. But there are truly invasive species (plants and animals). Many of us define those invasives as species that disrupt and weaken the diversity and health of natural systems. For example, in our prairies, smooth brome is an invasive grass that, without active management against it, can essentially turn a diverse native prairie into a near monoculture that supports a mere fraction of the animals it previously did. Reed canarygrass can do the same with wet meadows. Now, in order to buy my argument, you’d also have to agree that natural systems like prairies require human intervention in order to survive and thrive. That can be difficult for some, but you might be interested in a post I wrote on the subject a few years ago. https://prairieecologist.com/2011/06/05/the-myth-of-self-sustaining-prairies/ Regardless, thanks for your comments, and all the best to you!
Chris – Your thoughts on Thistle both THRILL and challenge me. The notion of thistle being GOOD could be cause for an extra cup of coffee with a newspaper in the morning (and feel good about it) instead of mixing a load of herbicide and heading out to spot spray. Whatever would I have to talk about without thistle issues? Ah, yes. Wildlife and Pollinators! Truly a favored and happy topic!
I’ve just inherited my parents “retirement farm” (the pared-down version of the ranch they owned) after managing it for them for six years. It’s mostly CRP that’s quickly headed to one species. Canadian Thistle is a problem I’ve handled by spot spraying and MIGHT have reached “management” this year. Without broadcast spraying, we’ve used so little herbicide this year, the chemical company wonders if I’ve started doing business elsewhere. I’ve managed to encourage and spread beautiful quantities of Milk Weed (the Monarchs have been floating around this weekend) and some native grasses and forb are holding their own, but…
The research and planning for transforming the acres into the Pollinator program (through the FSA) when the contract ends (2020) has begun. Given six years of sitting on the ATV with a hand sprayer using GPS to map the trouble spots, I’m loosing sleep wondering what’ll happen when we start from a blank slate to re-plant. Do we spray kill everything? The hours of protecting Milk Weed, Spiderwort, Wild Geranium, etc by covering with sheets while spot spraying those blasted Canada Thistle brings me to tears. Do we burn the chemically-killed remainder and use no-till planting? (DEFINITELY no till.) Do we convert the upwind half year one and the downwind the next season? I’m filled to the brim with anxiety and questions.
Yes, I’m working with the local experts – your expertise and thoughts are welcome to join their voices. Thanks so much.
PS: The Thistle sticker really needs to be firmly attached to the vehicle. Neighbors will flock to begin THAT conversation!
I am a (fairly new) beekeeper. I cultivated a patch of thistle – approx 200 sq ft. While there was a lot of pollinator activity, especially honey bee, in late spring/ early summer (Late May, June, early July), I see very minimal activity in late July and August. Many of the flowers have puffed white, but there still seemed to be an abundance of purple blooms. My understanding is thistle should continue to bloom thru September. Any idea why the thistle blooms appear to be less attractive now?
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Thanks, Chris. I love your posts and share them often with my gardening groups. I have downloaded the New Mexico PDF on Thistle identification from one of your respondents and have shared this thistle blog and the ID booklet with FB groups. We have lovely purple thistle growing further north of San Antonio, and some isolated purple patches growing on the riparian edge of the I.H. 410 corridor in SA. Love thistle! Also, persons in medieval to current have used thistle for spinning. I personally have not tried to spin thistle, but it has been done. The carder used in carding wool is Latin for carduus: thistle. The Teasel was the original carder (spiny top of plant used for separating wool). I captured an image a few years ago of a Hawk moth on a Texas thistle bloom, but do not know how to share my image here. Many uses for thistle.
Hello again. While doing some more research on thistles, I came across this page from Washington State: https://www.nwcb.wa.gov/washingtons-noxious-weed-laws I wrote to them and asked them to read your blog… ha, ha. Now I will probably receive a note from them telling me how bad thistles are. On this page they show a Canadian thistle brought to Washington by settlers in the 1800s that they are fighting hard to eradicate. Canada borders Washington, so what is the big deal? I don’t think thistles see geographic boundaries quite like we do.
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Thistles are beautiful as well! I can’t imagine digging them out or spraying chemicals! I hope your blog post promotes awareness! I will be posting for Earth Day on seeds and a great book I read called, Seeds.
I’m with you on Thistles 🐝🐞 🙏🐦 Definitely time to get a branch of the club going here in Cork ….mlove the poster …thanks for a great article ☺️ Trish
https://www.corkcity.ie › natu…PDF
Web results
Nature in the City a guide to Biodiversity in Cork City 👋🐝💮
Garedn issues and laws wanted!
I made n my own polinator graden praries in my back filed.., but want to add more and registered, mapped with pollinator groups like..National Wildlife Federation, Wild Ones, Pollinator program with exorcis, Monarch Joint Venture, Madison Pollinator Pathway, and some poeple think theprograms( advoicate some higher agency…) are fake…I was told to get them down also for jealuosy form laws of offroading, snowmobles -visa verses -revenge or hate ..for useing a mower to care for the garden and path made for monitoring it…and for nutureing the garden made!
I would like to see a law that says pollintaor/vegitable gardens in in the USA are protected in a alternitive haigher fines and working in garden protection, privacy law, kind of like hunters now have, since they are not state or federal gardens so we anyone enjoy life under safe and be protected if registerd , mapped, no unlawful activities or even when not registerd!
Other groups who do reverse conservation get don’t get ignored when they want sfatey for harassre or people intentionally agrivating you outside when working and we have planting tools also that are jsut as dangerous..don’t need to be hurt because of someone hoping to make you trip or fall or other stuff to get your attention!I belaive lots of people would be happey for something giving them the same attention oether activities get!