Are All Milkweeds Good For Monarchs?

There was an interesting article in the New York Times on Monday about Monarch butterflies and milkweed. The takeaway is that planting Tropical Milkweed (Asclepias currasavica) may do more harm than good, according to several researchers.

Tropical Milkweed. Photo from University of Florida.
Tropical Milkweed. Photo from University of Florida.

Milkweeds, of course, are the only plants that are eaten by the caterpillars of Monarch butterflies.Changes in farming practices have led to a huge decrease in the number of native milkweeds. This in turn has been perhaps the chief cause in the decline of the Monarchs. As a result, gardeners have been encouraged to plant more Milkweed – but not all Milkweeds are created equal.

Monarch butterflies
Monarch on Swamp Milkweed

The danger from Tropical Milkweed is two fold. First, the availability of Tropical Milkweed in the fall and winter may disrupt the migration behavior of Monarchs – so that they settle down and breed instead of continuing their journey to Mexico. This is more of an issue in the Southeast than the Midwest.


Second, there is some evidence that Monarchs feeding on Tropical Milkweed are more likely to be infected by a harmful parasites.

There is not unanimous agreement that Tropical Milkweed is a serious problem. Chip Taylor of Monarch Watch believes that the plant is probably not beneficial to Monarchs but is not likely to cause “immense harm”.

Swamp Milkweed
Swamp Milkweed.

I’ve grown Tropical Milkweed (which in Chicago is an annual) in containers and found it rather unsatisfactory. I much prefer perennial native Milkweeds such as Butterflyweed (Asclepias tuberosa) and Swamp Milkweed (Asclepias incarnata).

Butteflyweed prefers well-drained soil, while Swamp Milkweed (not surprisingly) likes moisture. In my opinion they are both much more attractive than Tropical Milkweed.

2014-08-01 08.53.13

Even if the evidence against Tropical Milkweed is not conclusive, it just makes sense to stick with the natives.

Do you grow Milkweeds in your garden? Which species do you like best?

47 Comments on “Are All Milkweeds Good For Monarchs?”

  1. I grow a variety of milkweed. They are all nice for different reasons. This article is just typical of the poor science reporting we keep seeing from the NY Times. One mention of the real problem is given (use of a certain herbicide) but the rest of the entire space goes to discussing a speculative bugaboo. The trigger for monarchs to fly is temperature and the appearance of nice winds that make flying easier — not the availability of food. Tropical MIlkweed is a favourite plant but it isn’t the only one you can find here in Texas this late in the year — all the others are still green, too. This article displaces blame onto gardeners instead of pointing out the obvious — that farmers use a herbicide that needs to be taken off the market.

    • I think you’re being a little too harsh on the author of this article. First of all, it’s not the same reporter who has written some of the egregious pieces the NYT has published in the past. But secondly, the article does not say that individual gardeners are at fault for the decline of Monarchs. The article notes the enormous decline in wild milkweed and adds this: “The loss coincided with the increased applications of the weedkiller Roundup on expanded plantings of corn and soybeans genetically altered to tolerate the herbicide.”

      And later she says this: “No one disputes that loss of milkweed habitat remains the Monarchs’ biggest threat.”

      You may be right about migration, but some credible academics seem to think there is enough evidence to investigate the possibility that Tropical Milkweed has impacted migration patterns. The author is clear that as of now this is just a theory. There does seem to be evidence that feeding on Tropical Milkweed increases parasitic infections.

      The article is really about an aspect of the effort by gardeners to aid Monarchs by planting milkweed. To me it seemed worthy of discussion.

      • Bad word choice on my part to say ‘blame.’ I should have said ‘guilt.’ Clearly, when people choose to grow native plants over introduced species it is a win for all. I guess my main objection is that I see the Times continuing to use the same tactic perfected by stage magicians : minimize the audience’s focus on the real issue by deflecting their attention to something trivial. The number of monarchs affected by people growing tropical milkweed just doesn’t rate when compared to the damage caused by agribusiness.

  2. I read your post with interest and the comment by Debra above; if what she says is true and I rather suppose it is; then gardeners rather than farmers are getting the blame, she also mentions the winds, maybe they are changing too with climate change again a man-made problem.

  3. Complicated problems rarely have simple answers. And while the article doesn’t explore every factor of migration and habitat destruction, I don’t believe it’s trying to “blame” gardeners. Rather, in an effort to help gardeners help Monarchs, it’s raising a question, supported by facts, that deserves further consideration. Isn’t that newsworthy?

  4. This message has been traveling around gardening circles in the SE for a while now. We are definitely encourage not to plant tropical milkweed but it is the most likely milkweed that is found in big box stores so of course people who have only heard the message “plant milkweed” think they are doing a good thing. Also, in the past I have found that tropical milkweed is preferred by monarchs over other milkweeds. I no longer plant this type of milkweed in our garden. We plant butterfly weed, swamp milkweed and common milkweed. That being said getting monarch butterflies to visit our gardens has been challenging the past few years anyway. This fall we had lots of them but the year before none…very much depends on how the winds blow year to year.

  5. I grow common milkweed, no tropicals. I had a lovely little circular planting area with pachysandra and the milkweed came in. I decided to just let it go and multiply as much as it wants. So, it is kind of unkept but it is way in the back of the property and I view it as my gift to nature. We don’t see Monarchs any more and it is a sad state of affairs in my opinion. 😦

  6. My property came with a 350′ long ditch filled with all kinds of native plants and even trees and I have started ‘ditch’ gardening and find the experience fascinating. I started growing swamp milkweed (Asclepias incarnata) and so far they’re doing fine but I have not seen a Monarch since I moved here in Atlantic Canada. We have a lot of Viceroy but they feed on willows and poplars. They look like Monarchs. My favorite milkweed is Asclepias quadrifolia (four-leaved milkweed). Its flowers are very delicate and graceful. I do not have the right condition here to grow it and I remember reading a few years back that it was listed here in Canada as an endangered plant.

  7. The native milkweed multiplies like crazy here, but we are not in the flight path of the monarchs so I guess the small patch of the tropical variety is doing no harm. We gardeners should maybe adopt the “first do no harm” motto of physicians to avoid courting disaster.

  8. We all of us have an effect on the environment – and those effects are so long-term as to be completely unpredictable. We just have to do what we do ‘mindfully’. I admire your post for its cool observation – that’s an amazing contribution that gardeners can make to these kinds of environmental issues/panics… Saying that, both monarchs and milkweed are ‘exotics’ here – but my garden might be poorer if I didn’t try out a few Asclepias spp (although I’ll never be lucky enough to see the monarchs!) A fascinating, thought-provoking debate, even if these are not ‘our’ environmental problems ..

  9. I haven’t grown milkweed yet but I want to. Like you, I’ve heard a couple of things about the different types. Also, it is on some western states ‘invasive’ list so I have wanted to make sure I am educated on the types before I plant. I really do want to add some though…

  10. Southern Meadows (blog) did a very similar piece last year after learning that monarchs were lingering too long in GA because of the tropical milkweed. I stopped growing it after reading her post. But when I did grow it, the monarchs loved it. I stick with the orange milkweed and its swampy cousin.

  11. First I just want to say that the photo of the monarch up there is amazing! This makes so much sense. I only grow the native milkweed…no tropicals here. I suppose I am a bit boring but I find a lot of beauty in plants that are meant to be here….guess the butterflies do too! Happy weekend to you!! Nicole

  12. It’s an interesting conundrum isn’t it? In the lack of any concrete evidence and detailed studies and where there’s no solid conclusion, I agree with your advice – it’s best to stick with the natives since they’ve obviously worked fine before, so should carry on working fine.

  13. Good post. I didn’t even know there was a tropical milkweed. I saw milkweed for the very first time this summer while biking down a trail in the middle of nowhere. Saw these massive plants with the most incredible scent. I had to pull over. When I looked the flowers seemed very recognizable, couldn’t believe what I was seeing. For some reason I thought milkweed was a small plant but these were 4 – 5 feet high. not only great for the butterflies but they are absolutely gorgeous, made me want to get out and plant some ASAP.

  14. I am a terrible person, I prefer the tropical. I find it easier to grow than our native A. tuberosa and A. incarnata, at least in my garden. There is also evidence that parasites are not an issue across the southeast, mainly extreme southeast.

  15. Very interesting, Jason. I always assumed that the common milkweed and the swamp milkweed were the best for Monarchs, but I didn’t know that the tropical plant could cause problems. I do think the tropical milkweed is pretty, so I was considering planting it next year. I didn’t have any success with my swamp milkweed seeds last year–long story–but I intend to try again next year, and I have a seedpod from a common milkweed I snatched from a nearby roadside. I hope by next summer to have more than just the butterfly weed here.

  16. I have planted butterflyweed on several occasions, but it has never survived in my garden. (I suspect my glacial sand is too well drained for it.) On the other hand, common milkweed (Asclepias syriaca) self-sows readily, and I always leave several plants in place on my back slope. Alas, in recent years, these have not hosted any monarch butterflies, just zillions of milkweed tussock moths (for which milkweed is also a host plant).

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