Tropical Milkweed: To Plant it or Not, it’s Not a Simple Question

Dara Satterfield SM

Dara Satterfield, PhD Candidate at the University of Georgia, is studying Monarch butterflies and OE. Courtesy photo

Graduate student Dara Satterfield came to town in late January for the second time in 12 months to take the pulse of the Monarch butterfly population at the San Antonio River Museum Reach Milkweed Patch.  There, dozens of Tropical milkweed plants play year round host to Monarch butterflies.   Satterfield works closely with local volunteers like Mary Kennedy and Mobi Warren of the Monarch Larvae Monitoring Project (MLMP), a citizen scientist program, to monitor milkweed patches far and wide for egg, caterpillar, chrysalis and butterfly action that might shed light on the state of the Monarch butterfly migration.

Monarch on Tropical Milkweed

Monarch butterflies LOVE Tropical milkweed. But is it appropriate to plant it? Photo by Monika Maeckle

Satterfield, like other scientists, believes the increased availability of  Asclepias curassavica, commonly known as Tropical milkweed, coupled with our warmer winters, may have an unhealthy impact on Monarch butterflies and their migration.   The science is undetermined on that question.

A native of  Marietta, Georgia, Satterfield attends the University of Georgia where she is a PhD candidate whose dissertation focuses on the relationship between migration and infectious disease in wildlife.  Monarchs are her species focus.  Satterfield works closely with Monarch scientist Dr. Sonia Altizer, the foremost expert in the country on Ophryocystis elektroscirrha, or OE. The unpronouceable protozoan disease infects Monarchs and other milkweed feeders, often resulting in butterfly crippling or death.

Dara Satterfield

Dara Satterfield checks Monarch butterflies at the San Antonio River Museum Reach Milkweed Patch for OE.           Photo by Monika Maeckle

As winters get warmer, Asclepias curassavica, the only milkweed species commercially available, is less likely to die back in winter. Some scientists hypothesize that A. curassavica entices Monarchs to forego migration and winter in the U.S. This could create an unhealthy hotbed of lingering OE spores for caterpillars and butterflies that remain in the local area.   Since the spores transfer from creature to creature via physical contact with each other or the plants on which they rest or eat, scientists worry that local OE-infested Monarchs will infect and breed with populations that are passing through, possibly jeopardizing the migration.

The situation exacerbates an already serious decline in the Monarch migration.  Drought, genetically modified crops, late summer wildfires, and generally inhospitable conditions pose multiple threats to Monarchs and their migration.   It’s likely that 2012 will be the worst year, numbers wise, in Monarch butterfly migration history since records have been kept.

“Monarchs are famous for this migration so when we see what appears to be a break in their migratory pattern, we want to know why and what the implications are,” said Satterfield.

OE Spores with Monarch Butterfly Scales

Eeeew! OE spores look like little footballs next to Monarch Butterfly Scales–photo courtesy of MLMP

But butterfly breeders and enthusiasts argue that OE is like staphylococcus–present in the general population and becoming a threat only under stressed circumstances. Organizations like the International Butterfly Breeders Association promote best practices for limiting OE in captive environments through education of its membership and seminars on managing and limiting its presence.  And yet others believe that OE is simply a part of the evolutionary cycle, killing those butterflies less fit than others.

For butterfly hobbyists and gardeners, the “curassavica question” presents a quandary:  should we be planting Tropical milkweed or not?

“This is a very sensitive subject in the Monarch world,”  said Satterfield.   “We just don’t have the data right now.” It will take three or four more years to complete Satterfield’s research.   She advises that natives are always better–which is true, IF you can find them and meet their persnickety growing needs.   Organizations like Monarch Watch and the Xerces Society‘s have launched milkweed restoration campaigns, but wide availability of native stock is still a dream.

If you DO plant curassavica, many scientists suggest cutting it to the ground in winter–unless yours is a research site like the Milkweed Patch on the San Antonio River Museum Reach.  Scientists encouraged the City of San Antonio and San Antonio River Authority to leave our milkweed patch alone as an experiment.   Interestingly, the San Antonio patch brags a lower incidence of OE (15%) than in other monitoring sites observed (47%) by the Monarch Larvae Monitoring Project.   The 47% figure is SIX TIMES the rate of OE in Monarchs that migrate to Mexico.

Satterfield suggested that a deluge of milkweed beetles at the Patch this winter decimated not only the foliage, but OE spores.  The hungry orange-and-black bugs pruned much of the diseased growth, creating a better balance for the butterflies. Apparently Mother Nature has her own way of managing the OE problem.

Milkweed beetles have defoliated the Milkweed Patch. But aren't they cute?

Mother Nature on the case: Milkweed beetles defoliated the Milkweed Patch last spring, cleaning out OE spores in the process. Photo by Monika Maeckle

“This may have removed any OE spores on the milkweed plants, which probably helped to keep the prevalence of OE low this year,” said Satterfield. She added that since our Milkweed Patch is further inland and enjoys cooler temperatures than coastal situations in Houston and Florida, the Monarch population was lower and perhaps more hearty.

In the meantime, gardeners are left to make their own calls.   Is it better to have a questionable milkweed source in your yard to provide Monarchs with nectar and host plant, or not?  

Let’s see: Tropical milkweed is easy to grow, widely available, prolific bloomer, favorite host plant for Monarchs and a great nectar source for all butterflies.   I know where I come down on that.   You’ll see Tropical milkweed in my yard.   But I’ll be sure to keep it out of wildscapes and ranch situations, and slash it to the ground in the winter.  

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36 thoughts on “Tropical Milkweed: To Plant it or Not, it’s Not a Simple Question

  1. I live in northern Florida and usually, the non-native milkweed is frozen to the ground each winter.
    The larvae of a tussock moth eats most of the new growth of A. curassavica in my yard each “spring” before Monarchs or Queens have a chance to oviposite. I wonder if this helps keep the spread of Ophryocystis elektroscirrha in check.
    A. humistrata grows along the roadside near my home but when I plant its seeds nothing comes up.

    • I just stick a cut stalk into a plastic water bottle for my monarchs to chomp on. After it is defoliators, I put it aside and in a very short time the stalks have strong roots. Just put them into a pot of soil and they will grow nicely.

      • How do you keep the cats from falling in the water and drowning?

        As to propagation, yes, just clip a stem with about 5 nodes, (maybe 5 inches), pull off all leaves except the top few, put it in a glass of distilled water. change the water weekly, in a month, you will have lots of white roots to plant in soil. I bring in a bunch of these cuttings before the first freeze to make lots of nice plants for the spring migration. cut off the top of the stem first, to have a branched plant.

        • I began raising Monarchs this year. Too keep them from drowning, I copied an idea to take a butter tub, fill with water, punch a hole in the top and stick the milkweed in the hole. No way cats can enter the small hole. The milkweed sends out roots and I pot up in soil. Big box stores spray most of their milkweed with pesticides, which will kill cats up to two weeks after you plant it so I root and plant my own pesticide free milkweed. Thrilled with my new hobby.

          • And I am thrilled to have gotten a reply. I hope you enjoy your hobby. I have asked about the yellow aphids and get no response. My bane this year is spider mites. They have taken over my plants, suck the juice out leaving mottled leaves. Does any1 reading this have any suggestions about combating spider mites? Lady bugs will eat monarch eggs, so that is not the answer

  2. Thank you for another well written, thought provoking article. The question of whether to plant tropical milkweed is difficult indeed. Here in South Carolina we are working with a nursery to raise indigenous milkweed but without success. So rather than have nothing, I will plant some tropical. Like you, I’ll cut it back.

  3. Pingback: The Milkweed & Monarch Situation – Links & Resources | The Roaming Naturalist

  4. Informative article, but no definitive answer. As far as common milkweed…although I have lots of seeds each year, I have not had any germinate that I have tried to grow. Instead I transplant them. Once established they send out lots of underground roots which produce new plants. They are invasive so it is a good idea to put them where they can spread without being a problem. I also have swamp milkweed which is native. At times I have supplemented with tropical milkweed in pots, but it is good to make those you purchase are free of herbicides…topical or systemic.

  5. Both common and swamp milkweed seeds need to be cold treated before planting. I collect fully ripe seed in the fall just before the pod opens on its own. Then lay out damp paper towels and scatter the seed on the towel so that none are touching each other. Roll the damp towel into a sausage and be sure to leave a little tag inside( written in ball point) with the date and variety of milkweed. Make several such rolls until all the seed is wrapped and put the sausages into a plastic bag, then refrigerate for the winter. I have read that 30 days is the minimum. I usually get about 90% germination starting the seed in little peat pots in a tray with clear plastic lid. Remove the lid when the seedlings are touching it. This year I am also trying storing the seed in a container of slightly damp sand, also in the refrigerator. Shake the container from time to time to scratch the seed. Do not let them freeze! Be ready to plant the seeds as soon as you remove them from cold storage. The damp towels may get a little moldy or discolored, but the seeds are usually fine.

    • Thank you for this ingenious and simple method of cold treatment! I’ve been procrastinating my seeds for months since I didn’t want to face the convoluted process of packing each type into separate baggies of moistened potting medium into the fridge.
      This is so much more straightforward and is a wonderful idea.

    • So now it is late June. The seeds I stored in the containers of damp sand germinated beautifully after I removed them from the frig. I stored seed of syrica, incarnata, and tuberosa in slightly dampened sand for at least 3 months, some a little longer. Be ready to get the seeds into the ground as soon as they are removed from the refrigerator because they will all sprout right in the container in a big jumbled mess if they stay in there at room temp for a week or so. The paper towel method described before also works fine. The seeds sprout in the towel and you have a risks of breaking root tips as you unroll it. Either way, seeds need a several month period of damp, cold storage (not freezing) in order to germinate in the spring.

    • I have had very good luck without cold storage. Last year, I just used starter trays and the seeds germinated in a few days with a very high success rate. Had so many plants, that I had to give many of them away. Began the process in late Jan. and actually had many bloom the first year/late summer

  6. Pingback: Is Tropical Milkweed Killing Monarch Butterflies- Grow or No?

  7. I live in South Florida.

    So try to understand, every American gardening guide/book/blog/website is pretty much geared around more temperate regions that have “seasons” such as “winter, summer, spring,” and so on as opposed to “hot season, hotter season, rainy season, post-rainy-hot season, and hurricane season” like we have here.

    So I’m going to plant curassavica without the slightest remorse whatsoever. The only question I have, is what to do with a plant that has been stripped bare to where the caterpillars are munching on bare stalks and there are still some fifteen to twenty that still need to eat?

    • I live in Palm Beach and I have had this same issue. This year I am trying to have 3 different sets of milkweed at 3 different stages, blooming, partially eaten, and stripped bare. Hopefully this rotation will bring success, if not I will just purchase more plants. Best wishes. BTW I have had success with rooting cuttings in water, try it!

  8. Pingback: Is Tropical Milkweed Killing Monarch Butterflies- Grow or No?

  9. Pingback: Asclepias curassavica (Tropical Milkweed) | The Landscape of Us

  10. This is a great article and thank you for writing it. I wanted to make two comments. I’ve been associated with UGA since 1986 and we are very proud of our researchers.

    Please note that Asclepias tuberosa is widely available commercially and that native plants are not persnickity (sp). Asclepias tuberosa is no more difficult to grow than tropical milkweed.

    Thanks again for a great article.

  11. If you cut off the bare stems and stick them in the ground, most will grow new plants. for the poor starving cats left, maybe take them to a nursery selling milkweed and place them on the plants. They will eat nothing else. If you put those bare stems in water, roots should form, another way to propagate I hear, but I just stick them in dirt. I starved my first year’s cats by not having enough plants. So now I plant a LOT. Here in central Texas the tropical plants freeze in the winter, so I hope I needn’t worry about OE.

  12. I didn’t see the email notification till I hit submit, so this post says nothing new, just serves to subscribe me.

  13. Hi,

    I live on the north side of Houston (The Woodlands area) and plant natives and pollinator attracting plants in my garden. I purchased what I believe is A. currassavica and it’s proliferating nicely. We have property in Normangee in Leon County (post oak savannah) and I am wondering if it’d be detrimental if I spread some seeds there. We do not run cattle anymore and have 100 acres of pasture. Is this species a native and what are your thoughts on establishing a pocket of milkweed to help with the monarch migration path?

    Thanks for your help,
    Karen

  14. I am so glad to come across your article. I planted a few tropical milkweed plants this spring and have had great luck with the Monarch butterfly reproduction cycle. I adore the flowers because I think they are stunning and they are so easy to grow and propagate. I have read a few articles suggesting that growing tropical milkweed was bad for the Monarchs because of the fact that this milkweed lingers longer than it should, thus confusing the butterflies and promoting diseases that are detrimental to the Monarchs. Our juvenile Monarchs only lingered for less than a day before they took off and tropical milkweed dies back in Virginia in the winter. After reading your article, I feel more confident to continue growing tropical milkweed. As you said, it seems that if we make sure that there is no milkweed around when it starts to get cold, that would be a good solution (instead of not growing them at all). Thank you for your article. You can see what I have done at cedarmerefarm.blogspot.com/2014/09/they-are-here.html

    • Thank you for the thoughtful comment, Christa. Yes, some folks are purists, but climate is changing our world. Zones for plants and butterflies are moving north as things heat up. As long as you cut it to the ground, I think that should serve well until science directs us further. Thanks for writing. MM

      • Hi Monika, at your advice, I have moved 7 caterpillars into safety. I have set up my “condo” with 3 potted milkweed plants in a plastic container. Because my plants are tall, I am using a large piece of cheesecloth to cover the condo. I have 3 questions: (1) will the caterpillars stay in the condo until they become butterflies; (2) if yes, do I need to provide them a different plant or a hard top so they can go into their chrysalis phase; (3) if they need to leave the condo in order to go into the chrysalis phase, how do I know when it’s time and where do I take them to? Thanks, Christa

        • Do you mind if I reply also? I am wondering if cheesecloth holes might be too big to keep predators out. Yes you hope they stay in till they become butterflies, if they don’t escape through the holes. They will attach to the cheesecloth. I hope they get enough circulation in the plastic box. Please keep us posted. Another thing, in the spring I put my enclosure in the sun because the plants don’t do that well in shade. The cats did not like that. Instead of the top of the enclosure, they made their chrysalis along the bottom of the pot. So now I have 8 new cats back under the porch overhand.

  15. Christa, just went to your address above, it says page does not exist, but when I clicked on “home” it came up. There was no way to leave comments, so I am back here. Your pictures are lovely, I am so impressed. Would love to hear your plastic box results, hope Monika does not mind if I leave my email, john.ruth.o1@gmail.com. I am in Georgetown, Texas

    • Hi Ruth, thank you for your suggestions and comments. I want to make sure I am helping rather than hurting the caterpillars. If you want to check my post again, try this and see if it works better: cedarmerefarm.blogspot.com

  16. I live in Santa Cruz CA, one of the monarch’s overwintering sites. What about planting tropical milkweed here? The monarchs would be here anyway so it doesn’t seem like it would be interfering with migration patterns but maybe there are other concerns. I’d welcome any information on this!

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