Which Native Milkweeds Should You Plant for Monarch Butterflies?

Boyce Tankersley —  June 1, 2016 — 10 Comments

Want to help monarch butterflies? Be careful when selecting your milkweed. Not all plants that go by the common name of “milkweed” are the food that these butterflies need. 

Want to save the monarch butterfly? Plant milkweed. Pick up a free milkweed seedling at World Environment Day this Saturday, June 4.

Danaus plexippus (Monarch) egg on the underside of a leaf.

Danaus plexippus (Monarch) egg on the underside of a leaf. Photo by Bfpage [CC BY-SA 4.0], via Wikimedia Commons

Milkweed is both a food source and a host plant on which the monarch butterflies lay their eggs. Monarchs lay their eggs on the underside of the milkweed foliage.

After hatching, the larvae consume the foliage, which is high in cardiac glycosides—a poison that interferes with the heart functioning of vertebrates (animals with a skeleton). Butterflies are insects with an exoskeleton, and so are not affected by the toxin.

Within the Chicago region, the following milkweed species (Asclepias) are native:

  • Asclepias amplexicaulis is native to our prairies and is suitable for planting in sunny perennial flower gardens. The flowers are described as “eraser pink” in color and are fragrant (honey).
  • Asclepias exaltata is native to our woodlands and is suitable for planting in partially shaded gardens. The flowers are white and also fragrant.
  • Asclepias incarnata is native to both prairie and woodlands and can be planted in a variety of garden locations. The flowers are pink and fragrant. Gardeners may also be interested in three cultivars of this species:
    • ‘Cinderella’ has light and medium pink flowers
    • ‘Ice Ballet’ has white flowers
    • ‘Soulmate’ has medium and dark pink flowers
  • Asclepias tuberosa goes by the common name of Butterfly Weed. It features bright gold and orange flowers—and is fragrant. A native of sunny prairies, it also has cultivars that have been selected for specific colors:
    • ‘Hello Yellow’
    • ‘Western Gold Mix’
    • ‘Gay Butterflies’ (orange, red, yellow)
  • Asclepias purpurascens has fragrant pinkish-purple flowers and can tolerate both sun and shade locations in the home landscape.

Cultivars may be easier to find in your local garden center or nursery, but specialist nurseries do carry both potted plants as well as seeds.

Asclepias syriaca

Asclepias syriaca

Asclepias tuberosa

Asclepias tuberosa

Download the Chicago Botanic Garden Milkweed Map and take a tour of our native milkweeds.

The Bad Seeds

The bad actors, unfortunately, also go by the common name of milkweed, and are in the same plant family but a different genus: Cynanchum. Three species are reported in the upper Midwest and should not be planted by gardeners. All have fragrant flowers and wind-dispersed seeds:

  • Cynanchum louiseae goes by the name of Louise’s swallow wort, or milkweed. It is native to southeastern Europe.
  • Cynanchum louiseae goes by the name of European swallow wort or milkweed. It is native to southern Europe.
  • Cynanchum vincetoxicum goes by the name of white swallow wort or milkweed. It is native to Europe and Asia.

So, why will monarch larvae die on the wrong milkweed? 

Hmmm, perhaps an illustration. Both mango and poison ivy are in the same plant family (Anacardiaceae) and contain similar biologically active compounds. My daughter and I can’t get enough mango in our diet, but both break out in poison ivy rashes if we touch poison ivy plants. The compounds are similar but not exactly the same.

Likewise with the “bad” and “good” milkweeds: Both have fragrant flowers, the flower shapes are similar, the leaf shapes are similar, both have milky sap. But there is an insecticide compound in the “bad” milkweed in addition to the cardiac glycoside.

“Bad” milkweeds evolved in Europe, where there are no native monarch butterflies, but plenty of herbivores, both animal and insect. “Good” milkweeds evolved in North America in conjunction with monarch butterflies.

Monarch caterpillar

Monarch caterpillar

Somehow, the monarch larvae are able to ingest and retain cardiac glycosides in their tissues without dying. It is a very unique adaptation between these two species. If other species of butterflies were to lay their eggs on milkweed, the larvae would not survive. Each organism has these sorts of “monarch-like” relationships with other, sometimes drastically different organisms that give them a survival advantage. Monarchs just happen to be a wonderful example of mutualistic relationships.

Learn more:

The Monarch Joint Venture lists a number of national and regional partners; each of them will have information about monarch butterflies. The U.S. Fish and Wildlife Service, which is partnering with the National Wildlife Federation and National Fish and Wildlife Foundation, is also a source for information on milkweed and monarchs. Get free milkweed plants at monarchwatch.org.

Million Pollinator Garden Challenge

Add your garden to the Million Pollinator Gardens project this summer. Learn more at millionpollinatorgardens.org.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

Boyce Tankersley

Posts

Boyce Tankersley serves as director of living plant documentation at the Chicago Botanic Garden. His staff's responsibilities include maintaining records on over 2.5 million plants; verifying the accuracy of all plant nomenclature; labeling 9,500 taxa of permanent plants and 4,000 taxa of seasonal plants; mapping woody and perennial plants; and tracking the change in status of all accessioned plants from cradle to grave.

10 responses to Which Native Milkweeds Should You Plant for Monarch Butterflies?

  1. Thank you for this information and the pictures of the good milkweed – I didn’t know there was bad milkweed. So how do I tell the difference? How do I know if the milkweed I’ve allowed to grow for butterflies is good or bad?

    • The key to identifying the ‘bad’ milkweeds is the genus name. Good milkweeds are in the genus Asclepias.

      • Thank you, Mr. Tankersley. Is there an easy way for a common gardener – not a botanist – to ID the difference?

        • Boyce Tankersley June 1, 2016 at 3:02 pm

          This is a tough one because their are always exceptions to generalizations. In general, the bad characters are vines and have leaves that are cordate (heart shaped) with distinctively pointed tips to the leaves. In general, the good milkweeds are herbaceous perennials and do not twine around the stems of other plants.

  2. I don’t think you mentioned asclepias sullivantii. I think this is a native milkweed. Do monarch caterpillars not like this one?

  3. Paul Engbretson June 1, 2016 at 2:16 pm

    Good pic of asclepias syriaca, did I miss it’s mention in the text?

    • I am glad you like the picture. Another good native species that was not included in the descriptive text. Flora of North America identifies approximately 130 species in the USA and Canada.

  4. It’s best to stick to the native varieties, not cultivars

    • Boyce Tankersley June 9, 2016 at 6:19 am

      Just attended a really neat session focused on pollinator insects at the American Public Gardens Association annual meeting yesterday morning. Turns out this is a very complex question. Some of the cultivars turned out to be preferred by certain lepidopteran pollinators. When they researched the cultivars, it turned out they had not been hybridized, but merely selected from natural populations. The characteristics the insects favored were more flowers, higher sugar content, shorter floral tubes (easier to reach the nectar). Their research also suggested increased amino acids might also be a factor, but they have not followed up with another study yet. Amino acids are related to nutrition. What a wonderfully complex and interesting world we live in!

Leave a Reply

Text formatting is available via select HTML. <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

*