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Minnesota gardeners are adding milkweeds to their landscapes to benefit native pollinators. Milkweeds are well known as a monarch butterfly host plant, but they provide several other ecosystem benefits that we will explore in this Hot Topic.
Learning Objectives
Learning Objectives
Understand key characteristics of the genus Asclepias
Analyze the role of milkweeds in the ecosystem
Examine the causes of milkweed decline
Identify uses for milkweeds in the garden
Common milkweed, Asclepias syriaca. Image credit: U.S. Fish and Wildlife Service Mountain-Prairie Unit
The Genus Asclepias: an Overview
The Genus Asclepias: an Overview
North American milkweeds are members of the genus Asclepias. Approximately 110 native species of Asclepias exist in North America, 16 of which are found in Minnesota. Swamp milkweed, common milkweed, whorled milkweed, butterfly milkweed and green comet milkweed are especially common in the state.
Most plants of this genus produce a milky white, sticky, latex sap that gives the plant its name. Milkweeds produce seed pods with tufted seeds that are wind-dispersed. They also produce toxins called cardenolides, which are steroids that can cause cardiac arrest if eaten by humans or other mammals.
Amongst plants, milkweeds have unique and elaborate flowers with an unusual pollination strategy. Milkweeds usually produce flowers in clusters called umbels. Umbels have multiple individual flowers on short stems coming from a single branch. A singular flower on a milkweed umbel has five nectar-containing hoods that surround a structure in the middle called the gynostegium. The gynostegium, a structure that is made of fused male and female parts of the flower, houses the plant’s pollen store. Unlike most plants, milkweeds don’t release individual pollen grains.
Instead, they package their pollen in wishbone-shaped sacs called pollinia (singular: pollinium). The pollinia are housed in a ring around the base of the gynostegium. Milkweed pollen therefore is not as accessible to pollinators as single-grain pollen may be on other plants.
If there is no pollen available, why would pollinators bother visiting milkweeds? Milkweed flowers produce a lot of nectar to attract pollinators. The flowers are very slippery, so when an insect visits the flower to drink nectar, they struggle to grasp a surface. As they struggle to hold on, their legs come into contact with small slits at the base of the gynostegium. These slits have specialized hairs that direct the leg upward to make contact with the pollinium. When the insect pulls free, the pollinium detaches from the flower and hangs off the insect’s leg.
When the insect lands on the next milkweed flower, its leg gets stuck again. When the insect pulls free, the pollinium detaches and slides into the slits at the bottom of the gynostegium, completing pollination. While this process benefits milkweed, the nectar comes with a cost to some insects. Smaller insects may not be strong enough to remove their legs from the slits, causing limb loss or death. Larger insects, like wasps, butterflies and bumblebees are usually safe. Despite the complexity of pollination, milkweeds continue. Fortunately, only one flower per umbel requires successful pollination to produce a seed pod.
A milkweed longhorn beetle (Tetraopes tetrophthalmus). Image credit: Anita Gould
Milkweeds in the Ecosystem
Milkweeds in the Ecosystem
Milkweeds are excellent pollinator plants. They are fragrant, full of nectar (but no accessible pollen) and attract a variety of bees, butterflies and other insects. Although milkweeds produce toxins, there are several insects that feed on their stems and leaves, including oleander aphids, milkweed longhorn beetles and large milkweed bugs. Many of the insects that feed on milkweed sequester milkweed's toxins to use for self-defense. The insects that feed on milkweed in turn support organisms further up the food chain, such as predatory insects (like lacewings and lady beetles), birds and snakes. Milkweed is part of a larger ecosystem that provides vital habitat for several key wildlife species.
Most famous of the milkweed feeders is the monarch butterfly, whose caterpillar feeds on milkweeds and sequesters its toxins. The U.S. Fish and Wildlife Service proposed that the monarch butterfly be listed as threatened under the Endangered Species Act in December 2024. Milkweeds are required host plants for monarch larvae; adult monarch butterflies only lay their eggs on milkweeds. The eggs hatch into caterpillars that feed exclusively on milkweeds. Monarch butterflies need milkweeds to complete their life cycles, and the decline of the monarch is closely tied to the decline of milkweeds across the midwestern United States.
Milkweeds were once prominent across the United States, especially the Midwest. They thrive in disturbed areas and were historically a common weed in agricultural fields. After the release of glyphosate-resistant crops in 1996, milkweed populations declined rapidly. Monarchs and milkweeds both began declining as they experienced habitat loss. This coincides with a global decline in insect populations, including bees and butterflies.
Milkweeds in the Garden
Milkweeds in the Garden
Planting milkweeds in your yard, gardens or landscapes is a great way to provide habitat for insects, including pollinators, and their predators. Milkweeds are low-input plants: they are drought-tolerant and require minimal fertilizing. Their drought tolerance makes them good choices for our landscapes that are likely to be affected by hotter, drier summers as we continue to be impacted by climate change.
Whorled milkweed (A. verticillata). Image credit: Dan Mullen.
There are milkweed species for most conditions in your yard. Swamp milkweed (A. incarnata) is an excellent choice for wet, sunny conditions, including swamps, as the name indicates. For dry, sunny conditions, butterfly milkweed (A. tuberosa), whorled milkweed (A. verticillata) and green comet milkweed (A. viridiflora) are good choices that are common in dry prairies. Common milkweed (A. syriaca) is the most versatile and is best at colonizing disturbed spots. However, since it spreads via rhizomes, it has the potential for aggressive, weedy spread.
Milkweeds are toxic to humans, pets and livestock. Contact with the sap may cause skin irritation, and consumption of any part of the plant can cause vomiting, weakness and muscle spasms. If you have curious humans, pets or livestock that may be tempted to eat milkweed, proceed with caution when adding it to your space.
Test Your Knowledge
Test Your Knowledge
Additional Resources
Additional Resources
Native milkweeds hub page from the Xerces Society
Milkweed FAQ from the Xerces Society
Common milkweed from University of Minnesota Extension
Year of the Asclepias news article from University of Minnesota Extension
Native Plants for Pollinators and Beneficial Insects: Great Lakes (eastern MN) from the Xerces Society
Native Plants for Pollinators and Beneficial Insects: Northern Plains (western MN) from the Xerces Society
Monarchs and Milkweeds youth curriculum from University of Minnesota Extension 4-H
References
References
Eldredge, E. 2015. Milkweed Pollination Biology. USDA NRCS Technical Note NV-58, Great Basin
Plant Materials Center, Fallon, NV.
Hopwood, Jennifer, et al. Roadside Habitat for Monarchs: Milkweeds of Iowa and Minnesota. Xerces Society.
Pleasants, John M, et al. “A Comparison of Summer, Fall and Winter Estimates of Monarch Population Size before and after Milkweed Eradication from Crop Fields in North America.” Insect Conservation and Diversity, vol. 17, no. 1, 9 Jan. 2024, pp. 51–64, https://doi.org/10.1111/icad.12687.
Puffer, Katie-Lyn. Teaching Monarch Conservation. 5 Feb. 2025.
Thogmartin, Wayne E., et al. “Monarch Butterfly Population Decline in North America: Identifying the Threatening Processes.” Royal Society Open Science, vol. 4, no. 9, 20 Sept. 2017, https://doi.org/10.1098/rsos.170760.
Zaya, David N., et al. “Long-Term Trends in Midwestern Milkweed Abundances and Their Relevance to Monarch Butterfly Declines.” BioScience, vol. 67, no. 4, 8 Mar. 2017, pp. 343–356, https://doi.org/10.1093/biosci/biw186
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