1. It is the stuff of life for monarch butterflies. Monarchs lay their eggs on milkweed, and milkweed leaves serve as nearly the sole food of monarch caterpillars. But many species benefit from the bounty of milkweed. Milkweed flowers produce nectar that other kinds of butterflies, honey bees, native bees and other pollinators enjoy. Hummingbirds line their nests with floss from milkweed seed pods.
2. It’s both medicine and poison. Milkweeds—there are more than 100 species—belong to the genus Asclepias, named after the Greek god of medicine and healing. Milkweeds have been used in medicine for thousands of years because their tissue contains cardiac glycosides, which increase the heart rate and in a purified form are useful in treating such conditions as cardiac arrhythmia and congestive heart failure. As a crude extract, cardiac glycosides are toxic and have been used as poison. Monarch larvae retain the toxins they consume in milkweed leaves and as butterflies remain toxic to predators.
3. Its presence is dwindling, along with the monarchs. The first decade of this century saw a 58 percent decline in milkweeds in the Midwest, according to a 2012 study—a time when we’ve also seen a whopping 81 percent decrease in monarch production. Factors often cited for milkweed’s decline include loss of habitat as grasslands and conservation reserves have been converted to farmland for corn and soybeans as well as increased use of herbicides on those crops.
4. There’s a growing movement to bring it back. Researchers at CALS and elsewhere have noted an increase in biodiversity, pollination and other ecosystem services that come from establishing or maintaining a mix of perennial native plants near cropland—and milkweed, they say, should be part of it. Vigorous efforts are taking place throughout the Midwest to plant large areas of milkweed along the monarchs’ migration path to Mexico, where they spend the winter.
5. Milkweed will enliven and beautify your garden—but keep your gloves on when handling. The toxins that protect the monarch can harm humans. Make sure the sap doesn’t get into your eyes, and if it does, seek medical attention as it can cause significant damage. While not all milkweeds are equally toxic and some kinds can be eaten, great care must be taken when selecting and preparing it.
Evelyn Howell is a professor of landscape architecture.