The Beautiful Reason You Should Plant Milkweed

A monarch butterfly feeds on Asclepias incarnata swamp milkweed. Mark Herreid/Shutterstock

Want to do your part to help reverse the dramatic decline in monarch butterflies? Now’s your chance: Plant milkweed.

Monarchs are dependent on milkweed, especially milkweeds in the genus Asclepias. Milkweed is the only plant on which monarchs will lay their eggs and on which monarch caterpillars will feed.

By starting milkweed from seed indoors or buying nursery seedlings for your early spring plantings, you can create "Monarch Waystations." Monarch Watch, an educational outreach program based at the University of Kansas that engages citizen scientists in large-scale research projects, believes Monarch Waystations are critical to helping monarch butterflies survive what is one of the most fascinating migrations in the natural world.

The spring migration begins in mid-March and extends from the monarch’s winter home in central Mexico as far as 2,500 miles north to breeding grounds in the eastern United States and Canada. The butterflies, which cannot survive freezing temperatures, return to the high-elevation Mexican forests in the fall.

“There are 73 species of milkweed in the United States,” said Chip Taylor, director of Monarch Watch. “Monarchs use about 30 of these as hosts. About four of these species – Asclepias incarnata (swamp milkweed), Asclepias syriaca (common milkweed), Asclepias tuberosa (butterfly weed) and Asclepias viridis (green antelope horn) – sustain 98 percent of the eastern population of monarchs.”

Unfortunately, habitats that support monarchs are becoming more and more scarce each year. Commercial and residential development, chemically intensive agriculture, and aggressive mowing and use of herbicides along roadsides continue to destroy many of the primary remaining habitats of milkweed — pastures, hayfields, edges of forests, grasslands, native prairies and natural spaces in urban areas.

To help sustain remaining habitats and to create new ones in places such as backyard gardens, school and hospital grounds, and office campuses, Monarch Watch accepts donations of milkweed seed from around the country. Monarch Watch has formed partnerships with nurseries that distribute milkweed in flats of 32 plants to areas from which the seeds originated. They also offer a free flat to schools and non-profits in the donor regions.

A regional list of states, and seed from milkweed species that has been donated by those states, is available at Schools and non-profits can learn how to obtain free flats here.

While Monarch Watch is eager to accept seed donations from all regions, they especially would like to receive seed (except for tropical milkweed seed) from the Southeast. “The Southeast – Florida, Alabama, Georgia and South Carolina – is a big hole in our operation right now,” Taylor said. “We need to get people in these states to donate seed.”

common milkweed
Common milkweed. Wikimedia Commons

Milkweed is easy to grow from seed or transplants. Just follow these general guidelines:

Choosing which milkweed to grow

Choosing which Asclepias to grow depends on whether you live east or west of the Rocky Mountains. The Rockies form a sort of dividing line for two populations of monarchs. The main population breeds east of the Rockies in the spring and summer. This group migrates to central Mexico in the fall where they spend the winter in the Transvolcanic Mountains in oyamel fir forests, which themselves are in decline. The western monarchs overwinter all along the California coast in up to 300 locations, using about 100-150 locations in any given year.

Good choices for Ascelpias east of the Rockies include common milkweed (A. syriaca), swamp milkweed (A. incarnata) and butterfly weed (A. tuberosa). Green antelope horn (Asclepias viridis) is recommended for the South Central region.

“Adult Monarchs are generalized flower visitors and will feed on a variety of nectar-producing plants,” Taylor said. East of the Rockies these include such nectar-producing plants as Indian blanket (Gaillardia pulchella), purple coneflower (Echinacea purpurea), Joe Pye weed (Eupatorium purpureum), scarlet sage (Salvia coccinea), Tithonia Torch, Mexican sunflower (Tithonia), and a zinnia-dahlia mix (Zinnia elegans).

Good choices for Ascelpias west of the Rockies include narrowleaf milkweed (Asclepias fascicularis), showy milkweed (Asclepias speciosa), swamp milkweed (A. incarnata) and butterfly weed (A. tuberosa).

To provide nectar for adult monarchs west of the Rockies, consider planting blue sage (Salvia farinacea), chia (Salvia columbariae), scarlet sage (S. coccinea), Tithonia torch, Mexican sunflower (Tithonia) and a zinnia-dahlia mix (Z. elegans)

Where to buy milkweed

Milkweed seeds and plants are available from mail order and local nurseries, especially those specializing in native plants, as well as from Monarch Watch.

Growing from seed

Starting milkweed seeds indoors works best because seeds sown indoors have higher germination rates than seeds placed directly in the garden. Seeds may require some cold stratification. Another advantage to starting seeds indoors is that well-rooted transplants have a better resistance to weather extremes and pests than seeds started outdoors.

When to plant

Plant seedlings in the garden when they are 3-6 inches high and after danger of frost has passed.

Where to plant

Most milkweed species will do best in the sunniest areas of your garden. A few species, such as A. purpurascens, appear to require partial shade.