Selecting Appropriate Milkweed Species

More than 70 milkweed species are native throughout the United States and Canada, but less than half of these have been documented as suitable monarch larval hosts (Borders & Lee-Mäder, 2014). When trying to create monarch habitat, selecting region-specific milkweed species that can withstand environmental stresses and be used by monarch larvae is key. Otherwise, monarch butterflies may deposit their eggs on a milkweed species that cannot be consumed by the caterpillars, causing them to starve and eventually die. Milkweed genera that should be avoided include Apocynum, Cynachum, Funastrum and Matelea. The one exception to this is sand vine (C. leave), which can be fed on by monarch larvae (Bartholomew & Yeargan, 2001). 

“Milkweeds: A Conservation Practitioner’s Guide” from the Xerces Society provides a list of appropriate milkweed species, based on ecoregion, that are deemed suitable hosts for monarch butterflies. Alternatively, the website monarchmilkweedhabitat.com provides an interactive map that lists native milkweed species for each state based on information from the USDA Plants Database.

Seeding Vs. Plugging

Plugs of milkweed can be secured through programs like Monarch Watch. Golf courses can purchase milkweed in flats from this program, similar to how tomato plants are grown, or apply for free plant material as part of a habitat restoration program. To qualify for free milkweed plants, two acres of habitat is needed. Golf courses are eligible to apply for the program.

Alternatively, a golf course could easily create their own flats of milkweed by sowing seeds into small containers or flats. This a perfect project for facilities that have their own greenhouse. Establish plants during late winter and transplant in the spring once air temperatures consistently reach 65 to 75 degrees Fahrenheit. This method is a great way to give milkweed a head start over weed competition. Generally, milkweed plants will be ready for transplanting four to eight weeks after seeding.

Tips For Seeding

Tips For Plugging

Holes for plug plants can be dug with a basic hand trowel or small auger. To increase efficiency, dig all the holes at once in advance of planting. Milkweed plantings should be in small clusters of three to five individual milkweed plants. This will allow employees to more readily distinguish the milkweed from other look-alike plants they may want to remove. Monarch butterflies are also better able to locate clusters of plants compared to individual plants that are spread out. For the best results, position the clusters of milkweeds along the perimeters of naturalized areas so that the monarchs can easily find them and are able to avoid potential predators that may be more prevalent in dense cover. 
Planting plugs should occur as soon as possible during spring once the threat of frost has passed. Young milkweed plants will be susceptible to drought stress and will likely require supplemental irrigation every couple of days during the first four weeks after planting. Adding a little starter fertilizer is not required but can aid in development.

Management

Setting Realistic Expectations 

Transforming an existing site into a picturesque landscape of blooming wildflowers is going to be a slow process that requires patience. It is not uncommon for things to look somewhat ugly during the course of the first year. Milkweed plants will be puny and keeping the area free from weeds will require diligent hand work. Over the course of the first three years, the overall look of the area should dramatically improve while maintenance efforts will be simplified. Don’t let the temporary inconvenience deter you from the attractive and healthy landscape that can be achieved. Monarch butterflies and other pollinators are counting on you.

Thanks to Marcus Gray at Audubon International for providing valuable information and feedback on this article.    

References

Baker, A.M., and D.A. Potter. “Colonization and Usage of Eight Milkweed (Asclepias) Species by Monarch Butterfilies and Bees in Urban Garden Settings.” Journal of Insect Conservation, vol. 22, 2018a, pp. 405-418.

Baker, A.M, and D.A. Potter. “Japanese Beetles’ Feeding on Milkweed Flowers may Compromise Efforts to Restore Monarch Butterfly Habitat.” Nature, 14 August 2018, www.nature.com/articles/s41598-018-30731-z.

Bartel, R.A., et al. “Monarch Butterfly Migration and Parasite Transmission in Eastern North America.” Ecology, vol. 92, no. 2, 2001, pp. 342-351.

Borders, B., and E. Lee-Mäder. Milkweeds: A Conservation Practitioners Guide. Xerces Society for Invertebrate Conservation, 2014.

Fischer, S.J., et al. “Enhancing Monarch Butterfly Reproduction by Mowing Fields of Common Milkweed.” The American Midland Naturalist, vol. 173, no. 2, 2015, pp. 229-240.

Luna, T., and R.K. Dumroese. “Monarchs (Danaus plexippus) and Milkweeds (Asclepias species): The Current Situation and Methods for Propagating Milkweeds.” Native Plants, vol. 14, no. 1, 2013, pp. 5-15.

Pleasants, J.M., and K.S. Oberhauser. “Milkweed Loss in Agricultural Fields Because of Herbicide Use: Effect on the Monarch Butterfly Population.” Insect Conservation and Diversity, vol. 6, no. 2, 2012, pp. 135-144.

Thogmartin, W.E., R. Wiederholt, K. Oberhauser, R.G. Drum, J.E. Diffendorfer, S. Altizer, O.R. Taylor, J. Pleasants, D. Semmens, B. Semmens, R. Erickson, K. Libby, and L. Lopez-Hoffman.  “Monarch butterfly population decline in North America: identifying the threatening processes.” Royal Society Open Science, vol. 4, no. 9, 2017, pp. 1-16.