In the United States, loss of milkweed habitat is a major factor in the decline of Monarch butterfly numbers. Milkweed populations are decreasing primarily due to herbicide use. Also being blamed are climate change, disease and drought.
Why is this “weed” so important to the survival of a species? On their long, complex migration, female monarchs search for milkweed plants on which to lay their eggs. Monarch larvae (caterpillars) feed only on milkweed … with good reason.
Most milkweed varieties contain glycosides. When caterpillars feed on the leaves, they too become toxic, which continues into adult butterflies. Although not harmful to the Monarch, the toxins taste very unpleasant and cause stomach distress to their predators, such as birds. These predators then learn to avoid both the caterpillars and butterflies.
Milkweed is named for its milky, latex sap containing complex chemicals that are so unpalatable to most animals. There is a wide variation in toxin strength depending on the type of milkweed. The plants produce fleshy, pod-like fruit that splits open when mature, releasing seeds. Each of the many seeds is covered with downy, white hairs which aid in wind dispersal.
You can help the plight of the Monarch by planting milkweed and nectar plants. Include a couple of varieties of the 29 native Arizona milkweeds. Place about 18 inches apart in full sun; poor soil is preferred. Once established, they require little water and no fertilizer. Use no pesticides in the butterfly garden.
Planting a variety of nectar-rich flowering plants that bloom at different times will attract an assortment of diverse migrating butterflies. Include showy annuals like zinnias and passion flower with perennials such as salvia, coreopsis, and cone-flowers.
In your garden, add a water source for the butterflies such as a filled, large potting saucer or birdbath with a landing pad (river rock). Following are a few milkweed plants that grow successfully in our area.
Pineleaf Milkweed (Asclepias linaria), although requiring a bit more water, is probably everyone’s favorite because of its fern-like leaves and creamy flower clusters.
Desert Milkweed (Asclepias subulata) is also a host plant for Queen butterflies and the colorful Tarantula Hawk Wasp. It has gray-green, erect, nearly leafless stems, producing waxy, pale yellow flowers spring through fall.
Butterfly Weed (Asclepias tuberosa) has showy brilliant orange or yellow blossoms, is extremely heat-resistant, drought tolerant, and low maintenance.
If you do not want milkweed throughout your landscape, remove the seedpods before spreading with the wind. As an added bonus, the pods can make lasting additions to dried floral arrangements.
Watching caterpillars feasting on leaves, creating their chrysalises, then before your eyes turning into beautiful butterflies can be both entertaining and informative. Why not give it a try, while helping secure the future of Monarchs.
Mary Kidnocker is a University of Arizona Master Gardener who lives in the Green Valley area. Her articles are featured weekly.