Monarchs and Milkweed

The 2020 count of overwintering monarch butterflies shows a decline from the previous year.  If you are concerned about the plight of the monarch, avoid using pesticides on your lawn and garden, and consider planting milkweed species native to the area where you live.

What's so special about milkweed? Milkweed is the sole host plant of the monarch butterfly. Monarchs lay eggs specifically on milkweed, the eggs hatch into caterpillars and the caterpillars eat the foliage. The leaves contain cardiac glycosides, compounds that affect heart function, making them toxic to most species of birds and mammals. By ingesting the leaves, monarch larvae become toxic and predators avoid them. 

Milkweed comes from the genus Asclepias, which is derived from the name Asklepios, the Greek god of medicine and healing. American Indians and settlers used the roots of this plant for treating respiratory illnesses and other ailments.  Asclepias consists of 130 species. Of these, 11 varieties are native or naturalized in Pennsylvania. The three most common species in our region are common milkweed (Asclepias syriaca), butterflyweed (Asclepias tuberosa), and swamp milkweed (Asclepias incarnata).

Common Milkweed (Asclepias syriaca)

Common milkweed is the most well-known species of milkweed native to North America. It thrives in full sun to partial shade in average to well-drained soils, and is commonly found in pastures, field edges and along roadsides. Spreading by underground rhizomes, makes this plant a good choice for erosion control. Its height can range anywhere from four to six feet. It has a short bloom period, from June to August, when it bears large clusters of fragrant pink flowers in spherical umbels atop the plant.  The ovate leaves are approximately six inches long and are borne on a single stalk. The undersides of the leaves are covered with short woolly hairs.

Butterflyweed (Asclepias tuberosa)

Butterflyweed favors full sun in dry to medium soil. It is a hardy, drought-tolerant species reaching one to three feet in height with a spread of one to two feet. The bloom period ranges from late summer to fall. The vibrant orange to slightly yellow flowers are an easy way to identify this milkweed. Unlike the majority of milkweeds, the sap of this species is not milky. It blends well in a perennial garden because of its clump-forming habit and height.

Butterflyweed. Photo credit: Bonnie Kaushik, Penn State Master Gardener Jefferson County

Swamp Milkweed (Asclepias incarnata)

As the common name suggests, swamp milkweed grows best in wet soil with full sun or partial shade. It can reach a height of four to five feet and should be spaced two to three feet apart. The narrow, smooth leaves are, lance-shaped and 3 to 6 inches long. Swamp milkweed has a long summer bloom period and flowers can range from mauve-pink to purple. Five tiny delicate petals are crowned with five nectar cups that are crucial in its intricate pollination. This species of milkweed is a great choice for wetland mitigation.

Propagation

Many species of milkweed are quite easy to grow from seed. Head outside in the autumn, or even in the early winter, and sprinkle the seeds around the garden. Burying the seeds can reduce germination rates since milkweed seeds need light to germinate. Just drop the seeds in the garden and press them down with your hand. Once you've sprinkled the seeds over the soil there's nothing else to do but wait. In spring, they'll germinate and begin to grow. Once the seedlings are a few inches tall, you can transplant them to different areas of  the garden. Be sure the new plants stay well-watered until they're established. Milkweeds are hardy plants that will survive with very little care.