Want to attract Monarch butterflies?
There is growing interest among gardeners and environmentalists in the population decline of the Monarch butterfly (Danaus plexippus) and the role that milkweed plays in the Monarch's life cycle.
Many of us are interested in helping the Monarch but are leery of planting milk-“weed.” Here is general information on milkweeds as well as species-specific information to help you select the appropriate milkweed plants for your garden and support the Monarch butterfly population.
Milkweeds (Ascelpias spp.) are native perennials and are often considered a “weed” as the name suggests.
The plants in this genus are often found in old fields, pastures and along roadsides. There are more than 100 species throughout North America, of which five are found in Pennsylvania. Of these, the three most commonly encountered species in Butler County are common milkweed (A. syriaca), swamp milkweed (A. incarnata) and butterflyweed (A. tuberosa).
Wild milkweed populations, especially common milkweed, have declined significantly because of habitat loss and herbicide use.All milkweed species have fine leaf hairs and sap as defense mechanisms to deter animals and insects from eating the plant.Cardiac glycosides contained in the sap are also poisonous to humans and livestock.A number of insects tolerate the glycosides and store them in their bodies as a toxic defense against their own predators. Many of these insects are boldly colored and patterned to warn would-be predators that they don't taste good.The Monarch butterfly is probably the most famous of these insects. The butterfly uses this mechanism as a defense against birds that would feed on them or their caterpillar.The large milkweed bug (Oncopeltus fasciatus) can be found feeding on milkweed, and the red milkweed beetle (Tetraopes tetrophthalmus) prefers swamp milkweed.Despite being toxic, milkweeds are highly valuable not only as caterpillar hosts for the Monarch butterfly but as nectar sources for a myriad of flies, beetles, bees, wasps, butterflies and moths.
Common milkweed is probably the best known of the species found in Butler County, primarily for its association with the Monarch butterfly. However, more than 450 species of insects feed on some portion of the plant.Common milkweed grows to about 5 feet in height. Ball-shaped clusters of greenish pink to light rose or violet-pink flowers emit a strong, sweet scent, attractive to bees. Mature pods are about 4 inches long. When the pod splits open, it releases 50-100 seeds with a fluffy “parachute” that allows wind dispersal. Of the three species, common milkweed is the most aggressive and difficult to remove, so make an effort to plant it only in places where you can allow it to spread.Swamp milkweed also grows to 5 feet in height. Leaves are more slender and flowers bloom at the top of the plant as flat clusters of darker rose-purple blossoms. The seed pods are narrow. Swamp milkweed, as the name suggests, requires a moist habitat and is an excellent plant to add to a rain garden or damp site in your yard. This plant is a more cultivated alternative to common milkweed and also is attractive to egg-laying Monarchs.Butterflyweed is the least aggressive of the three species and the only one with clear sap. This plant grows to about 2 to 2½ feet in height, and because of its small stature, can be planted in a smaller garden space or a container. The flowers are produced as flat-topped clusters similar to swamp milkweed, but butterflyweed blossoms are bright orange to bright yellow in color. The seed pods are long and narrow.Milkweeds are best grown in full sun but will tolerate part shade. They do well in heavy clay soils and are deer resistant. Orange milkweed aphids (Aphis nerii) are common pests of milkweed plants. If you notice large concentrations of them, spray the plants with water.
Milkweed seeds require a period of cold in order to germinate. Spreading seeds on the top of bare soil in the fall will allow the winter temperatures and snowfall to do the work for you. Alternatively, seeds can be refrigerated for three months prior to planting or started in containers and placed outdoors in February. Buying seedlings or plants is a faster alternative.Once established, milkweeds spread by rhizomes and form colonies. Seed is spread via wind-dispersal. Harvest the seed pods before they open to control dispersion of the seeds to areas where you do not want it to grow. Divide plants and place in the ground by late fall, so they can develop enough root system to survive the winter.On occasion you may come across a colorful red and yellow milkweed, the tropical milkweed (A. curassavica) in nurseries or garden centers. Native to Mexico, Central and South America, it is sold because of its attractive bright flowers and as a Monarch nectar and host plant.Scientists studying Monarch butterflies have voiced concern over growing this species in the United States.In the southern and southeastern United States, this species can have leaves and flowering into late fall, and there is thought that it is causing Monarch to lay eggs outside of their breeding season, possibly delaying migration.In addition, there is discussion that tropical milkweed may also increase the rate in which Monarchs are infected by a parasite (Ophryocystis elektroscirrha). Here in the north, the plant would be grown as an annual; however, the origination of the plants would be from outside of our region and could contain the parasite.
The best practice is to plant the species native to our area despite the temptation of purchasing a colorful tropical species.Whatever space you have, soil type, moisture conditions, or color preference you may desire, there is a species of milkweed that can work well for you and help pollinators.So consider planting milkweed somewhere in your yard or even some butterfly weed in a container. The pollinators, especially the Monarch butterflies, will thank you.Penn State Extension offers additional information on growing milkweed at https://extension.psu.edu/monarchs-and-milkweed. If you have questions about Monarch butterflies, pollinators or growing milkweed, call the Butler County Master Gardener Garden Hotline at 724-287 4761, Ext. 7, or email the Master Gardeners at butlermg@psu.edu.Mary Alice Koeneke is a Penn State Extension Butler County Master Gardener.
