My first encounter with butterfly weed (Asclepias tuberosa) occurred while hiking through a meadow at Gifford Pinchot State Park in northern York County.
Mixed in with the native grasses were green, shrub-like plants, topped with brilliant, clustered, orange flowers. Many assorted pollinators were hungrily consuming the nectar, so remarkably in fact, that it attracted my attention, as well. Since becoming a Master Gardener, many native plants are more noticeable to me and this plant quickly became a “must-have” for my garden.
Identified as the 2017 Perennial Plant of the Year by the Perennial Plant Association, butterfly weed is known for its ability to support insects and birds and serves as the primary caterpillar food for the monarch butterfly. Despite its name, when you see how powerfully it attracts pollinators, you will never again think of it as a weed.
Preferring dry, sunny locations, butterfly weed blooms during June to September and is hardy in USDA Zones 4 to 9. Unlike other milkweeds, it has alternating leaves and non-milky sap. While it is slow to emerge in the spring, it reaches two or three inches high and about two inches wide. It is a very low-maintenance plant that tolerates drought and is generally not afflicted by insects or diseases. Additionally, deer usually do not eat butterfly weed.
Although Asclepias tuberosa is a prairie plant, it’s suitable for several types of gardens: meadows, native gardens, nature reserves, rain gardens, and increasingly in formal to semi-formal gardens. For a striking contrast, I enjoy pairing its orange flowers with lavender (Lavendula spp).
Butterfly weed can be grown from seed. A stratification period of two to four weeks is recommended for the seeds prior to planting. I place the seed packets into an airtight container in the vegetable drawer of my refrigerator to prepare them for planting. Since I collect and plant some of my own seeds, I expect to see some flower color variation. For best results, it is recommended that gardeners purchase seeds from reputable vendors.
The butterfly weed produces a large taproot that can extend a foot or more into the soil thus propagation by division is difficult but can be done in the fall, or in early spring prior to new growth. Identifying the ideal plant site is important for butterfly weed. As plants mature, they produce additional stems and tend not to transplant well. The taproot is also referred to as pleurisy root due to its prior medicinal use in treating lung inflammation.
Butterfly weed produces a seed pod after pollination. Measuring about three to six inches long, the seed pods, also known as follicles, turn brown and split, causing the seeds to be disbursed in the wind by their silky-tails. The seed pods can also be pruned to promote additional flowering and to prevent the plants from reseeding. The seed pods are attractive in dried flower arrangements.
One can hardly discuss butterfly weed without also discussing its chief consumer. This noteworthy perennial is significant as a host plant for the monarch caterpillar. Egg-laying female monarch butterflies prefer to lay eggs on the newer growth of the butterfly weed plant and will secrete about 700 eggs during a two to five week period. Depending on temperature, the egg stage lasts three to eight days. Caterpillars, also called larvae, emerge from the eggs and become voracious eaters of the butterfly weed and other milkweeds of the Asclepias genus.
With their yellow, white, and black bands, the monarch caterpillars are easily recognizable. During this nine to 14-day stage, the caterpillars molt as they outgrow their skin. The intervals between molts are called instars.
The monarch caterpillars consume toxins from the butterfly weed (and other milkweeds), called cardiac glycosides. This toxin is more concentrated in the caterpillar than in the leaves of the plant and is carried forward into the next two stages of metamorphism. Along with their bright warning colors and toxicity, predators have learned to avoid them since birds and other animals that eat them become sick and vomit.
Hormones within the caterpillar trigger the next stage of metamorphism and the pupa stage is often referred to as a chrysalis. Caterpillars don’t always remain on the butterfly weed to pupate. They can travel 15 to 20 feet away from the garden to find a location to pupate. After molting for the last time, the caterpillar hangs upside down and silk is produced from a spinneret at the bottom of its head. When encased, this stage lasts eight to 15 days under normal conditions and transformation is completed. Just prior to emerging, the black, orange, and white wing patterns become visible through the chrysalis.
Last year, after redesigning a raised flower bed to include butterfly weed at the side of my house, I noticed my first ever chrysalis.
It was so exciting!
The caterpillar had traveled from the side flower bed to a column on my front porch to pupate, a distance of about 10 feet. By the time I noticed it, the wing patterns were becoming visible and within a few days, the chrysalis was gone. I’ve since learned that they can attach themselves to just about anything to pupate and after emerging as an adult, live for about another two to six weeks. Monarchs that migrate south live all winter, about six to nine months.
Migrating monarchs are particularly vulnerable. Fewer and fewer monarchs survive their southern migration to their wintering sites in central Mexico and California. Widespread use of herbicides that destroy monarch nectar plants such as goldenrod, asters and milkweeds has had a great impact on monarch declines. Pesticide use also contributes to declining numbers of caterpillars and adult butterflies.
If you have well drained soil and are looking to incorporate a native plant into your landscape that is very low-maintenance, drought-tolerant, and meets the needs of the very selective monarch butterfly, I recommend including butterfly weed. By doing so, you can help improve the monarch butterfly population and gain hours of enjoyable pollinator watching at the same time.