Common milkweed (Asclepias syriaca) has qualities which, in the plant kingdom, are considered quite uncommon. This most prolific and notorious of all our native Ontario milkweeds was on Ontario’s Noxious Weed List prior to 2014, in part, because of its rampant potential to significantly reduce crop yields on agricultural lands. It also can be harmful to grazing livestock due to the toxicity of the cardiac glycosides found in all parts of the plant. Nowadays, despite these concerns, common milkweed and its relatives in the Asclepias genus enjoy growing recognition for their considerable contributions to humans and the natural world.
Let us count the ways….
Contribution to local food webs
First, milkweeds are important contributors to local food webs. Their flowers, leaves, stems and roots support dozens of insects like the larvae of the milkweed tussock moth, large and small milkweed bugs, and the red milkweed beetle. Milkweed aphids attract beneficial predators like lacewings, parasitic wasps, and ladybugs, and benefactors like ants which farm them for their honeydew. Milkweed flowers are nectar magnets for pollinators, including bees, wasps, butterflies, moths and beetles. They are one of those keystone plants in the biodiverse garden.
Below left, large and small milkweed bugs feeding on seeds, and right, a great golden digger wasp on swamp milkweed.
Milkweeds are a host plant
Secondly, milkweeds are the sole host plant for the larvae of our eastern migratory monarch butterfly whose population has declined by ∼84% between 1993 and 2024. Additional common milkweed would help Canada meet its share of the trinational eastern migratory monarch butterfly recovery target While all of our native milkweed species can serve as Monarch host plants, in a 2018 Iowa State University study on monarchs’ preferences, the results showed that monarchs preferred to lay eggs on common milkweed (Asclepias syriaca) and swamp milkweed (Asclepias incarnata). The researchers found that other milkweed species may be less effective as hosts for monarchs for reasons such as plant structure and species abundance.
Below, the caterpillar of the monarch butterfly on milkweed
Milkweed as medicine
Thirdly, it is not surprising that Asclepias was originally named for the Greek god of healing because of its rich indigenous medicinal history. Milkweed has and is still being used as a natural remedy for a variety of ailments, including treating skin, respiratory, lung and digestive disorders. The cardiac glycosides in milkweeds have been shown to increase the force of heart contraction and have been used to treat heart conditions. “Cardiac glycosides also have potential anti-cancer application; in the lab, they exhibit properties toxic to cancer cells.” Milkweeds | Native Medicinal Plant Research Program Cardiac glycosides are only one of several compounds under research for pharmaceutic and therapeutic applications.
Culinary uses
Fourth, despite their toxicity, milkweeds have historically been, and are being appreciated as, an important source of food and fiber. Cooked properly to reduce toxins, their young shoots, flowers, and pods, can be enjoyed in a variety of ways. One forager, for example, recommends boiling the shoots for 15-20 minutes before adding to a frittata. (Northeast Foraging, Leda Meredith, Timber Press, 2014).
Note that it is important to properly identify the young plant before harvesting because of similarities to native poisonous dogbane.
Below, left, popular picked milkweed pods, and right, a cordial made from the flowers.
Like our native dogbanes, milkweed stems, especially those of swamp milkweed (Asclepias incarnata), contain fibrous material that can be made into cordage. Bird species like orioles, aware of the strong fibers in the stems, are often observed stripping them from the plants to use in their elaborate nests.
Bird-friendly gardens may include swamp milkweed for this reason, and their gardeners during fall/spring clean-up, will leave in place previous year’s stems for nesting material.
Innovative uses for milkweed pod floss
Fifth, milkweed pod floss, especially that of common and swamp milkweed, is incredibly useful. During World War II, Americans used the floss to make life jackets for the military. According to the US Department of Agriculture, the floss is “six times more buoyant that cork and five times warmer than wool”.
Currently, other applications of milkweed floss are being studied. The American bedding company, Ogallala, has created a new product, Hypodown®, a “revolutionary blend of goose down and milkweed fiber” now sold in its line of luxury bedding. According to the company, the use of milkweed floss offers multiple benefits. “Milkweed fiber is hypoallergenic and has properties that help trap and suppress allergens commonly found in down, reducing the likelihood of allergic reactions. Additionally, it enhances breathability, durability, and moisture-wicking capabilities compared to traditional down or synthetic materials. Its moisture-wicking ability is notably higher, making it adept at regulating body temperature by pulling moisture away from the body faster than down alone or synthetic materials.”
No wonder the Audubon Society recommends milkweed floss as a bird-nesting material to leave in your garden! For more information on nesting materials: What Nesting Materials Are Safe for Birds? | Audubon Leaving the pods over winter and early spring can support a variety of wildlife, as seen in the photo below.
The ‘fluff’ in this photo is milkweed floss, carried up to a vacated bird nest by an industrious mouse. Buoyant, soft and water resistant, milkweed floss is a material with many desirable characteristics. Milkweed Floss | Good Natured
Beautiful flowers
Finally, there’s the stunning inflorescence every garden could showcase, a flat-topped or spherical umbel, exquisitely vanilla-scented, like the three below.
These flowers are incredibly complex. From the top (picture below left), you can see the crown of the flower which sits above its 5 petals (usually recurved) and 5 sepals. It has 5 nectar-containing hoods, and 5 horns, and in the centre, the fused male and female reproductive organs (the gynostegium) containing pollen sacs (pollinia) and side slits where the pollen sacs must be placed for successful pollination. Unlike most flowers, milkweed does not have pollen grains, but pollinia (pollen sacs), which hook onto pollinators collecting nectar, like with the bee (below right).
A word about tropical milkweed
Tropical milkweed (Asclepias curvassica), above, is a tender perennial native to Mexico, Central and South America, and the Caribbean. Easy to grow, it is often planted as an annual here. Because it is not hardy in Ontario, most of the concerns over growing it in more southernly areas don’t apply to us (yet). Regardless, when choosing milkweeds for your garden, it is recommended to grow native species, not tropical milkweed. For more information:
Tropical Milkweed—a No-Grow | Xerces Society
Milkweed muddle: why NOT to plant tropical milkweed | Wild Pollinator Partners
Eleven Ontario native milkweeds
Butterfly milkweed (Asclepias tuberosa), bottom left, is a drought-tolerant, clump-forming, shorter (75 cm) milkweed perfect for sunny spots in the urban garden. Though native to Ontario, butterfly milkweed is uncommon in the wild. Its sap is clear, not milky white like that of other species.
Swamp milkweed (A. incarnata), below right, is another clump-forming, well-behaved milkweed for the urban garden. It prefers full sun to part shade in moister soils, but will tolerate drier ones with periodic watering. Common across the province, it’s much taller (1.5m), and beautifully scented. ‘Ice Ballet’ is a lovely white variety.
Whorled milkweed (A. verticillata), below left, is a shorter milkweed (30-60 cm) which prefers dry to average soil, and full sun to part shade. It is a more delicate plant, with whorled, narrow leaves, but is a suckering, aggressive spreader. Although widely distributed in the United States, it is very rare in the wild in Ontario.
Common milkweed (A. syriaca), below right, is the most abundant milkweed in the province. It grows in average, poor soils in full sun. It’s a taller plant (2.5m), and an aggressive, rhizomatous spreader. Plant where it will have plenty of space.
Purple milkweed (A. purpurescens), below left, is a less aggressive, clump-forming, showy, species with deep rose-pink blooms. It grows in dry to moist well-drained soils in full to part sun. It is rare in the wild in extreme south western Ontario.
Poke milkweed (A. exaltata), below centre, is the best milkweed for a shady location. It is tall (1.5m), and grows in average, well-drained soil. Uncommon in the wild in Southern Ontario, it can be found in open woods and at the edges of forests.
Oval-leaf Milkweed (A. ovalifolia), below right, is a short (30-60 cm), rare plant found in the north west of the province It prefers sun to part shade, and dry soil.
Prairie milkweed (A. hirtella)), below left, grows in dry to moist soil in sun to part shade. A tall milkweed (90-120 cm), it has greenish flowers and narrow leaves. ”The Ojibway Prairie is the only habitat in all of Canada where Asclepias hirtella, the tall green milkweed, can be found.” Keeping milkweed in the prairie – Wildlife Preservation Canada
Green Comet milkweed (A. viridiflora), below right, is another shorter milkweed (30-60 cm) that prefers open sandy woods and dry hillsides. It grows in full sun to part shade. It is rare in the wild in southern Ontario.
Four-leaved milkweed (A. quadrifolia), below left, is endangered in Ontario, with two small populations found only in Prince Edward County. It is short (50 cm), and prefers dry soil in sun to shade. Look for it in dry woodlands and woodland alvars. Four-leaved milkweed | ontario.ca
Sullivant’s milkweed (A. sullivantii), below right, is similar in appearance to common milkweed. It grows in moist to average soil in full sun to part shade. It is rare in the wild, growing in prairies in extreme southern Ontario.
Enjoyable reading on milkweeds
The Milkweed Lands: An Epic Story of One Plant: Its Nature and Ecology, September 26, 2023 by Eric Lee-Mäder (Author), Beverly Duncan (Illustrator), Joan Edwards (Foreword)
