Asclepias

When we think about milkweed, we probably picture Asclepias syriaca. Also known as common milkweed, this wildflower is quite noticeable in nature. It usually grows about 1-1.5 m tall and has beautiful large umbels of flowers that are pink or purple. Even if we’ve never seen common milkweed in the wild before, it’s easily identifiable because it’s often featured in photos with monarch butterflies (Danaus plexippus). Common milkweed is an important host plant for the insects.

Recognizing Asclepias syriaca

Native to North America

Common milkweed grows throughout Canada, from Saskatchewan east through New Brunswick and Newfoundland. In the United States, it’s prevalent from the central Great Plains region through to the east coast.

The Lady Bird Johnson Wildflower Center explains that the plant isn’t picky about its habitat. Common milkweed grows in “croplands … pastures, roadsides, ditches and old fields.” In the American midwest, though, the wildflower is mostly found in disturbed sites. A “disturbed site” is an area that’s had its existing vegetation thinned or demolished. This can happen by either natural or man-made occurrences. Forest fires, flooding, insect infestations, and clearcutting are examples of ecological disturbances. Common milkweed prefers disturbed sites because it doesn’t compete well with other plants.

Physical Description

Under the right growing conditions, common milkweed can grow up to 2.5 m tall. In nature, it usually grows to a height of 1-1.5 m. The central stalk is flanked by large oblong leaves. Each stalk can form multiple stems. Up to three flower umbels can form at the top of each stem. (An umbel is a cluster of small flowers on stalks that resemble the ribs of an umbrella.)

Bee Culture describes common milkweed blossoms as having “five petals, a deeply five-parted corolla with lobes that curl backwards, and a crown consisting of five erect or spreading horned hoods.” Each blossom is only about 0.6 cm across. But the umbels can be massive, with up to 100 flowers clustered together. Common milkweed flowers have a strong, sweet fragrance.

Asclepias syriaca blooms in high summer, from June to August.

Growing Asclepias syriaca

Common milkweed has long taproots and it doesn’t transplant well. It’s best started by seed or rhizome cuttings. The United States Department of Agriculture explains that seeds can be sown directly into the soil in the fall. If started indoors, seeds need to be cold stratified for three months. If using cuttings, it’s best to plant those in the fall, so that they have time to develop roots before winter. Make sure each piece has at least one bud and bury them just beneath the soil surface.

Plants prefer dryish, well-drained soil, and full sun. They are cold hardy in Zones 3-9.

Common milkweed won’t bloom until its second year, but it requires little care once it starts growing. It is drought-tolerant and needs watering only in the driest conditions. It does not need fertilizer. However, the United States Department of Agriculture does recommend burning milkweed back in the fall. This will stimulate new growth, with taller, straighter stems, and more vigorous flower and seed production.

Asclepias syriaca as a Source of Food and Nectar

Like all milkweeds, Asclepias syriaca contains cardiac glycoside compounds, which can be toxic. But, as explained by the U.S. Forest Service, some insects have evolved to resist that toxicity. Monarch butterfly larvae, red milkweed beetles, milkweed tussock caterpillars, and the large and the small milkweed bugs all feed common milkweed. As they do so, they store the toxin in their bodies. Because of this, these insects become unpalatable or poisonous to predators. Their coloration–all are orange-red or red and black–signals that they don’t taste good.

Interestingly, common milkweed isn’t as toxic as other milkweeds. As the U.S. Forest Service points out: “What the birds do not know is that northern monarchs feeding on common milkweed accumulate relatively little of the toxic compounds and probably would be edible. The more southern butterflies accumulate large amounts of the compounds from other milkweed species and are in fact toxic.”

While the foliage can be poisonous to organisms that consume it, its abundant nectar is sought out by well over 400 different insects. In an article in the Atlanta Journal-Constitution, Charles Seabrook lists the butterflies that feed on the nectar:

Swallowtails (subfamily Papilioninae)
- According to the Canadian Biodiversity Information Facility, there are 14 species of swallowtails in Canada. These butterflies are large and colourful, with conspicuous tails on their hindwings.
Fritillaries (subfamily Argynninae)
- These butterflies are known for their orange and brown colouring with black markings. Greater fritillaries also have silvery metallic spots on the underside of their wings, which lesser fritillaries do not. There are 35 species in North America, with 26 of those in Canada.
Skippers (family Hesperiidae)
- Skippers are small to medium in size and are have dull grey and brown markings. They are so-named because their flight involves skipping from place to place. There are about 300 species in North America and 72 species in Canada.
Blues (subfamily Polyommatinae)
- Males in this subfamily are typically blue, while females are brown or grey with blue accents. There are 19 species of blues in Canada.
Hairstreaks (subfamily Theclinae)
- Hairstreaks are found on all continents but there are about 90 species in North America and 31 in Canada. They are so-named because many of the species have “one or two hairlike tails on the hindwing and most have wavy or broken lines on the lighter coloured undersurface” of their wings. They also often have a dark spot above their tails on the bottom side of their wings. This is called the “thecla spot” and it resembles an eye when the butterflies sit with their wings folded.

As an important food source for monarch butterflies, and a nectar source for several other species of butterflies, Asclepias syriaca is a terrific addition to most butterfly gardens.

A Note About Invasiveness

Common milkweed produces seed pods that can each contain 50-100 seeds. The seeds are attached to silky tufts that resemble little parachutes. The fluff helps with seed dispersal on the wind. As a result, the plant can spread rapidly. The Canadian Wildlife Federation points out that some jurisdictions (such as Nova Scotia) classify it as a noxious weed. Others, such as Manitoba, list it as a species of concern. It may be grown in controlled home gardens in Manitoba. But if planted in large open spaces, where it could “potentially pose a threat to the economy, environment or human health then the Ministry of Agriculture may be called in to destroy the plants.”

If you’re unsure of how common milkweed is classified in your region, check with your provincial or state ministry of agriculture before planting.

Milkweed is known for attracting monarch butterflies (Danaus plexippus).There are over 200 species of milkweed but Asclepias tuberosa is commonly known as butterflyweed and butterfly milkweed, and rightfully so. The plant is an important host plant for monarch, grey hairstreak, and queen butterflies. It is also an important nectar source for several other butterfly species. While it is native to North America, cultivars have been developed for home gardens. Asclepias tuberosa is a terrific choice for any butterfly garden.

Recognizing Asclepias tuberosa

Native to North America

According to the U.S. Forest Service, butterfly milkweed grows throughout Ontario and Quebec in Canada. In the U. S. A., the plant grows naturally in all but the northwestern states. It is particularly common in the Midwest and Great Plains regions. In the wild, it grows in prairies, open woods, canyons, and hillsides.

Recognizing Asclepia tuberosa

Butterfly milkweed is a beautiful plant that is often grown in home gardens. Compared to other milkweeds that can grow quite tall, Asclepia tuberosa is fairly compact, growing to about 0.5 to 1 m in height.

The plant has a bushy appearance, with numerous stalks forming a clump. Each stalk has narrow oblong leaves and is often topped by several stems. Each stem may host a flower umbel. (An umbel is a cluster of small flowers atop small stems that are similar in shape to the ribs of an umbrella.) The large umbels on butterfly milkweed are often flat or very slightly domed. These provide a handy “landing pad” for butterflies to rest on while extracting nectar.

Butterfly milkweed blossoms are most often bright orange. In fact, one other common name for the plant is “orange milkweed.” However, the Lady Bird Johnson Wildflower Centre states that the flowers might also be red or yellow–and that yellow blossoms predominate west of the 100th meridian. Blossoms are usually 1 cm across, which is relatively large. (The blossoms on species like Asclepias syriaca and Asclepias incarnata are closer to 0.5 cm across.) There are usually about 25 blossoms in each umbel.

Asclepia tuberosa blooms from June through August.

Asclepia tuberosa in the Garden

Butterfly milkweed is easy to grow and care for. Cold hardy in Zones 3-9, it should be planted in full sun. While it prefers well-drained sandy soil, it will grow in any kind of soil, including gravel and clay. It’s drought-tolerant.

The website for the Master Gardener Program at the University of Wisconsin-Madison explains that Asclepia tuberosa has a long taproot and doesn’t transplant well. It’s best started from seeds or cuttings. It’s easiest to sow seeds directly into the soil in the fall, replicating the way the plant self-seeds in nature. If started indoors, seeds need to go through cold stratification for about a month. Cuttings should be started in the fall as well. Take 5 cm sections from the taproot of an established plant and plant the cuttings vertically.

It will take 2-3 years for butterfly milkweed to bloom. But once established, the plant will become thicker each year, and will last for many years.

The one issue that butterfly milkweed may have is aphids–in particular, oleander aphids. The tiny insects rarely harm their host plant and they are tasty food for ladybugs. But if an infestation is bad, aphids can be removed with soapy water or with a high-pressure spray from a hose.

Asclepia tuberosa and Butterflies

According to the Lady Bird Johnson Wildflower Center, Asclepia tuberosa is a host plant for three different species of butterfly larvae:

Monarchs (Danaus plexippus)
- The monarch is one of the best-known species due to its beautiful orange and black coloration and its annual migration. They are found from coast to coast in North America. The Canadian Biodiversity Information Facility reports that monarchs have been spotted at times “well beyond the northern limits of its foodplants.”
Grey hairstreaks (Strymon melinus)
- According to the Butterflies and Moths of North America website, grey hairstreaks are found throughout the United States, with the largest concentrations on the western coast and in the southeastern states. They are rarely found in Canada, except in the southernmost areas near the international border with the United States. Grey hairstreaks are bluish-grey with a tail and large red spots near the tail.
Queens (Danaus gilippus)
- The Butterflies and Moths of North America website describes queen butterflies as chestnut brown, with a black border around their wings and white spots. The underside of their wings has black veining as well. Queens are found from coast to coast in the southern United States. They have been known to stray as far north as South Dakota and New Hampshire.

In addition to being a food source for some butterfly larvae, Asclepia tuberosa also attracts many other butterflies with its rich nectar:

Eastern tiger swallowtails (Papilio glaucus)
Fritillaries (subfamily Argynninae)
Other hairstreaks (subfamily Theclinae)
Painted ladies (Vanessa cardui)
Pipevine swallowtails(Battus philenor)

Butterfly milkweed has gorgeous, bright flowers; it’s easy to care for; and it attracts a wide range of pollinators, including several species of butterflies. Whether you’re planning a butterfly garden or just looking for a plant for your flower bed, butterfly milkweed is a terrific choice.

Asclepias Syriaca

Asclepias Tuberosa