Common Milkweed, Asclepias syriaca

By Betsy Washington, Northern Neck Native Plant Society

The July Plant of the Month, Common Milkweed, is a lovely, robust, herbaceous perennial festooned with showy clusters of flowers from June to August. A member of the Milkweed genus, Asclepias, it often gets a bad rap for its rhizomatous roots that can spread aggressively; however, this species offers many attractive benefits. For one, it bears showy clusters of flowers in slightly nodding, domed umbels that range from 2 – 3.5” in diameter. Common Milkweed flowers are deliciously fragrant and perhaps best of all, the flowers attract clouds of butterflies, bees, and other pollinators and even hummingbirds. All milkweeds, including Common Milkweed are the sole host for the beautiful and endangered Monarch butterfly, whose numbers have declined precipitously in the last 20 years. A census earlier this year at the Mexico wintering site for North American Monarchs reported the second lowest number of Monarchs ever recorded – 59% less than reported last year! Common Milkweed flowers are followed by distinctive warty light green 2 – 4” long seedpods which split open when ripe to release dozens of seeds tufted with silvery-white silky hairs that assist their wind dispersal. As an added bonus, these pods are a favorite in dried flower arrangements. Finally, Common Milkweed is easy to grow, tolerates poor and dry soils, heat and drought, and is pretty much trouble-free.

Common Milkweed reaches 3 to 5’ in height and can spread into colonies by its rhizomatous roots. It has upright, stout, light green stems and large oblong leaves up to 8” in length arranged opposite each other along the stems. The thick leaves are light green above with reddish mid-veins and covered with short dense hairs below. The flower umbels are held in the upper leaf axils of each stem, with 1 to 3 umbels per stem, creating quite a show. Each umbel is loaded with up to 100 dusty-pink to pinkish-purple individual flowers, each with 5 reflexed petals and 5 raised “hoods” with distinctive curved horns and bloom for 1 – 2 months beginning in June often extending into August. And oh, the fragrance!

A member of the Dogbane family, Apocynaceae, Common Milkweed, like many other family members, has a milky sap that contains cardiac glycosides that are toxic to herbivores such as birds, deer or rabbits. This, of course, is used to advantage by Monarch caterpillars which have co-evolved with milkweeds and have special adaptations that allow them to safely metabolize these toxins and incorporate them into their own tissues and even those of the adults, effectively deterring predators. Similarly, the caterpillars of the Milkweed Tussock Moth also specialize on milkweeds as well as several other insects that are able to safely incorporate the milky sap and gain protection from it. Besides its superb wildlife properties, Native Americans used the leaves and stems of Common Milkweed for fiber and the flossy hairs or “coma” from the seedpods to fill pillows and blankets. In fact, this floss or coma was used as recently as WWII to fill life jackets.

Common Milkweed as its name indicates is common throughout Virginia in fields, pastures, roadsides and other disturbed habitats. It ranges throughout the central and eastern United States and into Canada – following the path of Monarch migration to Mexico.

In the garden, Common Milkweed is a perfect example of Right Plant – Right Place. It can be very aggressive because of its rhizomatous roots and wind-dispersed seeds and is best avoided in small gardens or borders where it may crowd out less robust neighbors. However, these same qualities make Common Milkweed an outstanding plant for naturalizing, meadows, or even along upper shorelines where it can fill any gaps and prevent weeds. The rhizomatous roots also help hold banks and prevent erosion. It also works beautifully in a pollinator garden, especially if confined by hard edges like walkways and walls. Give Common Milkweed well drained soils and full to part sun.

Common Milkweed can be a magnificent plant for the right spot in your landscape where it has room to spread; filling your garden with showy flowers, distinctive seedpods, as well as delightful fragrance – not to mention those clouds of butterflies, bees, and other beneficial insects. And help the Monarchs too!

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Common Milkweed is the Northern Neck Native Plant Society July 2024 Plant of the Month.