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Plant of the Month: Swamp Milkweed

The scientific name of swamp milkweed is Asclepias incarnata. The genus name is derived from Asklepios, the Greek god of medicine and healing, because historically milkweed plants were used in herbal remedies. It's easy to discover the source of the common name: a thick, white sap flows through the stems and leaves.

History and Uses
There are many native milkweed species found throughout the United States. Swamp milkweed is naturally found in wet areas — ditches, moist prairies and meadows, stream banks, forested wetlands, and non-tidal and fresh tidal marshes — but it also grows well in garden settings. Plus, it’s easy to grow from seeds, which germinate readily and reliably. The silky hair on ripe seeds is characteristic of all milkweeds; these “parachutes” allow seeds to travel great distances on the wind.

Milkweeds’ sticky sap contains a toxin that protects plants from being eaten by creatures such as grazing animals. The amount of toxin in the sap varies among species, but most are harmful only if ingested in large quantities. (Explain this to students, and have them wear gloves when handling the plants.) How can toxic plants be considered medicinal? Traditionally, milkweeds were considered a cure for lung and digestive ailments, which indicates their relative safety in small quantities or when processed by an expert.

In the past, Native Americans used leaf fibers to make cord, fishing line, and thread, and bark strips to make lariats. During World War II, milkweed “silks” (from the seed) were used to fill life vests when the traditional filler became scarce. Today, researchers and businesses are developing new uses for milkweed fibers. The best time to harvest milkweed fibers is early winter.

Milkweed for Monarchs
Swamp milkweed has attractive, pale pink to purplish-red flowers that bloom from June through August. Although gardeners enjoy the blossoms, milkweeds are also valued for attracting butterflies, including the Monarch. Other insects also rely on the nectar and pollen of milkweed flowers for food. The leaves are the primary food source of Monarch caterpillars, and the flower nectar a primary food source for Monarch butterflies. What about the toxic chemicals found in the sap? They do not affect Monarch caterpillars or butterflies — in fact, they actually benefit from them! After ingesting leaves, the caterpillars and butterflies store the toxins in their wings and exoskeletons, taking on the same toxic — and therefore, protective — qualities that benefit the plants! Butterfly predators such as birds quickly learn to avoid eating Monarchs because it makes them sick. This also protects butterflies that look like Monarchs, including the Viceroy (a Monarch mimic), because predators can’t easily distinguish between the two.

Milkweeds are widely distributed throughout North America, another characteristic that benefits Monarchs. These butterflies migrate seasonally, flying north in the spring to spend summers in the northern U.S. and Canada, and returning in the fall to overwinter in Texas and Mexico. Milkweeds provide a reliable food source on the journey.

Native milkweed populations are declining due to increasing urbanization and land development. This is a major concern for Monarch enthusiasts. Many are carefully monitoring habitat impacts and tracking their effects on Monarch populations. By planting milkweeds, you can help replace lost habitat for Monarchs and other creatures. For more information visit Monarch Watch.

Growing Swamp Milkweed
This perennial prefers moist to wet soils in full sun. They can grow up to 6 feet tall, but normally reach 3 to 4 feet. Sow seeds, or purchase container-grown specimens to transplant. If you’re thinking of adding swamp milkweed to your schoolyard, place your spring orders with Environmental Concern's native nursery today!


Copyright© 2005 National Gardening Association