Asclepias incarnata, which is more commonly known as swamp milkweed, is a native perennial found throughout most of the United States. According to the United States Department of Agriculture’s Natural Resources Conservation Service, this plant occurs naturally in every state except Washington, Oregon, California, Arizona, Hawaii, and Mississippi. The flowers are usually pink or mauve, but white and purple varieties have been cultivated. Swamp milkweed is often grown in flower gardens for its showy and fragrant blooms.
Swamp milkweed prefers damp soil and is often found growing near bodies of water or in low-lying areas such as river bottoms and swamps. Despite the name, swamp milkweed also does well in soil that is well-drained. Garden designers often use it in areas that do not drain particularly well, but this is not required. It does, however, have a deep taproot and does not transplant particularly well once established. This plant prefers full sun.
Like other milkweed plants, swamp milkweed has a milky sap that contains latex, alkaloids, and glycosides. The United States and Germany both attempted to use milkweeds as a source of rubber during World War II, but the latex content is low, and commercialization was never achieved.
Butterflies are drawn to the powerful scent of swamp milkweed for sale online, and Monarch butterfly caterpillars feed exclusively on plants in this family. The alkaloids in the sap give these insects a bitter taste, and birds have learned to associate the bright colors of the caterpillars and the adult butterflies with an unpleasant dining experience. Viceroy butterflies mimic the vivid orange and black coloration of the adult Monarch and benefit from its bitter reputation even though Viceroy caterpillars do not feed on milkweeds and, presumably, taste just fine.
Asclepias incarnate grows in upright clumps of fleshy white tubers. The plants emerge late in the growing season and typically reach a height of three to five feet with multiple branched stems and narrow, lance-shaped opposing leaves. Blooms occur in the early to mid-summer months, and upward-pointing seed pods form when the flowering is done. When these seed pods ripen and split in late summer to mid-fall, they release flat, brown seeds attached to silky silver-white hairs. The hairs act as parachutes and are easily burned by the slightest winds. All milkweed species disperse seeds in this manner.