Culture
Easily grown in average, medium to wet soils in full sun. Easily grown from seed, and may self-seed in the landscape if seed pods are not removed prior to splitting open. Once established, it is best to leave plants undisturbed because they develop deep taproots which make transplanting difficult. Spreads by rhizomes to form colonies but is not considered aggressive.
Noteworthy Characteristics
Asclepias sullivantii, commonly called smooth milkweed, Sullivant's milkweed or prairie milkweed, is a herbaceous perennial which is very similar in appearance to common milkweed (Asclepias syriaca) except smooth milkweed has (a.) smooth (glabrous) stems, leaves and seed pods, (b.) leaves with a significant upward sweep and distinctive reddish midveins and (c.) larger flowers. It is found throughout the Midwestern United States and commonly occurs in moist prairies areas including river bottomland and moist meadowlands. It typically grows 2-4' tall (less frequently to 5') on stout, upright stems with broad-oblong, medium green leaves (to 8" long) with pinkish-red midribs. Rounded clusters (umbels to 3" across) of pinkish-white to pinkish-purple, star-like flowers appear mostly in the upper leaf axils over a long bloom period from late spring well into summer. Stems and leaves exude a milky sap when cut or bruised. Flowers give way to smooth seed pods (2-4" long) which split open when ripe releasing their numerous silky-tailed seeds for dispersal by the wind. Seed pods are valued in dried flower arrangements. Flowers are a nectar source for many butterflies and leaves are a food source for monarch butterfly larvae (caterpillars).
The charismatic and imperiled monarch butterfly requires milkweed plants in order to survive. Monarchs migrate into the eastern U.S. from Mexico in spring to lay their eggs on milkweed species plants. Caterpillars hatch from the eggs and consume the milkweed plant foliage as food for growth and development. Mature caterpillars will search for a nearby, sheltered location to enter the pupal stage and form a chrysalis. Inside, they will complete metamorphosis and emerge as an adult butterfly in around 2 weeks. Flower nectar is consumed by adult butterflies as a valuable food source. The 4th or 5th generation of monarch butterflies that emerges in August-September will migrate into Mexico to overwinter as adults. Significant declines in monarch butterfly populations in North America over the course of the 21st century are believed by many experts to be caused by a reduction in milkweed due to widespread use of herbicide-tolerant row crops, climate change, and loss of overwinter sites due to habitat destruction.
To support monarch butterflies, plant species of milkweed that are native to your area.
Genus name honors the Greek god Asklepios the god of medicine.
Specific epithet honors 19th century American botanist William Starling Sullivant.
Problems
No serious insect or disease problems. Aphids can be problematic but attempting to control them can result in inadvertent harm to monarch caterpillars and other beneficial insects.
Uses
Borders, butterfly gardens, prairies, meadows or naturalized/native plant areas.