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.
Smooth milkweed (also commonly known as Sullivant's milkweed and prairie milkweed) is a rough, weedy perennial which is very similar 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 a Missouri native plant which commonly occurs in moist prairies areas including river bottomland and moist meadowland mostly north of the Missouri River. 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). Species is named after 19th century American botanist William Starling Sullivant.
No serious insect or disease problems. Somewhat weedy in appearance and can spread somewhat aggressively in optimum growing conditions.
Borders, butterfly gardens, prairies, meadows or naturalized/native plant areas.