Asclepias sullivantii aka Prairie Milkweed

Asclepias sullivantii is an herb that lives for years. It belongs to the Apocynaceae family. People call it prairie milkweed or smooth milkweed. Another name is Sullivant's milkweed. It comes from central North America. Its range includes the Midwestern United States. It also reaches southeastern Ontario in Canada. Wild plants grow in damp prairies and rich lowlands. They grow in meadows too. Chicago Botanic Garden notes that it prefers prairie sites left undisturbed.

Garden plants grow 2–4 feet (0.61–1.22 metres) tall. Some reach 5 feet (1.52 metres), above the usual range. Thick stems stand upright and hold broad green leaves. The leaves have an oblong, or long oval, shape. They can reach about 0.67 feet (0.20 metres) long. Smooth leaf surfaces help you tell this species apart. So do the pink-red veins down each leaf's center. The leaves curve upward, which adds to its distinct form. The stems and seed pods have no hairs either. Deep taproots make settled plants hard to move without harm.

Pink flowers grow in round groups and have a scent. Missouri Botanical Garden gives June to July as the main bloom season. Chicago Botanic Garden records blooms from May to August. Each flower has a complex shape with hoods and curled horns. These parts make the blooms look like crowns. The flowers draw monarchs and other butterflies to the garden. Later, pods split open and let small brown seeds out. White, silky hairs carry the seeds through the air.

Grow this milkweed in full sun and moist to wet soil. It needs more water than common milkweed. It also copes less well with drought. Sources list it for USDA zones 3–7. Missouri Botanical Garden says it is easy to grow. It needs little care and grows well from seed. Rhizomes, or stems below ground, let it form groups of plants. These groups do not spread in an aggressive way. Plants may sow their own seeds when ripe pods split. Remove pods before they open to limit new seedlings. Leave settled plants in place to keep their roots intact.

Use it in borders, butterfly gardens, and meadows. It also suits areas for native plants. It resists deer, which helps where deer eat plants. Serious pests and diseases are not usual. Aphids may still cause trouble. Aphid control can harm monarch caterpillars and helpful insects too. Keep slugs off young plants as they take root. Plants For A Future lists no known food or medicinal uses. It notes that latex from leaves and stems can yield rubber. Its warning about poison applies to the genus as a whole. It does not cite confirmed reports for this species.