Asclepias incarnata
An elegant, clump-forming milkweed with showy clusters of rose-pink flowers, native to wet meadows, streambanks, and marsh edges. A major Monarch butterfly host plant and one of the most ornamental milkweeds for garden cultivation.
Bloom & Fruit
Showy, upright umbels of rose-pink to mauve flowers, each umbel bearing 20-40 individual florets. Flowers are smaller and more delicate than Common Milkweed but produced in greater abundance. Blooms from mid-summer into early fall.
Growing Conditions
Garden Uses
- Larval HostHost plant for butterfly and moth caterpillars. Essential for supporting complete insect life cycles.
- Pollinator HostAttracts bees, butterflies, and beneficial insects. Plant near vegetable gardens to boost pollination.
Companion Planting
These species thrive in similar conditions and complement each other ecologically.
Where to Buy
Ecology
Native Habitats
Associated Fauna
Propagation
- Seed (cold-moist stratification 30 days)
- Division (spring)
Details
Description
Asclepias incarnata is a clump-forming, non-rhizomatous perennial milkweed with an upright, elegant habit. Plants reach 90-150 cm in height with multiple slender, branching stems. The leaves are narrow, lance-shaped, and opposite, 7-15 cm long, with a smooth texture unlike the fuzzy leaves of Common Milkweed. Despite the common name, Swamp Milkweed does not have milky sap as copious as other Asclepias species.
The flowers are among the most attractive of any milkweed: upright, domed umbels of deep rose-pink to mauve, each umbel 5-8 cm across with 20-40 individual florets. Blooming begins in July and can continue through September, making it one of the latest-flowering milkweeds in Ontario. Seed pods are slender, smooth, and held upright on the stems — quite different from the warty, pendulous pods of Common Milkweed.
Growing Conditions
As its common name suggests, Swamp Milkweed thrives in moist to wet soils. It naturally occurs along streambanks, marsh edges, wet meadows, and ditches. Requires full sun and consistently moist, rich soil. Unlike Common Milkweed, it does not spread aggressively by rhizomes and forms well-behaved, gradually expanding clumps. Ideal for rain gardens, pond edges, and moist perennial borders.
Hardy from Zone 3 through Zone 9. In Ontario, it is widespread in suitable wetland and moist meadow habitats. Tolerates heavy clay soils better than most milkweeds. Not drought-tolerant — plants in dry soil will be stunted and may not flower.
Phenology
Emerges in mid to late spring. Flowering spans July through September, with peak bloom in August — later than Common Milkweed, providing a critical late-season nectar source. Seed pods develop through late summer and split open in September-October. Foliage turns yellow in fall. The plant dies back to a woody crown each winter; unlike Common Milkweed, there are no persistent rhizomes.
Ecology
A major Monarch butterfly host — the smooth, tender leaves are readily consumed by Monarch caterpillars, and the plant's late flowering season extends nectar availability for migrating adult Monarchs. The showy pink flowers are highly attractive to a wide range of pollinators including bumble bees, honey bees, native solitary bees, butterflies, and hummingbirds.
Like all milkweeds, the plant contains cardiac glycosides that make it toxic to vertebrate herbivores. Deer and rabbits avoid it. The latex sap, while less copious than in Common Milkweed, still deters most insect feeding except by specialist milkweed herbivores adapted to the toxins.
Propagation
Seeds require 30 days of cold-moist stratification. Sow in fall or stratify for spring planting. Seedlings are slower to establish than Common Milkweed but grow rapidly once their root system develops. Flowering typically begins in the second year. Clumps can be divided in early spring, though the woody crown makes division more challenging than rhizomatous species. Unlike Common Milkweed, Swamp Milkweed is not aggressive and can be safely planted in mixed borders.