Swamp Milkweed (Asclepias incarnata): A Butterfly Garden Essential

Swamp milkweed (Asclepias incarnata) is a standout among milkweeds—well-behaved, clump-forming, and exceptionally attractive to monarchs. With 2015 overwintering numbers at their second-lowest ever, and conservation programs ramping up, this adaptable native should be a staple in every butterfly garden.

Plant Profile

• Botanical name: Asclepias incarnata
• Common names: Swamp milkweed, red milkweed, rose milkweed
• Origin: Native from North Dakota to Texas, east to New England and Georgia
• USDA zones: 3–9 (hardy to –40°F)
• Water: Moist to medium soil
• Light: Full sun to partial sun
• Mature size: 2–4 feet tall, 2–3 feet wide
• Benefits: Very adaptable—tolerates more shade and dry soil than the name suggests
• Seasonal interest: Midsummer blooms, ornamental fall seedpods
• When to plant: Potted or bare-root plants spring through fall

Distinguishing Traits

Noticeable vanilla-spice fragrance. Fairly carefree and widely available at nurseries. Critical: Ask if plants were treated with pesticides—you need clean plants for monarch rearing.

Design Uses

Taller than many wildflowers—place in middle or center of borders. Stays perfectly upright. Beautiful as a specimen or in groups of three with little bluestem (Schizachyrium scoparium), prairie dropseed (Sporobolus heterolepis), or sedges (Carex spp.).

Planting Notes

Wild habitats: marshes, streams, ponds, open prairies, woodland edges in clay to loam. I grow it in partial shade/dry clay and full sun/medium-moist clay.

Plant almost any time. From seed: requires cold moist stratification—sow outdoors late fall through late winter, or stratify in fridge (seeds in damp paper towel in baggie, 1–2 months).

Photo by Joshua Mayer