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Swamp milkweed
Habit (mature) · ThatLexingtonKyGuy / Wikimedia Commons · CC BY-SA 4.0
Limited coverage
Swamp milkweed
Asclepias incarnata
A more refined garden-behaved cousin of common milkweed (Asclepias syriaca) — same monarch host status and ecological value, but clumping rather than aggressively spreading, well-suited to rain gardens and consistently moist sites. Pink fragrant flower clusters from mid-summer through early fall; 2005 NC Wildflower of the Year. NC State tags Poisonous (cardiac glycosides) — the same toxicity that makes monarch caterpillars unpalatable to vertebrate predators.
Native: 44 US states + 6 CA provinces
Review: Source-backed
Climate fit: broad (90/100)
Pollinator
Border
Focal point
Light
Full sun / Part shade
Water
Consistent moisture
Mature size
36-60" tall · 24" apart
Hardy in zones
3a-9b
brutally cold to frosty winters
Summer heat range
Cool-Hot
cool to hot summers Interim Plotwright tier until the plant AHS range is authored.
Native in Illinois
Yes
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Winter protection and storage
Frost cloth, plant covers, bulb/tuber storage supplies, burlap, and cold frames.
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Watering and irrigation
Watering cans, soaker hoses, drip kits, moisture meters, and timers.
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Plant support
Stakes, cages, trellises, ties, clips, arbors, and heavy-duty supports.
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Acid-soil care
Sulfur, acid-loving plant fertilizer, pine bark, and pH monitoring.
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Soil testing and pH
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A documented larval host for the Milkweed tussock moth and 1 other species — specialist wildlife that depend on plants like this to reproduce.
Wildlife relationships
Cold hardiness
Now
Zone 6b
USDA
Chicago, IL · 1991-2020 average annual coldest day
Source: USDA Plant Hardiness Zone Map 2023 (1991-2020 climatology) via ArcGIS FeatureServer
Well-suited
2050
Zone 7b
Plotwright
Your zone + climate-model shift · SSP3-7.0 (regional rivalry)
Well-suited
In plain terms: cold winters — coldest nights typically around -3°F.
Well-suited today and still thriving in 2050.
Heat tolerance
Loading current AHS heat-zone and plant heat-fit data at your coordinates…
Sources & citations
Cite this page
For lesson plans, articles, or research that uses this page. To cite a single upstream fact instead, use its specific source listed below.
Plotwright. (2026, May 17). Swamp milkweed (Asclepias incarnata). Retrieved 2026, June 5, from https://plotwright.garden/plants/swamp-milkweed
Sources for every fact
Every fact on this page traces to a source. 18 fields cited18 source-backed.
NC State Extension Gardener Plant Toolbox
University extension service
Backs 17 fields
Identity
Summary
Plant type
Light
Moisture
Hardiness
Heat zone
Size
Spacing
Habit
Design roles
Seasonal interest
Growth stages
Lifecycle
Regional guidance
Success tips
Designer notes
Wikimedia Commons
Photo · CC BY-SA 4.0
Backs 1 field
Image
Community photos
The photos above are our reviewed reference set, curated for accuracy.
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