Swamp milkweed (Asclepias incarnata)

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Swamp milkweed

Habit (mature) · ThatLexingtonKyGuy / Wikimedia Commons · CC BY-SA 4.0

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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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Watering and irrigation

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Plant support

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Acid-soil care

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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

°C

°F

Loading current AHS heat-zone and plant heat-fit data at your coordinates…

Where this plant fits

Suitable across 41 ecoregions — 40 climate-resilient through 2070 · 1 suited today. Best matches first.

Appalachian mixed mesophytic forests

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Appalachian-Blue Ridge forests

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Arizona Mountains forests

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Atlantic coastal pine barrens

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Blue Mountains forests

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Canadian Aspen forests and parklands

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Central Pacific Northwest coastal forests

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Central Tallgrass prairie

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Central-Southern Cascades Forests

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Chilean Matorral

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Pollination

Needs cross-pollination

Milkweeds have unusual pollination biology — pollen is packaged in waxy pollinaria (similar to orchids) that visiting insects must catch in leg-claw notches and physically transfer to a separate plant. Bumblebees, wasps, butterflies, and large flies are the primary effective pollinators. While individual flowers can self-pollinate in some cases, fruit set is heavily improved by cross-pollination across multiple Asclepias incarnata individuals. Plant in groups of 3+ for reliable seed production.

Compatible pollinizers

Multiple Asclepias incarnata plants (or any compatible Asclepias species) within ~30 feet improve fruit set meaningfully. The pollinaria pollination mechanism requires physically distinct visiting insects to carry pollen from one plant to another.

Within

30 feet of a partner

Bloom timing

Partner bloom-time matching: recommended

Plants don't grow alone

Larval host

Specialist

Butterfly

Monarch butterfly (Danaus plexippus)

Asclepias incarnata is among the canonical monarch larval host plants — same status as A. syriaca but in a wet-meadow rather than disturbed-roadside ecological context. Caterpillars sequester the cardiac glycosides from the milkweed sap as predator-deterrent defense. Planting swamp milkweed is the wet-site equivalent of the common-milkweed conservation action.

Larval host

Specialist

Moth

Milkweed tussock moth (Euchaetes egle)

Milkweed tussock moth (Euchaetes egle) larvae are Asclepias specialists alongside monarchs — both species sequester cardiac glycosides from milkweed sap for chemical defense.

Pollinates

Bee

Common eastern bumblebee (Bombus impatiens)

Nectar forage

Butterfly

Eastern tiger swallowtail (Papilio glaucus)

For people

Toxic — do not consume

NC State Extension tags swamp milkweed as Poisonous — "Low severity poison characteristics." All plant parts contain cardiac glycosides and resinoids; ingestion causes gastrointestinal upset in humans, cats, dogs, and horses. The same cardiac glycosides are what make monarch caterpillars (which sequester the compounds from milkweed sap) unpalatable to vertebrate predators — the wedge-relevant ecology. Contact dermatitis from sap can occur in sensitive individuals.