

Swamp Milkweed Asclepias incarnata
A clump-forming native milkweed of wet meadows and pond edges. Less aggressive than common milkweed, it carries the same monarch-host value with showier rose-pink flowers.
Growing & care
USDA PLANTS · TRY- Sun
- Full sun
- Soil & moisture
- Medium – wet
- Soil pH
- 5–8
- Fertility need
- Medium
- Adapts to
- Medium (loam), Fine (clay)
- Hardiness
- USDA zone 3 – 6
- Height
- 3 – 4 ft
- Spacing
- 2.5–4 ft apart from USDA planting density
- Spread
- Slow
- Growth rate
- Moderate
- Growth form
- Rhizomatous
- Lifespan
- Perennial · moderate
- Foliage
- Broadleaf · coarse texture
- Active growth
- Spring
- Fruit
- Brown persists into winter
- Flower colour
- Pink AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
- Propagate by
- Seed, Sprigs
- Seed starting
- No stratification needed
- Seeds ripen
- Spring – Autumn seed-collection / harvest window
- In the trade
- Routinely available
- Resprouts if cut
- No
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →★ Monarch Larval host plant
A monarch host plant.
Monarch caterpillars eat only milkweeds (Asclepias). As a native milkweed, Swamp Milkweed is a documented larval host across its breeding range.
❧ Caterpillar hosts ~12 caterpillar species
Asclepias supports ~12 caterpillar species.
Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a moderate genus.
Recorded feeding on Asclepias in North America, including:
+ 8 more species → ↑ show fewer
✦ Bees 49 bee visitors
49 native & managed bee species are documented visiting Swamp Milkweed — the 12 most-recorded:
Wildlife & visitors 1 bird · 112 nectaring
Open records of who else uses Swamp Milkweed — a generalist food-web signal, kept separate from the keystone Ecological Value.
Recorded eaten by 1 bird species (fruit, seed, browse):
112 adult butterfly & moth species are recorded nectaring at its flowers — the most-recorded:
How we know this (5) Methods & honest limits
We read each species’ measured specific leaf area (leaf area per unit dry weight) from the Global Spectrum dataset and band it: thin & fast (high SLA), medium, or thick & tough (low SLA). The global median is about 10 mm²/mg.
Honest limits: A species-mean from pooled measurements — individual plants vary with light and site. A broad strategy signal, not a precise per-plant figure.
We place each species on Grime’s competitor–stress-tolerator–ruderal (C–S–R) triangle using the globally-calibrated “StrateFy” method: leaf size drives the competitor score, dense low-area leaves the stress-tolerator score, and thin high-area leaves the ruderal score. The result is a C/S/R percentage mix and one of 19 strategy classes; we show it in plain words and keep the percentages for the curious.
Honest limits: A species-mean strategy from pooled global leaf measurements — a broad ecological signal, not a precise per-plant or per-site value. Derived, never a measured fact.
A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
McKenzie et al. assigned each species a flower colour with a GPT-4V vision model over iNaturalist photos. We use the confident tier plus a separately-labelled lower-confidence top-up (mostly inconspicuous green/brown flowers), and render it as a small tint — never as an asserted fact, and kept out of the written synopsis.
Honest limits: AI image inference (~87% expert agreement on the confident tier); a decorative, confidence-tiered indicator, not a measured trait.
Sources for this entry (37) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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