Wildflower (forb) · Asclepiadaceae
Swamp milkweed
Asclepias incarnata · includes its varieties and subspecies
Swamp milkweed is recorded as native to 42 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 1,356 counties of those states by USDA PLANTS.
Key facts · USDA PLANTS
Swamp milkweed at a glance
- Native in
- 1,356 counties, across 42 states and territories
- Estimated cold hardiness
- Zone 3b PLANTS minimum temperature −38°F
- Mature height
- 4.9 ft PLANTS mature height
- Light and water
- Full sun (shade-intolerant) High water use
Estimated cold hardiness: zone 3b. PLANTS gives a minimum temperature of −38°F; zone 3b winters bottom out at −35°F, the coldest half-zone that stays within that limit.
Swamp milkweed is recorded as native to 42 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 1,356 counties of those states by USDA PLANTS.
Counties where it is native
The 15 counties with the most ZIP codes among the 1,356 where it is listed.
Native counties by state
- Alabama 2 counties
- Arkansas 5 counties
- Colorado 11 counties
- Connecticut statewide record
- Delaware 3 counties
- District of Columbia 1 county
- Florida 21 counties
- Georgia 8 counties
- Idaho 7 counties
- Illinois 99 counties
- Indiana 77 counties
- Iowa 28 counties
- Kansas 66 counties
- Kentucky 68 counties
- Louisiana 5 counties
- Maine 14 counties
- Massachusetts 14 counties
- Michigan 76 counties
- Minnesota 76 counties
- Missouri 84 counties
- Nebraska 54 counties
- Nevada 1 county
- New Hampshire 10 counties
- New Jersey 21 counties
- New Mexico 4 counties
- New York 46 counties
- North Carolina 60 counties
- North Dakota 14 counties
- Ohio 86 counties
- Oklahoma 12 counties
- Pennsylvania 62 counties
- Rhode Island 5 counties
- South Carolina 7 counties
- South Dakota 27 counties
- Tennessee 38 counties
- Texas 16 counties
- Utah 7 counties
- Vermont 13 counties
- Virginia 95 counties
- West Virginia 39 counties
- Wisconsin 71 counties
- Wyoming 3 counties
Growing traits
Values from the PLANTS characteristics record. “Not recorded” means PLANTS has no value; nothing here is estimated except the zone.
Growth
- Growth habit
- Forb/herb
- Duration
- Perennial
- Mature height
- 4.9 ft
- Growth rate
- Moderate
- Growth form
- Rhizomatous
- Shape
- Erect
- Lifespan
- Moderate
- Active growth period
- Spring
Light and water
- Shade tolerance
- Intolerant (full sun (shade-intolerant))
- Moisture use
- High water use
- Drought tolerance
- None
- Tolerance of waterlogged soil
- High
- Precipitation range
- 15 to 65 in per year
Soil
- Soil textures
- Medium and fine
- pH range
- 5 to 8
- Lime (CaCO₃) tolerance
- Medium
- Salinity tolerance
- None
- Fertility requirement
- Medium
- Minimum root depth
- 18 in
Climate
- Minimum temperature
- −38°F
- Estimated cold hardiness
- Zone 3b and warmer
- Minimum frost-free days
- 107
- Fire tolerance
- Low
Flowers, leaves and fruit
- Flower color
- Red
- Showy flowers
- Yes
- Bloom period
- Fall
- Foliage color
- Green
- Showy in fall
- No
- Keeps leaves
- No
- Fruit color
- Brown
Other
- Toxicity
- Moderate
- Nitrogen fixation
- None
- Nursery availability
- Routinely Available
- Family
- Asclepiadaceae
- PLANTS symbol
- ASIN
Source & data date
- Source
- USDA NRCS PLANTS Database: county distribution records, native status and plant characteristics. CC0 (public domain dedication, per the data.gov catalog record).
- Kew’s World Checklist of Vascular Plants (WCVP): native or introduced status by state. CC BY 3.0.
- USGS US-RIIS (ver. 2.0): species listed as introduced are excluded. CC0.
- Citation
- USDA, NRCS. 2026. The PLANTS Database (https://plants.usda.gov, 11/04/2026). National Plant Data Team, Greensboro, NC USA.
- Govaerts R. (ed.) (2026). WCVP: World Checklist of Vascular Plants. Facilitated by the Royal Botanic Gardens, Kew. Data file dated 2026-06-04, http://sftp.kew.org/pub/data-repositories/WCVP/ (retrieved 2026-11-04). Paper: Govaerts R. et al. (2021) The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. Scientific Data 8, 215.
- Data date
- Retrieved from PLANTS on November 4, 2026; WCVP data file dated June 4, 2026.
- Scope
- Asclepias incarnata (PLANTS symbol ASIN), including 2 varieties and subspecies folded into the species.
- Method
- A species is listed when it is recorded as native to the state in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in the county by USDA PLANTS. Species PLANTS labels both native and introduced are listed separately. Full method · All sources