Shrub · Ericaceae
Swamp azalea
Rhododendron viscosum
Swamp azalea is recorded as native to 22 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 399 counties of those states by USDA PLANTS.
Key facts · USDA PLANTS
Swamp azalea at a glance
- Native in
- 399 counties, across 22 states and territories
- Estimated cold hardiness
- Zone 5b PLANTS minimum temperature −18°F
- Mature height
- 16 ft PLANTS mature height
- Light and water
- Tolerates shade High water use
Estimated cold hardiness: zone 5b. PLANTS gives a minimum temperature of −18°F; zone 5b winters bottom out at −15°F, the coldest half-zone that stays within that limit.
Swamp azalea is recorded as native to 22 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 399 counties of those states by USDA PLANTS.
Counties where it is native
The 15 counties with the most ZIP codes among the 399 where it is listed.
Native counties by state
- Alabama 9 counties
- Arkansas 28 counties
- Connecticut statewide record
- Delaware 2 counties
- Florida 36 counties
- Georgia 55 counties
- Louisiana 20 counties
- Maine 1 county
- Maryland 1 county
- Massachusetts 12 counties
- Mississippi 11 counties
- New Hampshire 2 counties
- New Jersey 21 counties
- New York 20 counties
- North Carolina 48 counties
- Pennsylvania 22 counties
- Rhode Island 4 counties
- South Carolina 23 counties
- Tennessee 5 counties
- Texas 15 counties
- Vermont 1 county
- Virginia 63 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
- Shrub
- Duration
- Perennial
- Mature height
- 16 ft
- Growth rate
- Slow
- Growth form
- Multiple Stem
- Shape
- Erect
- Lifespan
- Moderate
- Active growth period
- Spring
Light and water
- Shade tolerance
- Tolerant (tolerates shade)
- Moisture use
- High water use
- Drought tolerance
- Medium
- Tolerance of waterlogged soil
- Medium
- Precipitation range
- 35 to 55 in per year
Soil
- Soil textures
- Coarse, medium and fine
- pH range
- 4 to 7
- Lime (CaCO₃) tolerance
- Low
- Salinity tolerance
- None
- Fertility requirement
- Low
- Minimum root depth
- 14 in
Climate
- Minimum temperature
- −18°F
- Estimated cold hardiness
- Zone 5b and warmer
- Minimum frost-free days
- 160
- Fire tolerance
- Low
Flowers, leaves and fruit
- Flower color
- Red
- Showy flowers
- Yes
- Bloom period
- Indeterminate
- Foliage color
- Green
- Showy in fall
- No
- Keeps leaves
- No
- Fruit color
- Not recorded
Other
- Toxicity
- None
- Nitrogen fixation
- None
- Nursery availability
- Routinely Available
- Family
- Ericaceae
- PLANTS symbol
- RHVI2
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
- Rhododendron viscosum (PLANTS symbol RHVI2).
- 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