Flower profile
Swamp azalea
Rhododendron viscosum
Swamp azalea (Rhododendron viscosum) is a shrub in the Ericaceae family, native in the lower 48 states, blooming mostly June–July across the U.S.
Swamp azalea is a flowering plant that USDA PLANTS lists as native in the lower 48 states.
*iNaturalist research-grade observations, as of October 17, 2026.
On our lists for: Rhode Island
Quick look
Rhododendron viscosum, the swamp azalea, clammy azalea or swamp honeysuckle, is a species of flowering plant in the heath family Ericaceae. A deciduous shrub, it grows to 2.5 m (8.2 ft) tall and broad. It is native to the eastern United States. It has rounded matt green leaves. In early summer it produces funnel-shaped white flowers flushed pink. The flowers have prominent stamens and are strongly fragrant.
- It belongs to the Ericaceae family. iNaturalist
- USDA PLANTS describes it as a shrub with a perennial life cycle. USDA PLANTS
- USDA PLANTS lists it as native in the lower 48 states and records it in 24 states. USDA PLANTS
- NatureServe lists it as native to Rhode Island. NatureServe
- USDA PLANTS lists its flower color as red. USDA PLANTS
- USDA PLANTS gives its bloom period as indeterminate. USDA PLANTS
- USDA PLANTS lists a mature height of about 16 ft. USDA PLANTS
- iNaturalist has 157 research-grade sightings of it in Rhode Island, ranking #101 among the 164 flowers on our Rhode Island list. iNaturalist
When does it bloom?
Conservation status
- Federal (U.S. ESA)
- Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. USFWS ECOS
- NatureServe global
- G5 Secure worldwide. NatureServe
- Rhode Island
- Not listed Not on Rhode Island Rare Plants 2016 (RI Natural History Survey, from the RI Wildlife Action Plan; informational, Rhode Island has no state plant-protection listing law). NatureServe: SNR, not yet ranked in Rhode Island. RI rare plants 2016
- Rare elsewhere
- Other states where NatureServe ranks it rare or missing: ME (S1), OK (S1), WV (S1). (S1 critically imperiled, S2 imperiled, SH possibly extirpated, SX presumed extirpated.)
Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.
Can you eat it?
NC State Extension lists it as poisonous to humans (severity: low). Poisonous parts: bark, flowers, fruits, leaves, roots, seeds, stems. Symptoms they list: “While the plants are known to contain toxins, ingestion of moderate amounts of azalea (nectar or leaves) poses little toxic hazard.” NC State Extension
ASPCA's entry “Azalea” (Rhododendron spp), which covers the whole genus, lists it as toxic to dogs, cats and horses. Signs include: Vomiting (not in horses), diarrhea, weakness, cardiac… ASPCA
🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.
Where does it grow?
USDA PLANTS records swamp azalea in 24 states plus Washington, D.C.
recorded by USDA PLANTS on our state lists not recorded
See the full list of states
Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Louisiana, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West Virginia; District of Columbia.
Rhode Island counties with USDA records: Kent, Newport, Providence, Washington.
Growing conditions
USDA PLANTS gives Swamp azalea a low shade tolerance, medium drought tolerance and high moisture use. It is rated for soil pH 4.0 to 7.0 and winter lows down to -18 °F.
- Shade tolerance
- Low
- Drought tolerance
- Medium
- Moisture use
- High
- Soil textures it is adapted to
- coarse, medium, fine
- Soil pH range
- 4.0 to 7.0
- Minimum temperature tolerated
- -18 °F
- Frost-free days needed (minimum)
- 160
- Annual precipitation range
- 35 to 55 inches
- Minimum root depth
- 14 inches
- Salinity tolerance
- None
- Fertility requirement
- Low
- Growth rate
- Slow
- Lifespan
- Moderate
- Active growth period
- Spring
- Fruit or seed
- · Summer to Fall
- Can be propagated by
- bare root, container, seed
- Commercial availability
- Routinely Available
From the USDA PLANTS characteristics data for RHVI2. USDA ratings are general guidance for the species, not a guarantee for your garden.
Names, range and relatives
Other scientific names (synonyms in USDA PLANTS): Azalea serrulata, Azalea viscosa, Rhododendron coryi, Rhododendron serrulatum.
County records: USDA PLANTS lists it in 404 counties across 23 states; the most are in Virginia (63), Georgia (55), North Carolina (48).
Other Rhododendron on Bloomipedia (11): Rhododendrons and azaleas, Great rhododendron, Labrador tea, Pinxter flower, Pacific rhododendron, Flame azalea, Mock azalea, Rhodora, Mountain azalea, Catawba rhododendron.
More from the Ericaceae family (55 on Bloomipedia; most observed first): Ghost pipe, Striped wintergreen, Mountain laurel, Eastern teaberry (wintergreen), Salal, Woodland pinedrops, Pinesap, Trailing arbutus (mayflower).
More Rhode Island flowers
Sources
- USDA, NRCS. PLANTS Database, profile RHVI2.
- iNaturalist, Rhododendron viscosum: taxonomy, research-grade observation counts and “Flowering” annotations, retrieved October 17, 2026.
- Wikipedia, Rhododendron viscosum (lead quoted under CC BY-SA 4.0).
- Rhode Island: Rhode Island Rare Plants 2016 (RI Natural History Survey, from the RI Wildlife Action Plan; informational, Rhode Island has no state plant-protection listing law).
- USFWS, ECOS species database (ESA listing check), October 17, 2026.
- NatureServe Explorer, Rhododendron viscosum (global and state ranks).
- Edibility and toxicity: NC State Extension; ASPCA.
- Photo: Tyler Ekholm via iNaturalist · CC BY 4.0 · resized.