# Swamp Azalea (Rhododendron viscosum)

> Sticky, clove-scented white flowers from May to July, one of the last wild azaleas to bloom, on a shrub that takes wet, acid ground.

Also called clammy azalea, swamp honeysuckle, white swamp azalea, hammock-sweet azalea, Azalea viscosa, Rhododendron serrulatum. Category: Native Shrubs. Grown from seed by Blue Whale Trees. Web version: https://bluewhaletrees.com/plants/swamp-azalea/

![Swamp azalea (Rhododendron viscosum) white tubular flowers among glossy green leaves](https://bluewhaletrees.com/img/plants/swamp-azalea-h1610-800.jpg)
*Photo: HorsePunchKid, CC BY-SA 4.0 · [Wikimedia Commons](https://commons.wikimedia.org/wiki/File%3ASwamp_Azalea_Blooming.jpg)*

## Facts

- Type: Shrub
- Mature height: 3 to 8 ft
- USDA hardiness zones: 4 to 9
- Grows wild in: Stream banks, the coast, the forest understory, swamps and wet flats
- Native range: 24 states and the District of Columbia, north to Maine, south to Florida and west to Texas (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 and the District of Columbia)
- Sun: Part, Full
- Soil moisture: Wet, Average
- Growth rate: Slow
- Traits: Showy flowers, Tolerates wet soil, Wildlife value, Fall color
- Sold as: Saplings, Seed

Heights and zones are typical ranges for the species in cultivation; local conditions and seed source shift them.

## Availability

Not yet priced online. Ask at captain@bluewhaletrees.com or leave an email on the web page to be told when it is listed.

## Notes

Swamp azalea is the late white azalea of eastern wetlands. Its name viscosum means sticky, for the glandular hairs on the flower tube, which also gave it the name clammy azalea. The scent, musky and clove-like, is strongest at night. It reached British gardens in 1734 and is a reputed parent of many garden azaleas. Maine lists it as endangered, at the northern limit of its range. Plant it in damp ground near a pond or stream, where it often thrives.

## Size, growth and what to expect

No source rates swamp azalea's growth, so our growth estimator treats it as slow, like our other wild azaleas, about a foot a year. It usually grows 3 to 5 feet tall, less often 8, and 3 to 8 feet wide. In the wild it can reach 15 feet or more.

Clusters of 4 to 9 white or pale pink flowers open from May to July, after the leaves, one of the last native azaleas to flower. Each is about an inch and a quarter across, a narrow tube that flares into five lobes. The capsules follow from July to October. The leaves turn yellow, orange and purple in fall.

It grows wild from Maine and New Hampshire south to central Florida and west to Tennessee, Arkansas, Oklahoma and Texas. Its home is acid swamps, bogs, seepage slopes, pocosins, wet pine flatwoods and shrub balds, up to about 4,900 feet.

## How to grow Swamp Azalea

Swamp azalea does best in part shade and takes some sun, but afternoon sun can scorch the leaves. It wants acid, humus-rich soil that stays moist or wet, and it stands periodic flooding, though its roots must not sit under water. Keep it clear of black walnut and butternut, whose roots release juglone, which can kill azaleas. Set plants 5 feet apart and keep them 4 feet from a wall. At its size it can go within 15 feet of overhead wires.

Saplings ship potted. Plant dormant plants in early spring or fall, in a hole three times as wide as the root ball and no deeper, and put the native soil back in. Mulch with wood chips, bark or pine needles, kept off the stems. The seed is dust-fine and needs light, with no chilling. Sow it in winter on the surface of damp milled sphagnum, uncovered, at room temperature under lights and a clear cover. Seedlings come up in one to three weeks.

Water weekly through the first two summers unless the ground stays damp, and never let the shallow roots dry out. Never hoe or dig over them. Rabbits seldom harm it, and where deer are common, cage young plants as for our other wild azaleas. Prune, if at all, right after bloom.

Each flower carries both male and female parts, and bees, moths and hummingbirds come to the flowers. Swamp azalea sets seed with its own pollen, so one plant bears alone, though bumblebees must carry the sticky pollen between flowers. It crosses at times with sweet azalea, and seed from a plant near other azaleas in bloom may give hybrids. Root rot troubles it less than most azaleas, though lace bugs, aphids and mites can mark the leaves. Every part of the plant is poisonous if eaten, and honey from its flowers can be too.

## Sources

- [NC State Extension Gardener Plant Toolbox: Rhododendron viscosum](https://plants.ces.ncsu.edu/plants/rhododendron-viscosum/)
- [Missouri Botanical Garden Plant Finder: Rhododendron viscosum](https://plantfinder.mobot.org/PlantFinderDetails.aspx?taxonid=280018)
- [Lady Bird Johnson Wildflower Center: Rhododendron viscosum](https://www.wildflower.org/plants/result.php?id_plant=RHVI2)
- [Flora of North America, vol. 8: Rhododendron viscosum](http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250065656)
- [Trees and Shrubs Online: Rhododendron viscosum](https://www.treesandshrubsonline.org/articles/rhododendron/rhododendron-viscosum/)
- [USDA Forest Service, Woody Plant Seed Manual (2008), Rhododendron chapter](https://www.fs.usda.gov/nsl/Wpsm/Rhododendron.pdf)
- [NatureServe Explorer: Rhododendron viscosum](https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.129022/Rhododendron_viscosum)
- [Maine Natural Areas Program: Maine Rare Plant List, 2021 tracking list](https://www.maine.gov/dacf/mnap/features/rare_plants/plantlist.htm)
- [Maine Natural Areas Program: Clammy Azalea fact sheet](https://www.maine.gov/dacf/mnap/features/rhovis.htm)
- [Native Plant Trust, Go Botany: Rhododendron viscosum](https://gobotany.nativeplanttrust.org/species/rhododendron/viscosum/)
- [Alabama Cooperative Extension System: Native Azaleas, Chip East, April 15, 2020](https://www.aces.edu/blog/topics/landscaping/native-azaleas/)
- [UConn Plant Database: Rhododendron viscosum](https://plantdatabase.uconn.edu/detail.php?pid=404)

## Read before planting

- [Ten planting mistakes that quietly kill trees](https://bluewhaletrees.com/articles/ten-planting-mistakes/index.html.md)
- [Transplanting young trees: timing, water and protection](https://bluewhaletrees.com/articles/transplanting-young-trees/index.html.md)
- [Protecting young trees from voles, rabbits, deer and squirrels](https://bluewhaletrees.com/articles/protecting-trees-from-animals/index.html.md)
- [The habitat around a tree is part of the tree](https://bluewhaletrees.com/articles/habitat-around-a-tree/index.html.md)
- [Invasive vines and shrubs are what is killing your woods](https://bluewhaletrees.com/articles/invasive-vines-and-shrubs/index.html.md)
- [Native trees and shrubs for birds: caterpillars, fruit, mast, nests and winter cover, month by month](https://bluewhaletrees.com/articles/native-trees-for-birds/index.html.md)

## Related

- [Planting-site check](https://bluewhaletrees.com/tools/site-check/index.html.md): for a thrive, struggle or fail verdict on Swamp Azalea, add ?species=swamp-azalea with zone (2 to 10), sun (full, part, shade) and moisture (dry, average, wet) to that address, for example ?species=swamp-azalea&zone=4&sun=part&moisture=average.
- [Companion species for Swamp Azalea](https://bluewhaletrees.com/tools/companions/index.html.md?species=swamp-azalea): the natives that share its ground and the plants that pair with it in a yard.
- [Growth estimator](https://bluewhaletrees.com/tools/growth/index.html.md): how the height and trunk projections are made; the estimate itself runs in the browser at https://bluewhaletrees.com/tools/growth/#species=swamp-azalea
- [Seed sowing planner](https://bluewhaletrees.com/tools/sowing/index.html.md): how Swamp Azalea is sown, in the chart for every species (treatment, cold days, depth, timing); the dated plan runs in the browser at https://bluewhaletrees.com/tools/sowing/#species=swamp-azalea
- [Pollination planner](https://bluewhaletrees.com/tools/pollination/index.html.md): what Swamp Azalea needs for a crop and how many to plant, in the table for every species; the planner runs in the browser at https://bluewhaletrees.com/tools/pollination/#plants=swamp-azalea:1
- [Bloom and fruit calendar](https://bluewhaletrees.com/tools/calendar/index.html.md): the months Swamp Azalea flowers and fruits, in the grid for every species.