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Azalea Rhododendron

Other Common Name(s):

Previously known as:

  • Azaleastrum
  • Biltia
  • Ledum
  • Rhodora
Phonetic Spelling
rho-doh-DEN-dron
This plant has high severity poison characteristics.
See below
Description

Every year spring is ushered in with the colorful blooms of azaleas and rhododendrons in North Carolina. Home gardens and botanical gardens display red, pink, white, orange, and lavender blooms of azaleas. In western North Carolina displays of lavender or white rhododendrons are seen along the Blue Ridge Parkway. 

In the genus Rhododendron, there are more than 1000 species that include both rhododendrons and azaleas which are both woody and spring flowering shrubs. Some of the shrubs also have attractive winter foliage while others lose their leaves. This can be a bit confusing. Most of the plants are evergreen but some are deciduous.

This genus is divided into subgenera of evergreen rhododendrons, deciduous rhododendrons, evergreen azaleas, and deciduous azaleas. Rhododendrons maybe 6 to 10 feet tall and 5 to 8 feet wide, but azaleas tend to be smaller. They are members of the Ericaceae or blueberry family which also includes mountain laurels, heathers, cranberries, and blueberries.

Rhododendrons are native to Asia, Europe, and North America. The rhododendron species are found growing in the wild in many parts of the world. The evergreen species are native to Asia while the deciduous species are native to the United States. There are many cultivars and varieties. Some are native to North Carolina. There are about 15 species that are native to the southeastern United States.

The genus name, Rhododendron, is derived from two Greek words, rhodo which means "rose," and dendron which means "tree." 

Azaleas and rhododendrons thrive in acidic soils and prefer filtered sunlight. They need protection from the afternoon sun to prevent leaf scorch. Their roots are shallow, and they prefer moist, well-drained, rich organic soils. They should be watered by a soaker hose or irrigation in dry weather.  Foliage diseases can occur from overhead watering or sprinklers. They do not tolerate dense clay due to water retention and compaction. If you have clay soil, amend it with organic material. The roots may rot if the soil does not drain well. Plant the root ball high in the soil to help with drainage issues. Mulch will help keep the root ball cool and moist. Avoid overwatering and over-fertilizing. Pruning, if desired, may be done after flowering. They can be propagated by seed, stem cutting, layering, or grafting.

Azaleas and rhododendrons are at home as understory shrubs planted in groups in woodland or naturalized areas, or as specimens in pollinator gardens where the flowers will attract hummingbirds and bees. Some varieties are grown as houseplants. 

Seasons of Interest:

Bloom:  Spring                  Foliage:  Spring and Summer

Per the American Rhododendron Society, "All azaleas are rhododendrons, but not all rhododendrons are azaleas." Here are some general characteristics to differentiate the two:

Quick ID Hints for Azaleas:

  • bloom in April
  • tubular or funnel-shaped flowers
  • one flower per stem but has many stems that make the shrub look like it is covered in blooms
  • 5 lobes per flower
  • 5 stamens
  • multiple bloom colors including white, cream, pink, red, lavender, purple, orange, and yellow
  • foliage elliptical to obovate, thin, small, entire margins, thick pubescence, cluster at the tips of the branch, buds are smaller
  • most are deciduous but there are many evergreens

Quick ID Hints for Rhododendrons:

  • bloom later in the spring
  • bell-shaped flowers
  • blooms grow in clusters at the end of the branch
  • 5 lobes per flower 
  • 10 stamens 
  • blooms are typically white, pink, purple, red, and rarely yellow
  • leaves are green elliptic, entire margins, thick, leathery, glossy, undersides may be scaly or have small dots
  • terminal clusters of dried capsules release seeds

Insects, Diseases, and Other Plant Problems: Insect problems include aphids, borers, lace bugs, leafhoppers, mealybugs, spider mites, nematodes, scale, thrips, and whitefly. Diseases include leafy gall, canker, crown rot, root rot, leaf spot, rust, and powdery mildew. This plant is frequently damaged by deer. Chlorosis or yellowing of the leaves can occur if there is an iron deficiency in the soil.

While these shrubs remain very popular for landscape use, many cultivars are susceptible to Phytophthora root rot– this leads to leaf loss, reduced vigor, branch dieback, and wilting.  Implement good cultural practices first, such as improving drainage with organic matter or berms and avoiding overwatering or overfertilization.  However, if you have a site with a history of this disease, consider planting one of the root rot-resistant alternative species listed in the left-hand sidebar.

For suitable alternatives, see this video created by Charlotte Glen as part of the Plants, Pests, and Pathogens series.

VIDEO Created by Elizabeth Meyer for "Trees, Shrubs and Conifers" a plant identification course offered in partnership with Longwood Gardens.

Profile Video:
See this plant in the following landscapes:
Wild Side- A Shady Garden Woodland Walk Wild Side- A Shady Garden Woodland Backyard Garden Walk Juniper Level Botanic Gardens: Part Sun-Part Shade Gardens Woodland Walk Juniper Level Botanic Gardens: Front Shade Garden Woodland Backyard Garden Walk Juniper Level Botanic Gardens: Part Sun-Part Shade Gardens Flower Bonanza Garden Woodland Backyard Garden Walk Juniper Level Botanic Gardens: Front Shade Garden Woodland Backyard Garden Walk Back of House Planting Flower Bonanza Garden Woodland Walk Coastal Entryway Garden Rock & Water Garden
Cultivars / Varieties:
'Aubie', 'Dr. A. Blok', Encore® Series, 'Girard's Crimson', 'Golfer', 'Graziella', 'High Tide', 'Knaphill and Exbury Azaleas', 'Mandarin Lights - Northern Light' Hybrid, 'Maximum', 'Nancy of Robin Hill', Pale Moon, PJM Group, R. alabamense, 'Ramapo', R. arborescens, R. atlanticum, R. austrinum, R. calensulaceum, R. canescens, R. catawbiense, R. cumberlandense, R. eriocarpum, R. flammeum, R. impeditum, R. indicum, R. kaempferi, R. maximum, R. minus, R. mucronulatum, 'Roseum-Elegans', R. periclymenoides, R. ponticum, R. prunifolium, R. roseum, R. schlippenbachii, R. vaseyi, R. viscosum, R. yakushimanum, 'Silver Bear', Southern Indica Hybrids, 'Strawberry Ice', 'Vibrant Violet Azalea', 'Windbeam', x bakeri 'Clyo Red', x hybridum 'Glenn Dale', x hybridum 'Gunrei Satzuki', x 'Stonewall Jackson'
Tags:
#evergreen#showy flowers#deciduous#poisonous#houseplant#specimen#slow growing#nectar plant#native bees#woody#low maintenance#tsc#dappled shade#specialized bees#cpp#deer browsing plant#naturalizes#screening#pollinator plant#leathery leaves#understory planting#understory shrub#problem for cats#tsc-s#problem for dogs#bee friendly#problem for horses#shrub borders#woodland garden#container plant#landscape plant sleuths course
 
Cultivars / Varieties:
'Aubie', 'Dr. A. Blok', Encore® Series, 'Girard's Crimson', 'Golfer', 'Graziella', 'High Tide', 'Knaphill and Exbury Azaleas', 'Mandarin Lights - Northern Light' Hybrid, 'Maximum', 'Nancy of Robin Hill', Pale Moon, PJM Group, R. alabamense, 'Ramapo', R. arborescens, R. atlanticum, R. austrinum, R. calensulaceum, R. canescens, R. catawbiense, R. cumberlandense, R. eriocarpum, R. flammeum, R. impeditum, R. indicum, R. kaempferi, R. maximum, R. minus, R. mucronulatum, 'Roseum-Elegans', R. periclymenoides, R. ponticum, R. prunifolium, R. roseum, R. schlippenbachii, R. vaseyi, R. viscosum, R. yakushimanum, 'Silver Bear', Southern Indica Hybrids, 'Strawberry Ice', 'Vibrant Violet Azalea', 'Windbeam', x bakeri 'Clyo Red', x hybridum 'Glenn Dale', x hybridum 'Gunrei Satzuki', x 'Stonewall Jackson'
Tags:
#evergreen#showy flowers#deciduous#poisonous#houseplant#specimen#slow growing#nectar plant#native bees#woody#low maintenance#tsc#dappled shade#specialized bees#cpp#deer browsing plant#naturalizes#screening#pollinator plant#leathery leaves#understory planting#understory shrub#problem for cats#tsc-s#problem for dogs#bee friendly#problem for horses#shrub borders#woodland garden#container plant#landscape plant sleuths course
  • Attributes:
    Genus:
    Rhododendron
    Family:
    Ericaceae
    Uses (Ethnobotany):
    The species has been used in traditional medicine to treat pain, gastrointestinal problems, asthma, colds, and skin diseases. They are toxic and have all been used as poison.
    Life Cycle:
    Woody
    Recommended Propagation Strategy:
    Grafting
    Layering
    Seed
    Stem Cutting
    Country Or Region Of Origin:
    Northern Hemisphere to Tropical Asian Mountains and NE Australia
    Distribution:
    Native: most of the United States except AZ, IA, IN, NE, ND, and SD. Native: Europe, Asia, and NE Australia. Introduced: Belgium, Great Britain, Ireland, Madeira, and the Netherlands.
    Wildlife Value:
    Flowers attract humingbirds. Members of the genus Rhododendron support the following specialized bee: Andrena (Andrena) cornelli. Deer browse this plant.
    Play Value:
    Attractive Flowers
    Colorful
    Dimensions:
    Height: 6 ft. 0 in. - 10 ft. 0 in.
    Width: 5 ft. 0 in. - 8 ft. 0 in.
  • Whole Plant Traits:
    Plant Type:
    Houseplant
    Native Plant
    Poisonous
    Shrub
    Woody Plant Leaf Characteristics:
    Broadleaf Evergreen
    Deciduous
    Habit/Form:
    Rounded
    Growth Rate:
    Slow
    Maintenance:
    Medium
  • Cultural Conditions:
    Light:
    Dappled Sunlight (Shade through upper canopy all day)
    Deep shade (Less than 2 hours to no direct sunlight)
    Partial Shade (Direct sunlight only part of the day, 2-6 hours)
    Soil Texture:
    High Organic Matter
    Loam (Silt)
    Sand
    Soil pH:
    Acid (<6.0)
    Soil Drainage:
    Good Drainage
    Moist
    Available Space To Plant:
    12 inches-3 feet
    3 feet-6 feet
    6-feet-12 feet
    12-24 feet
    NC Region:
    Coastal
    Mountains
    Piedmont
    USDA Plant Hardiness Zone:
    4a, 4b, 5b, 5a, 6a, 6b, 7b, 7a, 8b, 8a
  • Fruit:
    Fruit Color:
    Brown/Copper
    Red/Burgundy
    Display/Harvest Time:
    Fall
    Fruit Type:
    Capsule
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    A terminal cluster of dried red-brown capsules, 1/2" long, appears in fall and releases seeds.
  • Flowers:
    Flower Color:
    Gold/Yellow
    Orange
    Pink
    Purple/Lavender
    Red/Burgundy
    White
    Flower Inflorescence:
    Raceme
    Flower Value To Gardener:
    Showy
    Flower Bloom Time:
    Spring
    Flower Shape:
    Bell
    Funnel
    Tubular
    Flower Size:
    1-3 inches
    Flower Description:
    Azalea blooms are tubular or funnel-shaped. Rhododendron blooms are bell-shaped. They are both 5 lobed. Azaleas flower on many stems like an umbrella. Rhododendrons bloom in clusters. Azaleas bloom in April and have 5 stamens, and rhododendrons bloom later in the spring and have 10 stamens. Azaleas bloom in pink, red, orange, yellow, white, purple, and lavender. Rhododendrons bloom in pink, red, purple, and white, and rarely yellow.
  • Leaves:
    Woody Plant Leaf Characteristics:
    Broadleaf Evergreen
    Deciduous
    Leaf Color:
    Green
    Leaf Feel:
    Glossy
    Leathery
    Leaf Type:
    Simple
    Leaf Arrangement:
    Alternate
    Leaf Shape:
    Elliptical
    Lanceolate
    Oblanceolate
    Obovate
    Ovate
    Leaf Margin:
    Entire
    Hairs Present:
    Yes
    Leaf Length:
    3-6 inches
    Leaf Width:
    1-3 inches
    Leaf Description:
    The leaves may be evergreen or deciduous. Azaleas leaves are small, thin, elliptic, and obovate with entire margins. They are also thickly pubescent and cluster at the tips of the branches. Rhododendron leaves are laurel-like, green elliptic with entire margins, thick, leathery, glossy, and cluster at the end of the stem.
  • Bark:
    Surface/Attachment:
    Peeling
    Shredding
    Bark Description:
    The bark is thin and sometimes peels or shreds.
  • Stem:
    Stem Color:
    Gold/Yellow
    Gray/Silver
    Stem Is Aromatic:
    No
    Stem Description:
    The stems may be erect, creeping, or prostrate, and they may be smooth or hairy. Leaf buds are small, flower buds are larger and shaped like eggs, gray to yellowish
  • Landscape:
    Landscape Location:
    Container
    Naturalized Area
    Patio
    Woodland
    Landscape Theme:
    Asian Garden
    Shade Garden
    Design Feature:
    Border
    Hedge
    Mass Planting
    Screen/Privacy
    Small groups
    Specimen
    Attracts:
    Hummingbirds
    Pollinators
    Specialized Bees
    Resistance To Challenges:
    Rabbits
    Problems:
    Poisonous to Humans
    Problem for Cats
    Problem for Dogs
    Problem for Horses
  • Poisonous to Humans:
    Poison Severity:
    High
    Poison Symptoms:
    Salivation, watering of eyes and nose, abdominal pain, loss of energy, depression, nausea and vomiting, diarrhea, weakness, difficult breathing, progressive paralysis of arms and legs, cardiac failure, coma.
    Poison Toxic Principle:
    Andromedotoxin, Grayantoxin
    Causes Contact Dermatitis:
    No
    Poison Part:
    Bark
    Flowers
    Fruits
    Leaves
    Roots
    Sap/Juice
    Seeds
    Stems