Glacier Azalea

Rhododendron 'Glacier'

Ericaceae · broadleaf evergreen shrub · introduced

Last updated May 12, 2026

A dense, upright evergreen azalea reaching 4 to 5 feet in 10 years and 5 to 7 feet at maturity. Funnel-shaped pure white flowers with subtle dorsal spotting, 2 to 2½ inches wide, in clusters of 2 to 3 blooms. Midseason flowering. A Glenn Dale hybrid bred by Benjamin Morrison at the USDA Plant Introduction Station, drawn from R. kaempferi, R. mucronatum, and related species.

Hardy to approximately -10°F (Zone 6a-9a). Part shade to full sun on acidic, well-drained soil (pH 4.5-6.0). Glenn Dale hybrids generally tolerate higher light than Kurume types. The clean white flowers and all-green foliage (no winter bronzing) give it a quieter landscape presence than the more commonly planted colored azaleas. Twenty-one diseases and 15 pests documented at the genus level. All parts contain grayanotoxins and are toxic if ingested.

Plant Profile

Size & Form

Height

4-5 ft in 10 years

Spread

4-5 ft

Growth Rate

Moderate

Size at 20 yr

5-7 ft

Lifespan

Long-lived

Site Requirements

Light

Part Shade to Sun

Soil Drainage

Well Drained

Soil pH

4.5-6.0

Water

Moderate

Drought Tolerance

Moderate

Hardiness

Zones 6a–9a

Ornamental Interest

Bloom Time

Apr 22-May 5

Origin

Glenn Dale hybrid: parentage drawn from R. kaempferi

Cylindrocladium Blight and Root RotHigh

Root Colonization (Spring–Fall)

Leaf and Flower GallHigh

Gall Development & Sporulation

Powdery MildewHigh

Active Conidial Spread

RustHigh

Uredinial Stage (Summer)

+ 13 more — see full disease and pest lists below

Diseases: Regionally Documented (21)

Root Rot (Phytophthora spp.) Multiple obligate biotrophic fungi (Erysiphales: Erysipha... Powdery Mildew Ovulinia azaleae Ovulinia Petal Blight Lime-induced Chlorosis Symptom category — not a single disease Leaf Spot Exobasidium vaccinii Leaf and Flower Gall Cylindrocladium scoparium Cylindrocladium Blight and Root Rot Botrytis Petal Blight Multiple soilborne and waterborne pathogens cause cutting... Cutting Rots Leaf Burn Ramorum Blight (Sudden Oak Death) Botryosphaeria dothidea Botryosphaeria Dieback Seifertia azaleae Bud Blight Rhododendron necrotic ringspot virus Necrotic Ringspot Multiple genera (Melampsoridium, Thekopsora, Naohidemyces... Rust Taphrina wiesneri Witches' Broom Armillaria spp. — primarily A Armillaria Root Rot Pestalotiopsis sydowiana Gray Blight Physiological leaf spot Phytophthora Blight Tylenchorhynchus claytoni Nematode, Stunt

Pests: Regionally Documented (15)

Tetranychidae Spider mite Otiorhynchus spp. Root weevil Choristoneura rosaceana Obliquebanded Leafroller Caloptilia azaleella Azalea leafminer Stephanitis pyrioides Azalea Lace Bug Acanthococcus azaleae Azalea bark scale Aphidoidea Aphid Lepidoptera Caterpillars Parthenolecanium spp. Lecanium scale Stephanitis rhododendri Rhododendron lace bug Dialeurodes chittendeni Rhododendron whitefly Nematus lipovskyi Azalea sawfly Cacoecimorpha pronubana Carnation tortrix Icerya purchasi Cottony cushion scale Coleotechnites huntella Rhododendron bud moth

Phenological Calendar

View full calendar (5 stages)

Stage	Typical Window	What to Look For
Bud swell BBCH 01-03	Mar 15-Apr 15	Terminal flower buds enlarging; vegetative buds remain tight
Bloom start BBCH 61	Apr 22-May 5	First trusses opening on the plant
Full bloom BBCH 65	Apr 28-May 12	Peak display; plant covered in flowering trusses
Bloom end BBCH 69	May 8-May 22	Flowers fading and dropping; spent trusses brown and papery
Bud set BBCH 55-59	Jul 15-Sep 15	Distinct fat flower buds visible at branch tips by late summer; differentiated from narrow vegetative buds

Data Maturity

Baseline Extension data. Expert review underway.