Capistrano Rhododendron

Rhododendron 'Capistrano'

Ericaceae · broadleaf evergreen shrub · introduced

Last updated May 12, 2026

A dense, mounding evergreen shrub reaching 4 feet in 10 years and 5 to 7 feet at maturity. Frilly, funnel-campanulate flowers are pale greenish-yellow with no markings, carried in dome-shaped trusses of 15 blooms. Midseason flowering. Complex hybrid parentage involving 'Hindustan' and multiple fortunei and catawbiense crosses; bred by David Leach (ARS 972).

Exceptional cold hardiness for a yellow elepidote: rated to -15°F (Zone 5b-8b), making it usable in zones where most yellow rhododendrons fail. Best flower color develops in part shade; full sun positions fade the yellow and can scorch foliage. Acidic, well-drained soil (pH 4.5-6.0). 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 ft in 10 years

Spread

4-5 ft

Growth Rate

Slow to moderate

Size at 20 yr

5-7 ft

Lifespan

Long-lived

Site Requirements

Light

Part shade (afternoon shade required)

Soil Drainage

Well Drained

Soil pH

4.5-6.0

Water

Moderate

Drought Tolerance

Moderate

Hardiness

Zones 5b–8b

Ornamental Interest

Bloom Time

Apr 25-May 10

Origin

Hybrid: 'Hindustan' × ({[Catawbiense Album × (fortunei ssp

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 25-May 10	First trusses opening on the plant
Full bloom BBCH 65	May 1-May 18	Peak display; plant covered in flowering trusses
Bloom end BBCH 69	May 15-Jun 1	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.