Cunningham's White Rhododendron
Rhododendron 'Cunningham's White'
Ericaceae · broadleaf evergreen shrub · introduced
Last updated
A dense, compact, spreading evergreen shrub reaching 4 feet in 10 years and up to 10 feet at maturity. Funnel-shaped white flowers with fine yellowish-green to brown speckling on the upper lobe, 2 to 2⅜ inches wide; flower buds are pink before opening. Dome-shaped trusses. Midseason bloom. A hybrid of R. caucasicum crossed with white-flowered R. ponticum, bred by Cunningham in 1850 (RHS 58). OSU rates flower quality 2, plant and foliage 3, and performance 4 on a 1-5 scale.
The toughest ironclad rhododendron in common cultivation. Tolerates slightly alkaline soil and urban air pollution better than nearly any other rhododendron, a trait inherited from its caucasicum and ponticum parents. Hardy to -15°F (Zone 5b-9a). Full sun to part shade on acidic to near-neutral soil (pH 4.5-6.0). The lower flower quality rating (2/5 OSU) reflects modest individual bloom size and lax truss form, but the plant is virtually indestructible once established. Twenty-one diseases and 15 pests documented at the genus level. All parts contain grayanotoxins and are toxic if ingested.
Quick Facts
Root Colonization (Spring–Fall)
Infection at Bud Break
Apothecia Formation & Spore Release
Aecial Stage (Alternate Host)
+ 13 more — see full disease and pest lists below
Phenological Calendar
| Stage | Typical Window |
|---|---|
| Bud swell BBCH 01-03 | Mar 15-Apr 15 |
| Bloom start BBCH 61 | Apr 25-May 10 |
| Full bloom BBCH 65 | May 1-May 18 |
| Bloom end BBCH 69 | May 15-Jun 1 |
| Bud set BBCH 55-59 | Jul 15-Sep 15 |