JARS v38n4 - Freezing Resistance of Rhododendron and Azalea

Freezing Resistance of Rhododendron and Azalea
A. Sakai, Corvallis, OR

Editor's Note:
The following tabulations were received from Mr. Sakai shortly before his return to Japan. These lists should be of interest not only to hybridizers but also to almost anyone who grows rhododendrons or azaleas in borderline hardy areas.

It is interesting to note that not all plants are similar in their cold resistance as applied to all of their plant parts. In Table 1 R. discolor and R. barbatum show a remarkable uniformity to cold resistance for all their plant parts. Whereas in Table 2 R. intricatum has a very wide ranging sensitivity to cold, depending on which plant parts are being studied. In Table 3 the flower bud of R. mucronatum is even slightly more resistant to cold than the leaf.

Table 1. Freezing Resistance of Rhododendron
Table 1. Freezing Resistance of Rhododendron	undefined Freezing Resistance (°C)					undefined
Table 1. Freezing Resistance of Rhododendron Species (Series)	undefined Flower Bud	undefined Leaf	undefined Vegetative Bud	undefined Cortex	undefined Xylem	undefined Distribution
Table 1. Freezing Resistance of Rhododendron R. brachycarpum (?)	undefined -30	undefined -60	undefined -60	undefined -60	undefined -35	undefined C.N. Japan
Table 1. Freezing Resistance of Rhododendron R. catawbiense (?)	undefined -30	undefined -60	undefined -60	undefined -60	undefined -40	undefined N.E. USA
Table 1. Freezing Resistance of Rhododendron R. dauricum (P)	undefined -30	undefined -50	undefined -60	undefined -60	undefined -40	undefined N.E. Asia, E. Siberia
Table 1. Freezing Resistance of Rhododendron R. maximum (?)	undefined -25	undefined -60	undefined -60	undefined -60	undefined -35	undefined N.E. USA
Table 1. Freezing Resistance of Rhododendron R. metternichii var. hondoensis (P)	undefined -25	undefined -60	undefined -60	undefined -60	undefined -35	undefined C. Japan
Table 1. Freezing Resistance of Rhododendron R. carolinianum	undefined -25	undefined -40	undefined -50	undefined -50	undefined -35	undefined S.E. USA
Table 1. Freezing Resistance of Rhododendron R. metternichii var. pentamerum (P)	undefined -23	undefined -50	undefined -50	undefined -60	undefined -30	undefined C. Japan
Table 1. Freezing Resistance of Rhododendron R. metternichii (P)	undefined -23	undefined -40	undefined -50	undefined -50	undefined -27	undefined C.W. Japan
Table 1. Freezing Resistance of Rhododendron R. metternichii var. yakushimanum (?)	undefined -23	undefined -40	undefined -50	undefined -50	undefined -27	undefined Yakushima Island
Table 1. Freezing Resistance of Rhododendron R. metternichii var. augustifolium (P)	undefined __	undefined -40	undefined -50	undefined -50	undefined -27	undefined C. Japan
Table 1. Freezing Resistance of Rhododendron R. ferrugineum (F)	undefined -23	undefined -30	undefined -25	undefined -35	undefined -30	undefined Europe
Table 1. Freezing Resistance of Rhododendron R. smirnowii (?)	undefined -23	undefined -30	undefined -40	undefined -40	undefined -30	undefined Caucasus, Asia Minor
Table 1. Freezing Resistance of Rhododendron R. micranthum	undefined -23	undefined -25	undefined -30	undefined -30	undefined -25	undefined C. China
Table 1. Freezing Resistance of Rhododendron R. ponticum (?)	undefined -20	undefined -35	undefined -30	undefined -30	undefined -30	undefined Caucasus, Asia Minor
Table 1. Freezing Resistance of Rhododendron R. campylocarpum	undefined -20	undefined -25	undefined -30	undefined -25	undefined -25	undefined Nepal, Tibet
Table 1. Freezing Resistance of Rhododendron R. hodgsonii	undefined —	undefined -25	undefined -30	undefined -25	undefined -25	undefined Nepal (3900m)*
Table 1. Freezing Resistance of Rhododendron R. wallichii (C)	undefined -20	undefined -28	undefined -30	undefined -30	undefined -25	undefined Nepal (3900m)*
Table 1. Freezing Resistance of Rhododendron R. campanulatum (C)	undefined -20	undefined -25	undefined -30	undefined -30	undefined -25	undefined Nepal (3900m)*
Table 1. Freezing Resistance of Rhododendron R. macrophyllum (P)	undefined -20	undefined -20	undefined -25	undefined -25	undefined -20	undefined British Columbia
Table 1. Freezing Resistance of Rhododendron R. discolor (F)	undefined -18	undefined -20	undefined -20	undefined -20	undefined -20	undefined Szechwan
Table 1. Freezing Resistance of Rhododendron R. barbatum	undefined -18	undefined -18	undefined -18	undefined -18	undefined -18	undefined Nepal (3000m)*
Table 1. Freezing Resistance of Rhododendron R. fortunei (F)	undefined -15	undefined -18	undefined -25	undefined -23	undefined -23	undefined C. China
Table 1. Freezing Resistance of Rhododendron R. griffithianum (F)	undefined -15	undefined -18	undefined -20	undefined -18	undefined -18	undefined Nepal
Table 1. Freezing Resistance of Rhododendron R. rubropunctatum	undefined -15	undefined -20	undefined -20	undefined -20	undefined -20	undefined Formosa (2000m)*
Table 1. Freezing Resistance of Rhododendron R. arboreum var. cinnamomeum (A)	undefined -13	undefined -13	undefined -13	undefined -13	undefined -13	undefined Nepal (2800m)*
Table 1. Freezing Resistance of Rhododendron R. arboreum var. campbelliae (A)	undefined -10	undefined -10	undefined -10	undefined -10	undefined -10	undefined Nepal (2200m)*
Table 1. Freezing Resistance of Rhododendron *Altitude of collection site. (P) Ponticum, (F) Fortunei, (C) Campanulatum, (A) Arboreum, (F) Ferrugineum

Table 2. Freezing Resistance of Dwarf Rhododendron
Table 2. Freezing Resistance of Dwarf Rhododendron	undefined Freezing Resistance (°C)					undefined
Table 2. Freezing Resistance of Dwarf Rhododendron Species (Series)	undefined Flower Bud	undefined Leaf	undefined Vegetative Bud	undefined Cortex	undefined Xylem	undefined Distribution
Table 2. Freezing Resistance of Dwarf Rhododendron R. parvifolium (Lapponicum)	undefined -35	undefined -60	undefined -60	undefined -60	undefined -50	undefined N.E. Asia, E. Siberia
Table 2. Freezing Resistance of Dwarf Rhododendron R. aureum	undefined -25	undefined -60	undefined -60	undefined -60	undefined -50	undefined C.N. Japan
Table 2. Freezing Resistance of Dwarf Rhododendron R. impeditum (Lapponicum)	undefined -25	undefined -50	undefined -50	undefined -50	undefined —	undefined Yunnan (33-3900m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. dasypetalum (Lapponicum)	undefined -25	undefined -50	undefined -50	undefined -50	undefined -35	undefined Yunnan (32-4000m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. anthopogon (Anthopogon)*	undefined -23	undefined -50	undefined -50	undefined -50	undefined -50	undefined E. Nepal (27-4800m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. setosum (Lapponicum)*	undefined -23	undefined -50	undefined -50	undefined -50	undefined -50	undefined E. Nepal (33-4800m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. fastigiatum (Lapponicum)	undefined -24	undefined 40	undefined -40	undefined -40	undefined -30	undefined Yunnan (31-4100m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. intricatum (Lapponicum)	undefined -23	undefined -35	undefined -40	undefined -50	undefined -35	undefined Szechwan (36-4500m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. keiskei (Triflorum)	undefined -23	undefined -25	undefined -30	undefined -30	undefined -25	undefined Japan
Table 2. Freezing Resistance of Dwarf Rhododendron R. scintillans (Lapponicum)	undefined -20	undefined -40	undefined -40	undefined -40	undefined -35	undefined Yunnan (33-4-200m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. russatum (Lapponicum)	undefined -20	undefined -40	undefined -40	undefined -40	undefined -30	undefined Yunnan (33-4000m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. lepidotum (Lapponicum)*	undefined -20	undefined -40	undefined -30	undefined -60	undefined -30	undefined E. Nepal (24-4500m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. russatum (Lapponicum)	undefined -20	undefined -40	undefined -40	undefined -40	undefined -30	undefined Yunnan (33-4000m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. fimbriatum (Lapponicum)	undefined -20	undefined -35	undefined -35	undefined -25	undefined -25	undefined Szechwan (3600m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. keiskei var. hypoglaucum (Triflorum)	undefined -20	undefined -25	undefined -25	undefined -35	undefined -35	undefined Japan
Table 2. Freezing Resistance of Dwarf Rhododendron R. radicans (Saluenense)	undefined -15	undefined -25	undefined -25	undefined -25	undefined -25	undefined S.E. Tibet (42-4500m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. racemosum (Scabrifolium)	undefined -17	undefined -15	undefined -18	undefined -18	undefined -18	undefined Yunnan (17-3700m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. hanceanum (Triflorum)	undefined -15	undefined -20	undefined -20	undefined -20	undefined -20	undefined Szechwan (5-3000m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. yunnanense (Triflorum)	undefined -15	undefined -18	undefined -20	undefined -25	undefined -25	undefined S.E. Tibet (22-3000m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. augustinii (Triflorum)	undefined -15	undefined -15	undefined -20	undefined -20	undefined -20	undefined Yunnan (18-2700m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. hippophaeoides (Lapponicum)	undefined -15	undefined -15	undefined -25	undefined -25	undefined -25	undefined Yunnan (33-3400m)
Table 2. Freezing Resistance of Dwarf Rhododendron R. amamiosimense	undefined -13	undefined -15	undefined -13	undefined -17	undefined -17	undefined Japan (Amami Island) 800m
Table 2. Freezing Resistance of Dwarf Rhododendron * Collected at East Nepal (3900m alt.)			undefined	undefined	undefined	undefined

Table 3. Freezing Resistance of Azalea
Table 3. Freezing Resistance of Azalea	undefined Freezing Resistance (°C)					undefined
Table 3. Freezing Resistance of Azalea Species	undefined Flower Bud	undefined Leaf	undefined Vegetative Bud	undefined Cortex	undefined Xylem	undefined Distribution
Table 3. Freezing Resistance of Azalea R. mucronulatum Turcz.	undefined -30	undefined —	undefined -60	undefined -60	undefined -40	undefined China, Korea, Japan
Table 3. Freezing Resistance of Azalea R. viscosum	undefined -30	undefined —	undefined -50	undefined -60	undefined -40	undefined USA (East)
Table 3. Freezing Resistance of Azalea R. arborescens	undefined -30	undefined —	undefined -40	undefined -60	undefined -40	undefined USA (East)
Table 3. Freezing Resistance of Azalea R. schlippenbachii	undefined -28	undefined —	undefined -30	undefined -30	undefined -30	undefined Korea, Japan
Table 3. Freezing Resistance of Azalea R. japonicum (A. Gray) Suringer	undefined -25	undefined —	undefined -40	undefined -50	undefined -40	undefined Japan
Table 3. Freezing Resistance of Azalea R. mucronulatum var. ciliatum Nakai	undefined -25	undefined —	undefined -50	undefined -50	undefined -35	undefined Korea, Japan
Table 3. Freezing Resistance of Azalea R. tschonoskii Maxim.	undefined -25	undefined —	undefined -40	undefined -40	undefined -40	undefined Korea, Japan
Table 3. Freezing Resistance of Azalea R. albrechtii (Maxim.)	undefined -25	undefined —	undefined -40	undefined -40	undefined -30	undefined Japan
Table 3. Freezing Resistance of Azalea R. yedoense var. poukhanense Nakai	undefined -25	undefined -30	undefined -30	undefined -30	undefined -30	undefined Korea, Japan
Table 3. Freezing Resistance of Azalea R. obtusum var. japonicum (Maxim.) Kitamura	undefined -25	undefined —	undefined -30	undefined -30	undefined -25	undefined Japan
Table 3. Freezing Resistance of Azalea R. obtusum (Planchon) (Maxim.)	undefined -23	undefined -30	undefined -30	undefined -30	undefined -30	undefined Japan
Table 3. Freezing Resistance of Azalea R. pentaphyllum var. nikoense	undefined -23	undefined —	undefined -25	undefined -30	undefined -25	undefined Japan
Table 3. Freezing Resistance of Azalea R. reticulatum D. Don	undefined -23	undefined —	undefined -30	undefined -30	undefined -30	undefined Japan
Table 3. Freezing Resistance of Azalea R. mucronatum (Blume) G. Don	undefined -23	undefined -17	undefined -25	undefined -25	undefined -25	undefined Japan
Table 3. Freezing Resistance of Azalea R. occidentale	undefined -20	undefined —	undefined -25	undefined -25	undefined -23	undefined USA (West)
Table 3. Freezing Resistance of Azalea R. macrosepalum Maxim.	undefined -20	undefined -20	undefined -25	undefined -25	undefined -27	undefined Japan
Table 3. Freezing Resistance of Azalea R. nudipes Nakai	undefined -20	undefined —	undefined -27	undefined -27	undefined -25	undefined Japan
Table 3. Freezing Resistance of Azalea R. serpyllifolium (A. Gray) Micquel*	undefined -20	undefined -25	undefined -25	undefined -25	undefined -25	undefined Japan
Table 3. Freezing Resistance of Azalea R. simsii PI.	undefined -18	undefined —	undefined -30	undefined -30	undefined -30	undefined China
Table 3. Freezing Resistance of Azalea R. ripense Makino*	undefined -15	undefined -20	undefined -20	undefined -20	undefined -20	undefined Japan
Table 3. Freezing Resistance of Azalea R. scabrum G. Don*	undefined -13	undefined -15	undefined -15	undefined -15	undefined -15	undefined S. Japan
Table 3. Freezing Resistance of Azalea R. tashiroi Maxim.*	undefined -13	undefined -15	undefined -15	undefined -15	undefined -15	undefined S. Japan
Table 3. Freezing Resistance of Azalea R. eriocarpum (Hayata) Nakai*	undefined -13	undefined -15	undefined -15	undefined -15	undefined -15	undefined S. Japan

Table 4. Freezing Resistance of Cultivars of Rhododendron
Table 4. Freezing Resistance of Cultivars of Rhododendron	undefined Freezing Resistance (°C)
Table 4. Freezing Resistance of Cultivars of Rhododendron Cultivar	undefined Flower Bud	undefined Leaf	undefined Vegetative Bud	undefined Cortex	undefined Xylem
Table 4. Freezing Resistance of Cultivars of Rhododendron Red Catawbiense Hybrid*	undefined -27	undefined -60	undefined -60	undefined -60	undefined -35
Table 4. Freezing Resistance of Cultivars of Rhododendron America*	undefined -27	undefined -50	undefined -60	undefined -60	undefined -30
Table 4. Freezing Resistance of Cultivars of Rhododendron P.J.M.**	undefined -27	undefined -50	undefined -50	undefined -50	undefined -40
Table 4. Freezing Resistance of Cultivars of Rhododendron Album Elegans*	undefined -27	undefined -40	undefined -50	undefined -50	undefined -35
Table 4. Freezing Resistance of Cultivars of Rhododendron English Roseum*	undefined -27	undefined -40	undefined -50	undefined -50	undefined -35
Table 4. Freezing Resistance of Cultivars of Rhododendron Dora Amateis**	undefined -25	undefined -40	undefined -40	undefined -40	undefined -35
Table 4. Freezing Resistance of Cultivars of Rhododendron President Lincoln*	undefined -25	undefined -40	undefined -40	undefined -40	undefined -30
Table 4. Freezing Resistance of Cultivars of Rhododendron Fastuosum Plenum*	undefined -25	undefined -35	undefined -40	undefined -40	undefined -35
Table 4. Freezing Resistance of Cultivars of Rhododendron Ramapo*	undefined -25	undefined -40	undefined -40	undefined -50	undefined -35
Table 4. Freezing Resistance of Cultivars of Rhododendron Nova Zembla	undefined -25	undefined -35	undefined -40	undefined -40	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Cheer*	undefined -25	undefined -25	undefined -30	undefined -30	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Catawbiense Grandiflorum*	undefined -24	undefined -25	undefined -30	undefined -30	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Lee's Dark Purple*	undefined -23	undefined -35	undefined -35	undefined -35	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Christmas Cheer*	undefined -23	undefined -23	undefined -25	undefined -25	undefined -20
Table 4. Freezing Resistance of Cultivars of Rhododendron Prince Camille de Rohan	undefined -20	undefined -25	undefined -35	undefined -35	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Scarlet Wonder	undefined -23	undefined -23	undefined -25	undefined -25	undefined -23
Table 4. Freezing Resistance of Cultivars of Rhododendron Blue Diamond	undefined -20	undefined -25	undefined -30	undefined -30	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Pink Pearl	undefined -20	undefined -25	undefined -25	undefined -25	undefined -20
Table 4. Freezing Resistance of Cultivars of Rhododendron Elizabeth (forrestii hybrid)	undefined -20	undefined -20	undefined -25	undefined -25	undefined -20
Table 4. Freezing Resistance of Cultivars of Rhododendron Unique (campylocarpum hybrid)	undefined -14	undefined -15	undefined -25	undefined -25	undefined -25
Table 4. Freezing Resistance of Cultivars of Rhododendron Vulcan (griersonianum hybrid)	undefined -17	undefined -20	undefined -20	undefined -20	undefined -20
Table 4. Freezing Resistance of Cultivars of Rhododendron President Roosevelt	undefined -	undefined -15	undefined -20	undefined -20	undefined -17
Table 4. Freezing Resistance of Cultivars of Rhododendron Thor	undefined -13	undefined -15	undefined -25	undefined -25	undefined -20
Table 4. Freezing Resistance of Cultivars of Rhododendron Gwen	undefined -13	undefined -13	undefined -17	undefined -17	undefined -17
Table 4. Freezing Resistance of Cultivars of Rhododendron *Catawbiense hybrid, **Carolinianum hybrid