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Journal American Rhododendron Society

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Dr. Glen Jamieson ars.editor@gmail.com


Volume 24, Number 3
July 1970

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A Survey of Rhododendron Species of Washington, D.C. and Vicinity
Richard T. Johnston

        U. S. National Arboretum, Washington, D.C. The object of this survey was to compile a list of rhododendron species growing in Washington, D.C. and vicinity, and to obtain some evaluation of success based on the experience of those persons growing them. Information was collected on 184 species in 24 collections by means of a questionnaire or interview. It is based on growers' experiences in private gardens and in the U.S. National Arboretum, the majority of gardens being found inside of the area encircled by the Capitol Beltway 1495.
        Table 1 lists species together with the number of locations, the total number of plants found in these gardens, age and/or size of the plants, the growers' evaluation of performance, and general comments. These comments where given represent a summary or condensed statement.
        Table 2 lists species being grown but as yet unevaluated due to a lack of sufficient exposure.

Table 1: Rhododendron species being grown in Washington D.C. and vicinity.

Species Number of
Locations1
Number of
Plants2
Age or Size3 Performance4 Comments
aberconwayi 5 6 2' S best bloom '69
adenophorum 1 1 3yr / 1' P apparently hardy
adenopodum 6 8 l1yr S needs sun to bloom
alabamense 3 3 15yr S likes sun
albrechtii 5 12+ 5' S  
ambiguum 2 3 1' U winter killed
arborescens 6 8 l5yr / 8' S fragrant
arboreum 3 40 3yr / 2' P terminal dieback each year
argyrophyllum   1 2' P hardy in foliage; no buds yet
arizelum 1 1 2yr U heat killed
artosquameum 1 2 2yr / 1' U winter killed, perhaps frost heaving
atlanticum 4 6 35yr S suckers forming colonies: very fragrant
augustinii 8 29 5' S not reliably hardy
auriculatum 4 10 10' S slow starter
auritum 2 3 2' U winter killed
austrinum 4 7 16yr / 8' S  
bakeri 6 8+ 15yr S mountain plant; slow growth and color loss here
barbatum 3 3 4yr / 2' P  
brachycarpum 7 16+ 5yr P interesting foliage
bureavii 2 32 2yr / 6" U heat killed
calendulaceum 12 48 15' S excellent. but few flowers in shade
calophytum 5 6 9yrs P very slow growth but good foliage
caloxanthum 1 1 1' U summer death
campanulatum 3 4 1' P appears hardy
campylocarpum 6 17 6' S likes shade
campylogynum 1 1 4yr / 6" U many branches die back
canadense 3 13 1' P  
canescens 2 2 2' P  
carolinianum 16 150+ 17yr S good drainage vital, bronze winter leaves
catawbiense 13 300+ 30yr / 15' S tolerant of soils and exposure; borers experienced
var. album 3 40 8yr / 4' S best in sun
caucasicum 5 8 5' S slow grower, long time to bloom: root rot and caterpillars experienced
var. hidakanum 1 2 1' P O.K. winter '69
chaetomallum 1 1 6" U heat killed
chapmanii 6 14 2' S hard to establish
chrysanthum 5 8 4yr / 8" P slow growth
cinnabarinum 1 2 4' S  
concatenans 2 3 1' U winter killed
concinnum 3 5+ 2' P appears hardy
crassum 2 2 1' U heat killed
dauricum 5 25+ 30yr S white forms excellent
davidsonianum 3 39 3yr / 2' P  
decorum 9 50+ 12' S very adaptable
degronianum 5 15+ 5' S  
desquamatum 2 15+ 4yr / 2' P grows well, appears hardy
diaprepes 2 2+ 2' U never healthy
dichroanthum 1 1 4' P  
dictyotum 1 1 6" U winter killed
discolor 9 75+ 5' S  
erubescens 1 1 4yr / 2' P  
fargesii 4 5 5' S a heavy bloomer
farrerae 1 1 2' U winter killed
fastigiatum 2 3+ 1' U winter killed, perhaps frost heaving
fauriei 4 12+ 2' P  
ferrugineum 4 5 1' P  
flavidum 1 1 6" P  
flavum 5 9 15yr / 8' S needs sun to bloom
forrestii 2 3 6yr S  
fortunei 14 600+ 20' S vigorous, adaptable, profuse bloom
galactinum l 1 2' P  
griersonianum 3 18+ 4' U winter killed
haemaleum 1 2 14yr S  
haematodes 3 4 1' U winter kill and root rot
hanceanum 2 2 4yr / 1' P survives winter only with protection
hemsleyanum 2 2+ 4yr / 3' P  
hippophaeoides 4 6 13yr S quite hardy, blooms in spring and fall
hirsutum 4 3+ 1' U winter killed
houlstonii 3 12 7yr / 3' S  
hyperythrum 3 5+ 1' P plastic winter protection
impeditum 10 120+ 1' S excellent in full sun and dry soil
indicum 3 10 15yr S good here
intricatum 1 1 1' U winter killed
irroratum 2 5 3yr / 2' P  
japonicum 6 5 l0yr / 4' S best on clay loam
kaempferi 3 12 15yr S  
keiskei 12 153 14yr S needs shade and wind break; slow starter
keleticum 3 3+ 1' P survived with plastic windbreak, others winter killed
kiusianum 4 5+ 3yr / 2' S  
kotschyi 2 4 8yr S slow starter
laciniatum 2 3 2yr / 18" S  
lepidotum 1 1 1' U heat killed
leucaspis 1 1 6" U not hardy
litiense 4 27+ 5yr / 18" P hardy with protection
lutescens 4 4 4yr / 4' P  
makinoi 9 15+ 13' S very hardy, likes sun to bloom
mallotum 2 2+ 1' P  
maximum 10 1000+ 20yr S withstands neglect
var. rubrum 1 1 6yr / 3' S  
metternichii 11 17+ 2-1/2' S likes sun to bloom
micranthum 5 6 14yr S spiraea-like flowers
minus 9 38 5' S hardy, but root rot and lacefly experienced
molle 5 13 15yr S powdery mildew experienced
mucronatum 4 15+ 20yr / 8' S whitefly in sun
muctonulatum 14 200+ 30yr S early flowers frost 2 years of 3
nipponicum 1 2 1' U heat killed
nudiflorum 6 41 25yr / 6' S likes sun and drainage; native here
obtusum 1 3 10yr S O.K. but slow
occidentals 3 11 3yr / 2' P powdery mildew experienced
oldhamii 1 1 10yr S  
orbiculare 4 12 1' P foliage turns red in fall
oreotrephes 4 5 3' P red winter foliage
ovatum 1 1 1' P  
pentaphyllum 2 3 1' P  
polylepis 1 5 7yr / 2' P one flower '69
pomense 1 2 2yr / 8" P  
ponticum 2 13 5' S  
poukhanense 4 12 15yr / 3' S  
prunifolium 7 10+ 15yr S beautiful, blooms
pseudochrysanthum 2 1+ 1' P  
pubescens 3 4+ 4yr / 2' S  
pulchrum 2 4 12yr S does well
puralbum 3 7+ 6' S profuse bloom
racemosum 12 150+ 4' S variable hardiness
reticulatum 5 6 15yr / 5' S poor flower color
rex 4 2+ 18" P needs winter protection
roseum 5 6 4' S root rot experienced
rubiginosum 4 6 6' S profuse bloom
rude 1 1 l' U heat killed
russatum 3 2+ 15" S  
sanctum 1 l 3yr / 15" P slight winter damage
sargentianum 1 1 6" U heat killed
schlippenbachii 10 127 15yr / 12' S slow starter, leaves burn in bright sun
scintillans 1 1 4yr / 2' P  
scyphocalyx 1 1 9" U winter killed
searsiae 1 1 3' S  
serpyllifolium 3 3 3yr / 18" S  
serrulatum 4 5 6" S  
simsii 3 3 2' S  
var. eriocarpum 1 12 10yr S outstanding dwarf, does well here
smirnowii 7 13 12yr S  
souliei 4 3+ 1' U winter killed
spiciferum 2 2 4yr / 2' S  
stewartianum 3 4 4' P  
strigillosum 3 2+ 4yr / 18" P  
sutchuenense 6 27 5yr / 2' P  
taliense 2 3 2yr / 8" P  
tapetiforme 1 1 2yr U heat killed
thayerianum 3 2+ 6yr P  
trichophorum 1 1 4yr / 1' P  
triflorum 2 2 2yr / 2' P leggy
vaseyi 7 12 30yr S needs sun to bloom
vernicosum 8 17 14yr S  
verruculosum 1 1 2yr / 1' P  
viscosum 7 19+ 4yr / 3' S needs sun to bloom
wardii 8 25+ 4yr / 3' P not reliably hardy
weyrichii 4 50+ 5' S profuse bloom
wightii 4 5+ 1' U winter killed
williamsianum 4 15 5yr / 2’ P winters only with protection; root rot experienced
wilsonae 2 22 5yr S likes sun, very hardy
xanthocodon 2 4 3' P  
yakushimanum 11 64+ 8yr / 1' S very slow grower, but performs well even exposed to N.W. sun and wind
yunnanense 7 23 5yr / 2' S winter kill and root rot reported but a few doing O.K.
1 number of separate gardens or collections in which species is found.
2 total number of plants found; + indicates young seedlings or cuttings
3 age in years of oldest plant if known, otherwise largest size in feet or inches.
4 performance: S - satisfactory plant and flower; P - satisfactory plant, no flowers as yet;
               U - unsatisfactory (poor development or lack of tolerance).

       

Table 2: Species being grown but as yet unevaluated due to a lack of sufficient exposure.
amagianum, anthopogon, balfourianum, brachyanthum, bullatum, callimorphum, camtschaticum, chartophyllum, chlorops, chryseum, ciliatum, clementinae, crinigerum, decandrum, elliottii, fictolacteum, fulgens, fulvum, glaucophyllum, glomerulatum, grande, gymnocarpum, habrotrichum, hemitrichotum, linearifolium, macabeanum, maddenii, magorianum, manipurense, nakaharai, neriiflorum, oleifolium, pemakoense, planetum, praevernum, prattii, quinquefolium, sinogrande, sinogrande var. boreale, tephropeplum, thomsonii, titeum, tschonoskii, ungernii, xanthostephanum

        Judges were Walter Eickhorst and Roy Nordine of Morton Arboretum. Most of the members visited the plantings in the arboretum. These are now coming into good bloom and are creating quite a spectacle. The plantings are on a gravelly hill under tall pines, The slope of the hill is to a road and the plants have developed to sizes where they are becoming quite showy.
        While the show was better this year than previous ones it would have been much better except for the weather which was extremely hot and dry and turned wet with severe thunderstorms. The heat and rain between them injured many trusses that otherwise would have been in the show.


Volume 24, Number 3
July 1970

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