QBARS - v28n1 Growing Rhododendrons in the Albany, New York Area

Growing Rhododendrons in the Albany New York Area
Hardiness Zone 5-B
Ralph H. Smith, Delmar, New York

Thirty and more years of experience have shown that rhododendrons can be grown in the Albany-New York area with success, provided some basic precautions are observed.
The problems are: subzero temperatures, frozen ground, bright sun and strong winds. Snow cover, an excellent insulator, cannot be counted on all the time. The sun's warmth on evergreen leaves starts them evaporating moisture, which the winds carry away. With frozen ground, the roots cannot replace the lost water. Leaves turn brown, dry out and die. If this is prolonged, the plant may die completely.
To prevent this, choose planting locations out of the winter sun, at least until afternoon and protected from the winter wind. The best location is in open shade; i.e., nothing overhead, but in the shadow of a building, a wooden fence, distant evergreens, or as a last resort, an open-topped burlap screen. Keep away from shallow rooted hedges or trees like the maples and beech, which will rob the rhododendrons of moisture and plant food. Plants may be set under deep-rooted oak trees, if branches are pruned high enough to walk under them and the slowly decomposing leaves keep the soil acid and well-mulched. Walnut and hickory tree roots give off toxins that result in slow death to rhododendrons.
If the soil is sandy, its moisture holding capacity must be built up by incorporating leaf mold from well-rotted oak leaves, peat moss or the well-rotted stump dirt from oaks, pines and hemlocks. If the soil is heavy clay, it is better to build beds on top of the clay, so the plants will have adequate drainage.
Protect the surface of the soil from deep freezing with a mulch of pine needles, oak leaves, or redwood or pine bark. This helps to conserve soil moisture, reduce weed growth and maintain soil acidity. Avoid fresh sawdust or wood chips, unless additional nitrogen compounds are incorporated with it. Untreated fresh sawdust will rob the plants of much needed nitrogen.
Against the occasional super-severe winter, which seems to come about once in every twenty years, the best and only protection is plants in good condition, plus the precautions taken above. Interestingly enough, it is the so-called mild winters that result in the most damage on Long Island. A series of warm days followed by sudden drops in temperature catches plants out of complete dormancy. Even the mild West Coast climate occasionally is replaced by cold blasts out of the mountains that kill plants to the ground.
One of the problems of hardiness involves early, sudden, hard freezes in the fall, before the evergreen plants are fully dormant. This frequently is the cause of loss of flower buds and sometimes of bark-splitting on the stems. Evergreen azaleas are particularly susceptible because they have not completed their growth in the fall.
What plants can be grown here with reasonable expectation that they will flower well except after that once-in-twenty-years hard winter? In general, we have to rely on the so called "Iron Clad" catawba hybrids, which evolved in western Europe over a hundred years ago. A few additional plants have shown they can take our climate, but the list is not a long one. The hardiness is derived from our native species, R. catawbiense , maximum , carolinianum and minus , while the improvement in color has come from Asiatic species.
As yet, there is no pure red-flowered rhododendron hardy in our area. The following are the best hybrids available. Varieties with an asterisk (*) are first choices:

R. 'Blue Peter'
FIG.11. Although 'Blue Peter' loses flowers
during a severe winter, its lavender blue
flowers with purple blotch survive the usual
winter in the Albany-New York area.
Photo by Cecil Smith
R. arborescens
FIG.12. The fragrant white to blush-pink
flowers of R. arborescens bloom in mid-
Photo by Fred Galle
America Lee's Dark Purple&
Nova Zembla* Purpureum Elegans
PINKS The following Rhododendron species can be
Mrs. C. S. Sargent grown with regard to some special problems:
English Roseum maximum - White flowers in early July, native
Roseum Pink to our region, but only in wooded swamps.
WHITES Slow to bloom, flowers hidden by the new
Boule de Neige* (slow growing) leaves and needs a moist site to do well.
Catawbiense album* (tall growing) catawbiense - Rosy lavender, difficult to mix
Album Elegans (tall, late) with other colors. Very hardy and a good
Beaufort foliage plant.
OTHER REDS catawbiense var. album * - White flowered selections
Atrosanguineum from the wild, as Gable's "Catalgla."
Charles Bagley dauricum - Rosy purple, deciduous, very early.
Charles Dickens

dauricum var. sempervirens - Half evergreen

Caractacus in our area.
H.W. Sargent carolinianum - Lilac pink, pink or white, small leaf early.
Dr. H. C. Dresselhuys minus - Similar to carolinianum , taller, late.

mucronulatum - Rosy purple, deciduous, very early.

Roseum Elegans Several selections in clear pink, as "Cornell Pink."
Everestianum* (frilled petals) smirnowii - Rose pink and white, leaves felted
Parson's Gloriosum underneath, slow growing.
NEW HYBRIDS, reliably hardy AZALEA HYBRIDS - Ghent (continued)
fortunei 'Mrs. Butler' - Pale pink, Gloria Mundi - Orange-red
fragrant, may lose flowers in a severe winter. Ignea Nova - Orange and pink
Pallas - Orange-red
Caroline - Pale lilac pink, fragrant Pucella - Pink
Blue Peter - Lavender blue, purple blotch, Nancy Waterer - Bright yellow. Vigorous grower.
may lose flowers in a severe winter.
HALF-HARDY SPECIES Basilisk - Deep cream, yellow flare
brachycarpum - Straw yellow to pale Berryrose - Salmon pink
pink. Leaf hardy but often loses flower buds. Cecile - Pink
caucasicum - Creamy white. Very slow. Gibraltar - Intense orange, flushed red
Hard to find. Strawberry Ice - Peach pink
degronianum - Pink and white. Leaves felted. Toucan - Creamy white. Fragrant.
keiskei - Pale yellow. Small leaves. Dwarfish. or Not Fully Tested
Hinodegiri - Red. Hardy if kept under the snow
makinoi - Pink and white. Narrow leaves. Hino-crimson - Red. Hardy if kept under the snow
sutchuenense - Large leaves, apparently mucronatum - White
leaf-hardy. No flower buds as yet. mucronatum var. amethystinum - Lilac white.
NEWER HYBRIDS - Small Leaved, Flowers below the snow line.
Fairly Hardy Rosebud - Good pink. Double.
Blue Diamond - Pale lavender blue Stewartstonian - Red.
Chesapeake - Pink and white FAILURES
Conemaugh - Lilac lapponicum - Alpine or tundra plant.
Conewago - Lavender pink Hard to duplicate proper environment.
Pioneer - Rose pink reticulatum - (Azalea dilatata) azalea
P. J. M. hybrids - Rose purple with pink flowers
Purple Gem - Bright violet racemosum - Barely survives.
Ramapo - Bright violet discolor - Large leaves. Almost hardy.
Windbeam - Pink and white Betty Wormald - Bright pink. Large flowers.
AZALEAS - Species Mars - Nearly leaf hardy.
albrechtii - Deep pink Excellent red flowers.
arborescens - White, fragrant Naomi - Leaf hardy. Hasn't set flower buds.
atlanticum - White to pink, Dwarf. David Gable - Winter killed.
Pink Twins - Winter killed.
bakeri - Orange red to scarlet Purple Splendour - Purple flowers, darker blotch.
calendulaceum - Yellow to orange. NEW HYBRIDS, Not Yet Tried Sufficiently
Flowers with the leaves. Dexter hybrids:
canadense - Rose-purple. Brookville
japonicum - Salmon pink to yellow white Wissahickon
kaempferi - Brick red Scintillation - has flowered at Delmar,
nudiflorum - Pale pink to almond white but flowers lost each year.
roseum - Pale pink to rose pink. Fragrant. Wheatley
schlippenbachii - Pink, white Westbury
vaseyi - Pale pink to white Leach hybrids:
viscosum - White. Fragrant. Native. Janet Blair
AZALEA HYBRIDS - Ghent Shammarello hybrids:
Coccinea Speciosa - Orange-red Holden
Daviesi - Yellow white. Fragrant. Tony

Almost all Kurume azaleas and the large-flowered double azaleas offered by the florists as forced plants at Christmas and Easter are all tender in our area.