Rhododendron and azalea species are found growing in the wild
from the arctic region to the tropics.
Regions suitable for growing rhododendrons and azaleas are those that have naturally acidic soils,
adequate water availability, moderate humidity and winds and lack of
temperature extremes. In the U.S. such regions
run along the east and west coasts, along the Gulf of Mexico and around the Great Lakes.
The climate of the U.S. Pacific Northwest region, especially between the Cascade Mountain
range and the Pacific Ocean, is very accommodating to the growth of many types of rhododendron hybrids and species. The
favorable climate extends down the coast to the San Francisco Bay area, which is about the southern limit for
growing the large-leaved elepidote Large leafed, large-sized plants at maturity,
that do not have scales on the underside of the leaves.varieties. Many varieties of small-leaf
lepidote Small leafed, usually low growing plants, often bloom earlier than
elepidotes, with small scales on the leaf undersides.rhododendrons also thrive in gardens along the
U.S. west coast states.
With attention to suitable hardiness, large-leaf rhododendron varieties do well in
the eastern United States, generally along the Atlantic coast from Nova Scotia to the upper Carolinas,
along both sides of the Appalachian Mountains and in southern Ontario, Michigan, Illinois, Wisconsin, Ohio,
Pennsylvania, New York, New Jersey and Connecticut.
Evergreen and deciduous azaleas do well on the west coast from British Columbia to the Mexican
border, along the Gulf Coast and throughout the southeastern U.S. and along the east coast up into the Boston
area. Some deciduous azaleas are very cold hardy and some tolerate heat and humidity. At least two
species of deciduous azaleas are native to eastern Canada and several more species are found in New England.
Many species of deciduous azaleas are native to the east, southeast and south and one species grows wild in the
west. Hybrids derived from the native species thrive over large areas of the United States.
Throughout most of the Middle West and the Great Plains rhododendrons can be grown
with special attention to growing conditions, and selecting very hardy varieties. When placing plants choose
locations that mitigate extreme temperature changes, especially in spring and fall, and provide protection from drying
summer or winter winds.
Some of the maddenii-type rhododendrons grow quite readily in southern California.
vireya rhododendrons do well in the Los Angeles basin, and can be grown outdoors in Florida,
in parts of Australia and New Zealand.
For many decades rhododendron and azalea hybridizers have been busy creating new cultivars
that have extended the range of flower color, bloom time, plant size, and hardiness,
resistance to disease, etc. This has greatly expanded the regions where rhododendrons and azaleas
can be successfully grown.
More information about rhododendron and
azalea suitability in the landscape can be found in the following Journal ARS articles:
In New England by Charles W. Findlay, Jr.
Weston Hybrids by C. J. Patterson
and Azaleas in the Middle Atlantic States by Sandra McDonald
Middle America by Donald W. Paden
Species for Pacific Northwest Woodland Gardens by Rudolph Henny
Rhododendrons in Warm Climates by Willis Harden
Evergreen Azaleas Up
From Inferiority by Franklin H. West