azaleas are underutilized in the typical home landscape. Native
plants add the benefit of attracting pollinators to the garden.
Many contribute fragrance and fall color to the garden. To
maximize the performance of these plants, they should be grown
in acidic, organically-rich, moist, well-drained soil and
exposed to several hours of sun daily.
The following is a
selection of Pennsylvania natives and cultivars. All are
deciduous and start to bloom in late-spring or early-summer:
▪ Rhododendron arborescens (sweet azalea) – This azalea is a
large, loosely branched shrub that grows 8 – 12 feet tall with
an equal spread. Fragrant, white or pink-tinged flowers, with
red stamens form in the summer. The glossy, bright green leaves
change to deep-red and purple in the fall.
▪ Rhododendron calendulaceum (flame azalea)
– Grows 4 –10 feet tall and wide. In early summer, showy,
yellow, orange or red are formed. The medium-green
foliage changes to yellow and red before the leaves drop.
▪ Rhododendron c. ‘Wahsega’ (‘Wahsega’ flame
azalea) – This cultivar is similar in size and habit to the
species. The flowers of the azalea have a deep red coloration.
▪ Rhododendron viscosum (swamp azalea) –
This native azalea has a loose, open habit, reaching 5 – 6 feet
tall and wide. In mid-summer, clusters of white, clove-scented
flowers are formed. Fall color is orange to maroon. This
species tolerates wet soils.
▪ Rhododendron v. ‘Betty Cummins’ (‘Betty
Cummins’ swamp azalea) – This cultivar is similar in habit
to the species, except with deep pink flowers.
▪ Rhododendron v. ‘Delaware Blue’ (‘Delaware
Blue’ swamp azalea) – Another cultivar that grows to 5 feet
tall and wide and blooms in summer. The flowers are lightly
scented and have a pink shell, white overtones and pink
throats. The deep-green foliage turns to an outstanding yellow
in the fall.
▪ Rhododendron v. ‘Pink Mist’ (‘Pink Mist’
swamp azalea) – This cultivar is also similar in habit to
the species. The flowers form in summer and are white, with a
The quest by plant breeders to develop shrubs
with extended blooming periods has resulted in the introduction
of re-blooming azaleas. These azaleas are evergreen, available
in a variety of colors, and bloom in the spring, summer and
fall. The cultural requirements are the same as for any azalea
– grow in acidic, organically-rich, moist, well-drained soil and
exposure to several hours of sun daily. The current groups of
re-blooming azaleas are known as Encore® and Bloom-A-Thon®
▪ Encore® azaleas were introduced by a
breeder in Alabama and have been in the marketplace for over 15
years. They are available in 29 varieties of colors and sizes.
They are recommended for hardiness zones 7 to 10; however,
cold-hardiness trials suggest that some of the azalea varieties
are suitable for zones 6b (-5 to 0 degrees F) and 6a (-10 to -5
degrees F). According to the 2012 USDA Plant Hardiness Zone
Map, all of Allegheny County is zone 6a or 6b. Therefore, the
trial-tested 6a and 6b azaleas should grow in our area.
However, initial reports indicate that the performance of the
6a/6b azaleas is questionable for Allegheny County. This may be
due in part to the fact that they are grown in Alabama!
▪ Bloom-A-Thon® azaleas were developed by
Bob and Lisa Head in Seneca, South Carolina. The azaleas were
introduced in 2012 and are available in four colors – red,
double pink, lavender, white. Their hardiness rating is zones 6
to 9. No reports were found to determine the hardiness of these
azaleas in our area.
Despite the caveat of the southern heritage of
these azaleas, adventurous gardeners may want to experiment with
re-blooming azaleas to determine whether they are truly hardy in
zones 6a and 6b. For my part, I plan to trial several of the
re-blooming azaleas, starting late spring. If all of our
efforts are successful, these beautiful shrubs will add another
dimension to the garden.
▪ Azaleas are in the rhododendron genus.
▪ All azaleas are rhododendrons; not all
rhododendrons are azaleas.
▪ Rhododendrons are mainly evergreen; many
azaleas are deciduous.
▪ Rhododendrons tend to have bell-shaped flowers;
azalea flowers are funnel-shaped.
▪ Rhododendrons have 10 or more stamens per
flower; azaleas usually have 5 stamens per flower. [Note: A
stamen is the male part of the flower that juts out from the
▪ The optimal soil pH range for growing
rhododendrons is 5.0 to 6.0. Contact a local nursery or Penn
State Extension for a soil test kit.