DECIDOUS AZALEAS & RHODODENDRONS
Rhododendrons and Azaleas have long been the go-to plant for northwest gardens. They love it here, so it’s an easy choice. There is a large group of them however that has been overlooked for years; the ones that lose their leaves in winter. Dramatic flower color and sweet perfume, lovely fall leaves and self-sufficiency are some of their best qualities. Plus they thrive in sunshine while their evergreen relatives burn.
Many of the plants listed below were bred from Azaleas that are native to the United States. Knapp Hill Nursery, Goldsworth Old Nursery and Exbury began to hybridize in the late 1800s using R. calendulaceum and R. arborescens (both native to eastern U.S.), R. occidentale (native to the Pacific Northwest), and R. molle (native to China). Many of their hybrids are still sold today. Locally Ivan and Robertha Arneson used those hybrids to breed new Azaleas into the 1990’s. Arneson Azlaeas are now some of the best and most popular on the market.
The Difference between Azaleas and Rhododendrons
- All Azaleas are members of the genus Rhododendron.
- Deciduous Azaleas are in the subgenus Pentanthera,
- Evergreen Azaleas are in the subgenus Tsustusti.
- All Azaleas are elepidotes; they never have scales on the bottom side of their leaves.
- Azaleas have 5 lobes on the flower.
- Azaleas have hairs on their leaves that grow parallel to the leaf surface.
The Crystal Springs Rhododendron Garden near Reed College is a wonderful place to see deciduous rhododendrons in bloom in spring.
Some of our favorite Azaleas:
Azalea ‘Arneson Flame’ – Bright red flowers, fuzzy red-tinged new leaves turn green in summer and maroon in autumn. Grows 3’ x 4’.
Azalea ‘Arneson Gem’ – Red flower buds open to yellow-orange flowers w/ red edges, disease resistant leaves, maroon color in autumn. Grows to 3’ x 4’.
Azalea ‘Arneson Ruby Princess’ – Dark red flowers, new leaves tinged red turn green in summer and maroon in autumn. Dense rather than open growth. 3’ x 4’.
Azaela ‘Cannon’s Double’ – Cream, gold and pink double(many petals) flowers. New leaves have a bronze cast & turn green in summer. Upright, open & airy growth to 5’ x 6’.
Azalea ‘Fragrant Star’ – Slender & elegant white flowers with intense sweet fragrance and frosty blue-green leaves that turn orange and red in fall. Grows to 4’ x 4’.
Azalea ‘Gibraltar’ – Red flower buds, deep orange flowers w/ gold tinge on the upper lobe. Leaves are mildew resistant. Grows to 4’ x 4’.
Azalea ‘Homebush’ – Bubblegum pink double flowers with pointed petals in a tight ball-like cluster. Grows in an upright open shape to 6’ x 5’.
Azalea ‘Klondyke’ – Orange flower buds open to gold flowers. New leaves are tinged with bronze and turn green in summer. Grows to 4-6’ tall, 3-5’ wide.
Azalea ‘Mandarin Lights’ – Red-orange flower buds open to only slightly lighter orange flowers. Grows to 5’ x 4’. The ‘Lights’ series is more cold tolerant than other Deciduous Azaleas, hardy to Zone 4, or -30 to -40f.
Azalea ‘Mary Poppins’ – Orange flowers with hints of gold and apricot have petals with frilled edges, much like the border of a fancy parasol. Grows to 4’ x 4’.
Azaela ‘Northern Hi-Lights’ – White flowers with a strong yellow blotch on the upper petal. Blooms open along with the appearance of new leaves, a bit later than others. Grows to 4’ x 3-4’, Hardy to Z4, -40f.
Azalea ‘Red Sunset’ – Excellent true-red flowers with frilled edges and dark green leaves. Compact growth to 3’ x 3’.
Florida Azalea R. austrinum, native to Florida, Georgia, Alabama & Mississippi – Flower color varies on plants in the wild that grow from seedlings. Clear yellow, cream orange to red flowers are fragrant and open in April-May. Cultivated varieties are propagated from cuttings, so flower color is more predictable. Green leaves. Grows to 8-10’ tall in an upright open shape. Hardy Z7, 0-10f.
Western Azalea R. occidentale, native to Oregon and California coastal areas – Flower color varies on plants found in the wild, or in plants grown from seeds. White, pale pink, yellow to orange or combinations of all of these colors are common. Flowers have a sweet honeysuckle-like scent and bloom in mid April to early May. Leaves are green and turn yellow, orange and red in fall. Growth is more compact than many other deciduous Azaleas, to about 3-5’ with a more dense shape. Hardy to -5f.
Sweet Azalea R. luteum, native to eastern Europe & southwest Asia – Rich yellow scented flowers are tubular with very sticky outsides in early May. Green leaves, vigorous grower to 8-10’ given time. Hardy Z5.
Korean Rhododendron R. mucronulatum, native to N.China, N.Japan, Korea, Manchuria & Mongolia - The first rhododendron to bloom in late winter-spring, just after witch hazels. Flowers are mauve pink, but several cultivars with differing flower colors are available, the most popular being ‘Cornell Pink’, with bubblegum pink flowers. In SE Portland there are some R. mucronulatum prominently set at the edge of Laurehurst Park along Caeser Chavez Blvd. that always draw a lot of attention when in bloom. Leaves are green and plants grow to 4-8’ tall and wide with an open upright shape. Hardy Z4.
Royal Azalea R. schlippenbachii, native to Korea, Manchuria & eastern Russia – Pink fragrant flowers appear before or with the leaves. The cultivar ‘Sid’s Royal Pink’ is commonly available and has even pinker flowers. New leaves are tinged purple, turn green in summer and have excellent orange, yellow & red in autumn. This is a good choice for growing east of the Cascades because it adapts to alkaline soil, accepting pH of up to 7. Grows to 6-8’ tall, Hardy Z4.
FACTS: DECIDUOUS RHODODENDRON
Common: Deciduous, Exbury, Mollis, Western, Sweet, Coast Azalea
Origin: Eastern & Western North America, Asia & Europe
Characteristics: All Rhododendrons & Azaleas included in this article lose their leaves during winter. Flowers can be white, pink, yellow, orange, red or a combination of several colors. Most are sweetly fragrant. Some flowers are tube-shape, others are funnel-shape and some are double, having extra petals.
Bloom is from late winter to mid spring.
Leaves open with the arrival of flowers or just following bloom. Most are green but some are frosty blue-green and both types display excellent orange, red & purple color before falling in autumn. Some display bronze or red-tinged new leaf growth.
Size: Most grow to around 4-5 feet tall x 5-6’ wide, but can get larger given time.
Culture: Unlike their evergreen relatives, Deciduous Azaleas and Rhododendrons thrive in full sun. Part-shade to shade is fine too. Plants grown in more shade will have an open airy shape and fewer flowers than plants grown with more light.
Any Rhododendron or Azalea prefers well-drained soil with an acidic pH. The Pacific Northwest naturally has soil with low pH because of the copious rain, but much of the area has heavy clay soil, so mixing compost to the bed before planting is advised. Rhodies and Azaleas have shallow root systems and prefer not to be heavily mulched.
Any fertilizer used should be specific to acid-loving plants, and directions should be followed carefully.
Problems: Enemy number one is powdery mildew. Most Deciduous Azaleas and Rhododendrons are subject to powdery mildew on the leaves during the warmth of summer.
Options for combating this enemy are many and include:
- Chemical warfare. Synthetic and organic options are available and must be used often and without sympathy.
- Water leaves in the morning. The idea is that the spores that make Powdery Mildew can be washed off. If the leaves are wet during the night mildew spreads, so allow plenty of time for leaves to dry before nightfall. This is not a fool-proof method, especially considering that rain cannot be controlled, but for those who prefer not to spray, it may be worth a try.
- Passive acceptance. Powdery Mildew will not (usually) kill the plant.
For more information on disease problems and solutions, follow this link to the OSU website: