Rhododendron
Rhododendron species (ERICACEAE)
Planting and Growing Rhododendron
You’ll find everything you need to know to plant and grow rhododendron in the accompanying table’s tabs:
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- Flowers, foliage, and woody fruit of rhododendron
- Growing conditions for rhododendron
- When and where to plant rhododendron
- How to plant rhododendron
- How to shape, prune and control growth of rhododendron
- Watering, fertilizing, and care of rhododendron
- Landscape uses of rhododendron
- Pest and disease control for rhododendron
Growing Rhododendron
More than 15 species and over 500 varied hybrid cultivars of slow-growing, spreading, woody, mostly evergreen shrubs or small trees, to 25 ft. (7.5 m) tall and wide, with waxy, deep green, oval to lance-shaped leaves, to 1 ft. (30 cm) long, in radiating clusters.
Dwarf forms and tree-habit cultivars available.
Rhododendron Planting and Care Guide
Flowers and Fruit
Very showy, lightly fragrant, trumpet-shaped, cream, lavender, orange, pink, purple, red, white, yellow flowers, to 8 in. (20 cm) long, in spring–summer, in pom pom-like trusses or clusters, to 16 in. (40 cm) wide, at the ends of branches, form woody, capsulelike fruit in summer.
Best Climates
U.S.D.A. Plant Hardiness Zones 6–10. Hardy or semi-hardy, depending on cultivar.
Soil Type and Fertility
Moist, well-drained soil. Fertility: Rich. 5.5–6.5 pH. Best in mild climates.
Where and How to Plant
Filtered sun to partial shade. Space 6–10 ft. (1.8–3 m) apart.
Proper Care
Moderate. Keep moist until established; reduce watering thereafter. Fertilize monthly spring–autumn. Avoid cultivating around plants. Deadhead spent flowers to prevent seed pods from forming, cutting their stems 1/2-in. (12-mm) above emerging new growth. Propagate by cuttings, layering. Protect from sun in hot climates.
Shaping and Pruning
Rhododendrons flower on their prior-year growth. Shape-prune plants only after bloom as pruning in other seasons removes flower buds.
To shape rhododendrons, remove only a single rosette of leaves and the internode stem below, cutting 1/4-in. (6-mm) above the lower rosette. Pinch tips of early new end-of-branch growth in spring to increase flowering.
Rejuvenate older plants in winter while dormant. Leave at least 18 in. (45 cm) of wood on every branch after making cuts.
For natural appearance after regrowth, make cuts randomly at a different heights and vary the after-pruning length of the branches about a third to a half long around the plant.
Latent buds in the remaining wood will grow to produce new branches. After branches form from these buds, remove any that cross through the shrub’s center or appear irregular.
About This Species
Good choice for accents, backgrounds, borders, containers, fencelines, screens in small-space, woodland gardens. Disease resistant. Root weevil susceptible.
Species Rhododendrons:
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- Rhododendron brachycarpum, Fujiyama rhododendron
- Rhododendron dauricum, Dahurian rhododendron
- Rhododendron degronianum subsp. yakushimanum, Yak rhododendron
- Rhododendron falconeri, Falconer rhododendron
- Rhododendron fortunei, Fortune’s rhododendron
- Rhododendron forrestii subsp. forestii, Forrest rhododendron
- Rhododendron keiskei, Keiskei rhododendron
- Rhododendron macrophyllum, Pacific rhododendron
- Rhododendron metternichii, Metternich rhododendron
- Rhododendron mucronulatum, Korean rhododendron
- Rhododendron pemakoense, Burma rhododendron
- Rhododendron racemosum, racemose rhododendron
- Rhododendron rupicola var. chryseum, Corydalis rhododendron
- Rhododendron smirnowii, Smirnow rhododendron
Hybrid Evergreen Azaleas:
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- Belgian Indian hybrids
- Belgian–Glen Dale hybrids
- Greenwood hybrids
- Kaempferi hybrids
- Kehr hybrids
- Kurume hybrids
- Linwood hybrids
- Macrantha hybrids
- North Tisbury hybrids
- Satsuki hybrids
- Southern Indian hybrids
Hybrid Deciduous Azaleas:
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- Ghent hybrids
- Mollis hybrids
- Occidentale hybrids
- Vicosum hybrids
About Azalea and Rhododendron
Azaleas and rhododendrons comprise the nearly 800 varied species and many thousands of named cultivars of bushy, broad-leaved, evergreen and deciduous shrubs and small trees of the Rhodendron genus.
Azaleas and rhododendrons are prized for their large, showy, clustered flowers in shades of cream, orange, pink, red, white, or yellow, which appear in spring or summer. Both types of rhododendron are native to the temperate zone of the northern hemisphere, most commonly to mountainous Asia.
While azaleas and rhododendrons are mostly hardy or semi-hardy, and well-suited to climates as cold as U.S.D.A. Plant Hardiness Zone 4, note their other climate, soil, and site requirements. These factors limit their growth in many regions of central North America.
Slow-growing shrubs, azaleas are mostly under 10 ft. (3 m) tall. Rhododendrons, by contrast, may reach 25 ft. (7.5 m) in height.
They’re good container as well as landscape plants, seldom need pruning, and are best in filtered sun and partial or full shade.
Most hydrangeas are susceptible to aphids and mildew when conditions are too cool and moist. Prune them once their flowers fade in autumn, or in spring before growth begins.
Choose from among the most popular species of Azalea and Rhododendron, listed above.
Planting and Caring for Azalea and Rhododendron
In general, azaleas frequently bloom ahead of the rhododendrons, have hairy undersides on their leaves, and bear flower clusters that are a bit smaller than their larger cousins. Garden centers offer many new cultivars of hybrid azaleas each spring.
There are technical horticultural differences between azaleas and rhododendrons. The Azalea Society of America and the American Rhododendron Society have divided them into respective show classes based on these differences.
Members of the Rhododendron genus are outstanding plants for shady gardens. They perform remarkably in moist climates such as in New England, the Mid-Atlantic, the Great Lakes, the Pacific Northwest, and the South regions of the United States and in British Columbia and the Maritime Provinces of Canada.
Plant azaleas and rhododendrons in moist, well-drained, acidic soil rich in organic humus. They do best in sites with filtered sun or partial shade. Give them regular feedings with an acidic fertilizer, and watch them prosper.
The landscape location ideal for both types of rhododendron is the understory of deciduous or conifer trees borders and islands. Azaleas are good container plants for small-space gardens, decks, and patios, and they can be moved indoors as short-term houseplants during their bloom.
Azaleas and rhododendrons are divas of the landscape garden that can shine in any woodland meadow.