Rhododendrons are wildly popular due to the spectacular beauty of their clusters of brightly-colored blossoms. With blossoms available in shades of pink and purple, red and white, explode during the spring and summer months. During winter, many varieties have large green leaves year-round, and some of them grow fast.
The growth rate of rhododendrons varies greatly depending on the type. For example, some varieties grow at an annual rate of less than an inch, while others grow as fast as two feet per year. Additionally, blossoming occurs much slower in plants grown from seeds than from cuttings.
The rest of this article will discuss the possible range of growth rates of rhododendrons, their size, and types, and how to grow them.
Growth Rates of Rhododendrons
The growth rate of rhododendrons varies greatly depending on the type. Some varieties enjoy a fast growth rate of about 2 feet (0.6 meters) per year. Other varieties of rhododendrons grow at an annual rate of about 0.5 inches (1 centimeter).
The American Rhododendron Society’s online database lists plant height estimates after ten years of growth on their website’s searchable database. Their list includes 44 hybrids (cultivars) that grow 1 foot in ten years, 164 that grow 2 feet, 366 that grow 3 feet, 281 that grow 4 feet, 288 that grow 5 feet, and so forth.
Most home gardeners purchase rhododendron plants in full bloom online or from a garden store. Although rhododendron seeds are available, most gardeners don’t grow them from seed as it typically takes about 2 to 10 years for their first blossoms to appear.
Cultivating a rhododendron from a cutting is possible. However, that method also requires patience as growing roots can take as long as three to four months.
Sizes of Rhododendrons
Rhododendrons are capable of growing indefinitely. As a result, they have there is no limit to how tall they can grow. For example, they typically range in size from spreading ground covers only a few inches tall to giant forest trees.
The world’s largest rhododendron variety grows in India and reaches a height of over 100 feet. However, the majority of rhododendrons range from three to six feet in height.
Botanists and horticulturists group rhododendrons into two categories based on whether they are evergreen or deciduous (shed their foliage during winter). Additionally, they are frequently categorized based on whether or not they have scales on the lower leaf surface.
Popular rhododendron types include:
- April Rose: These shrubs require full sun to partial shade, medium moisture, and soil that is moist and well-draining. Cold-hardy plants that can withstand temperatures as low as -25ºF (-31.7ºC), they are popular for their 2-inch wide, purple, funnel-like blossoms. Mature plants are 3 to 4 feet tall (0.9 to 1.2 meters).
- Golden Lights: These plants require full sun to partial shade, medium moisture, and well-draining soil. Extremely cold-hardy plants that can withstand temperatures as low as -35ºF (-37.2ºC), their blossoms begin as red-orange colored buds that open in early summer revealing funnel-shaped orange flowers with ruffled edges. Mature plants grow to about 6 feet (1.8 meters).
- Nova Zembla: Nova Zembla requires partial sun, medium moisture, and well-draining soil. These plants are low-maintenance and grow vibrant red blossoms beginning in the middle of spring. Prolific bloomers, mature plants are about 8 feet (2.4 meters) tall.
- Rhododendron Rubiginosum: These shrubs require partial shade, medium moisture, and well-draining soil. These evergreen shrubs bloom beginning in spring, and their trumpet-shaped flowers range from pale pink to pale lavender. Additionally, their blossoms are freckled with dark red or purple spots. Mature plants grow to about 20 feet (6.1 meters) tall.
- Saffron Queen: This variety requires full sun to partial shade, medium moisture, and well-draining moist soil. Only suitable for temperate climates (minimum temperatures of 20 ºF), Saffron Queens grow bright yellow colored trumpet-shaped flowers. Mature plants are about 6 feet (1.8 meters) tall.
- Windbeam: Windbeams require full sun to partial shade, medium moisture, and well-draining moist soil. These shrubs bloom abundantly in the middle of spring. Eight flowers form its sphere-shaped flowers, and the blossoms start white and gently fade to pale pink. Mature plants are about 4 feet (1.2 meters) tall.
Growing and tending rhododendrons is relatively simple. However, growing them does require proper planting location, soil preparation, and planting practices.
The Best Location for Planting Rhododendrons
Most rhododendrons grow best in reasonably mild, humid climates. It is best to plant them in a location providing shelter from the wind. For example, buildings, fences, and slopes serve as suitable barriers.
Likewise, planting evergreen trees and shrubs like juniper, pine, and spruce to the south or west of rhododendrons helps protect them. And, they provide an excellent backdrop when they are blooming.
Preparing the Substrate for Rhododendrons
Rhododendrons require soil that is carefully prepared. Gardeners need to consider the following items carefully:
- Drainage: Proper drainage is essential since the roots of rhododendrons are delicate. For that reason, a site that slopes to the north or east is usually best because it protects them from drying winds from the south and west.
- Soil acidity: Rhododendrons require acidic soil. Most of these plants grow best at a soil pH between 4.5 and 6.0. Soils previously limed for a lawn or garden may need to have the pH lowered. Soil pH test strips are available online, or you can take a soil sample to your local extension service.
- Correcting the pH: If the pH level is too high, it can be made more acidic by applying iron sulfate or agricultural sulfur. If the soil is too acidic (below a pH of 4.5), using ground limestone will raise it.
- Mixing the soil: Rhododendrons require large amounts of organic matter for proper growth. A mixture of 50 percent pine bark, 25 percent topsoil, and 25 percent compost works best.
The best time to plant rhododendrons is in the autumn when their roots have time to acclimate and get ready for spring.
- Setting the plants: Most rhododendrons are purchased with soil “balled and burlapped” or in containers. Dig a hole in the flowerbed that is slightly larger than the container or ball, but no deeper. Next, set the plant, so the ball of roots is about two inches higher than the surrounding soil. Then, firm the soil around the plant and soak it thoroughly with water.
- Fertilizer: Rhododendrons don’t require fertilizer at the time of planting. However, a light application of fertilizer formulated for rhododendrons or azaleas can be added to the soil before adding mulch.
- Mulch: Most rhododendrons require heavy mulch to help them conserve moisture. Course materials like hardwood chips or sphagnum peat moss are ideal. Spread the chips or peat moss four to six inches deep around the base of the plant.
Rhododendrons are among the most popular garden shrubs with their spectacular explosion of spring flowers. Additionally, they are plants for all seasons with rich deep-green leaves that add pleasing color to the garden during autumn and winter.
Best of all, growing a spectacular garden filled with rhododendrons is simple and doesn’t cost a lot of money.
If you are a gardener, you might consider bookmarking this article for future reference.
And until we meet again, the best of luck with that green thumb!