A Rhododendron bush is a popular flowering bush and foundation plant, with bright spring blooms. They are native to tropical and temperate regions. While it is a bush, Rhododendron bushes can grow up to 80 feet tall!
Rhododendron plants are closely related to Azaleas. The biggest difference between the Rhododendron plant and an Azalea bush and a Rhododendron is an evergreen bush. (Note: There are a few varieties of deciduous Rhododendrons, but they are not too popular with homeowners) Generally speaking, Rhododendron plants are larger in height, leaves, and blooms compared to Azaleas. The Rhododendron also has a leathery type of leaf.
Flowers Bloom: Mid-Spring.
Flower Colors: Varying shades of orange, pink, purple, red, white, and yellow. Also, there are multi-colored blooms.
Plant height: up to 80 feet tall.
Plant Hardiness Zones: 3 – 9
Rhododendrons are grown from seeds, cuttings, or grafting. Most home gardeners do not start Rhododendrons from seed, as a plant grown from seed takes 2-10 years to produce the first bloom. Most homeowners buy established Rhododendron plants while in full bloom from a garden store. Then, transplant the Rhododendron bush outdoors, after the blooms have died off.
Planting and transplanting Rhododendrons is best done in the early spring or early fall. When transplanting, replant bushes at the same level in the ground as they were in their original location. Smaller bushes transplant best.
Rhododendrons are acid-loving plants. They grow best in light shade and need protection from the midday sun and winter sun. They prefer moist, well-drained soil with a pH of 5.5. Check the soil pH before planting, especially if planting along a foundation where soils tend to be more alkaline. Adjust the pH, as needed. Mix in plenty of inorganic matter, and well-rotted manure.
The selection of a location is important. Rhododendrons can be harmed or killed by sustained winds and by too much direct sunlight. Select a location out of the direct sunlight if possible. Protection from the strong midday sun and winter sunlight are important. Otherwise, the leaves dry out and/or burn. Select a planting site with a northern exposure. It is also important to provide protection from winds. A low-lying area or one protected by a building or a hedgerow is a good choice.
Rhododendrons prefer moist soil. It is important to water the plants during extended dry spells, even in the fall.
Using pine needles (acidic pH) as mulch works to help keep the soil moist, and maintain/add acidity to the soil. Roots are shallow, so mulching will help to keep the weeds down, without disturbing the root system.
Ideal Soil pH: 4.5 – 6.0.
Pinching or pruning back young plants helps to promote bushy growth. Pruning should be done early in the spring. But any pruning may result in cutting off next year’s blooms. If you prune an established bush heavily, it may not bloom again for two to three years. At the thought of losing next year’s blooms, we recommend avoiding pruning established plants at all. Just let them grow naturally however they want.
After several years, if the plant begins to grow too tall, major pruning may be needed.
Rhododendron bushes can be harmed by winter burn, resulting from frozen soil, wind, and winter sun. As previously mentioned, the selection of a location for your Rhododendrons helps to avoid wind or sun damage. Some varieties are not as tolerant to extreme cold. In northern areas of the country, ask the garden store about the cold hardiness of the variety you are buying.
You can further protect your bushes by providing windbreaks that may double to block some of the direct winter sunlight.
Insect and disease problems are infrequent. Treat with insecticides or fungicides only as needed.