Azaleas vs. Rhododendrons: What’s The Difference?
Are you trying to figure out the difference between an azalea and a rhododendron? These two shrubs can confuse even the most experienced gardeners. In this article, gardening expert Jill Drago looks at the differences between these two flowering shrubs, as well as thier similarities.
Azaleas and rhododendrons are beautiful flowering shrubs that grace our gardens with their flowers in the spring and early summer. They are known to be some of the hardiest perennial shrubs that can be grown in warmer climates.
Both azaleas and rhododendrons bloom in a variety of colors, including pink, purple, white, red, yellow, and orange. Most varieties thrive in full to partial shade. They also have comparable temperature and climate needs.
With so many similarities between the two, where are they different? Maybe you would just like a few tips to help you identify these blooming shrubs! Let’s find out the difference between rhododendrons and azaleas, and how to care for both.
The Short Answer
This is a tricky one to sort out. All azaleas are rhododendrons, but not all rhododendrons are azaleas. This was best said by the American Rhododendron Society. There are more similarities than there are differences between azaleas and rhododendrons. They both bloom brightly in the spring, have lush foliage, and require the same growing conditions. Let’s break it down a bit further.
The Long Answer
There are so many similarities between rhododendrons and azaleas, especially how they look, it can be confusing to tell the two apart. Let’s break down in detail the differences that set these two apart from one another.
Azaleas and rhododendrons are so closely related they share the same genus, Rhododendron. Azaleas are a subspecies of the genus Rhododendron. Botanists believe that there are too few botanical differences between the two shrubs to make azalea its own genus.
Both azaleas and rhododendrons are members of the Ericaceae family. This plant family is made up mostly of shrubs and small trees. The plants are always acid-loving, and largely evergreen. Other plants from this family are blueberries, heath, and heather.
You can find azaleas and rhododendrons growing naturally in many parts of the world. However, the species that have been cultivated and become popular in our gardens are native to areas in Asia as well as the southeastern United States.
Flower Size and Shape
Rhododendron flowers are bell-shaped, whereas azalea flowers are trumpet-shaped.
Azalea flowers could be single, or double and any variation of petal quantity in between. Rhododendron flowers are clustered into groups of flowers called trusses. These trusses could hold anywhere from 5-20 flowers depending on the variety.
As far as the size of each flower goes, it will vary greatly depending on species and variety.
Other Flower Characteristics
Each flower on a rhododendron or an azalea has stamens. The difference here is the number of stamens. Azaleas have five stamens. Rhododendrons have 10 stamens.
Both azalea and rhododendron flowers can be one solid color, or they can have some freckling and splotches on their petals.
Leaf Characteristics and Size
Throughout all of the varieties of azaleas and rhododendrons, you will find the majority of these shrubs are evergreen. There are azaleas that are deciduous, but there are also evergreen and semi-evergreen azaleas.
Between azaleas and rhododendrons, there is another classification: elepidote vs. lepidote. Lepidote leaves have tiny scales on them and are usually smaller leaves.
Elepidote leaves have larger leaves and do not have any scales on the leaves. Azaleas have smaller leaves, however, they are elepidote and tend to have tiny hairs on their leaves.
Both azaleas and rhododendrons have varieties that produce beautiful fall colors. These colors range from bronze to deep red and purple.
Size and Growth Rate
While there is always an exception to the rule, rhododendrons will grow taller and wider than most azaleas. On average azaleas will grow to about 4-6 feet tall, and rhododendrons will grow to be around 8-12 feet. There are of course taller varieties of each.
Rhododendrons never really stop growing, these measurements are a projected average for a 10-year-old shrub.
There are several dwarf varieties of azalea that are available at most garden centers and nurseries. These dwarf varieties only grow about 1-3 feet tall. They are excellent for small spaces or container gardens.
Azaleas and rhododendrons grow moderately and will produce less than one foot per year.
Both rhododendrons and azaleas are classified as perennial evergreen shrubs. This means that their leaves stay green all year around and they bloom every spring through summer. With the right care, these shrubs should thrive in most environments.
Azaleas have been hybridized to be tolerant of many different growing situations. They are a bit more tolerant of heat and sun than rhododendrons in general.
However, both azaleas and rhododendrons do best in partial shade. Too much shade and they won’t produce flower buds. Too much sun and the leaves and flowers will get scorched.
Planting your azaleas and rhododendrons under deciduous trees will provide the right amount of shade to your shrubs.
Acid soil has a pH of anywhere from 4.6-6, which is pretty acidic. If you are unsure what the soil pH is in your area, I would recommend getting a soil test, or a pH test, done.
Rhododendrons and azaleas will let you know if they are not growing in acidic soil. You may notice yellow leaves.
If you need to lower your pH to create a happier home for your rhododendrons you can add wettable sulfur which you can find at your local garden center. Be sure to do a soil test before adding anything to your soil!
Both azaleas and rhododendrons are shallow-rooted plants. Unlike other shrubs that have a long taproot, azaleas and rhododendrons have fibrous root systems which typically will only be one or two feet deep.
Because of this type of root system, your azaleas and rhododendrons may dry out quickly if they are planted in direct sun or if you are experiencing a hot stretch of weather.
Ensure your plants are getting about one inch of water a week. Use mulch around the base of the plant to help maintain moisture in the soil.
Too much water in the soil can be an issue for rhododendrons and azaleas. These shrubs are prone to root rot if they are sitting in too much water for too long. Aim for moist, well-draining soil and your shrubs will be in good shape.
If you have nice fertile soil for your azaleas and o to grow in, you may not need to add any additional fertilizer.
Adding compost to your gardens is a great way to boost soil fertility, especially if you are unsure of the content of the soil.
If you would like to add a granular fertilizer to your established azaleas or rhododendrons be sure to do so before July. Adding fertilizer after that point will promote vegetative growth when the shrubs should shift their energy into producing flower buds.
Both azaleas and rhododendrons are prone to issues with fungal diseases. These diseases could be powdery mildew, petal blight, gall, or rust.
The good news about these diseases is that they are preventable and treatable for the most part. The best way to prevent these diseases from taking hold is to keep your garden clear of debris such as leaf litter. Leaf litter could be carrying fungal spores that are just waiting to splash up on your healthy leaves.
If you need to treat your diseased azaleas and rhododendrons look for a copper fungicide at your local garden center. Read the label thoroughly to ensure you apply at the correct time and at the appropriate rate.
Azaleas and rhododendrons both deal with your average garden pests such as aphids, spider mites, and scale.
Azaleas however seem to be a bit more at risk for leaf miners, lace bugs, and whiteflies. These insects focus on eating and damaging the leaves of the rhododendron.
Using a broad-spectrum insecticide will help to control these insects. You can also use horticultural oil to control these insects as well as many other bugs you may find in your yard.
Even though both azaleas and rhododendrons can get quite large, they are actually very versatile shrubs in your landscape.
Dwarf rhododendrons and azaleas are great choices for large containers and for border gardens. The larger varieties can be used in mass plantings, creating swaths of bright color in shady areas.
Rhododendrons, and their evergreen leaves, are wonderful for privacy screens that will last and provide coverage throughout the winter months.
|Asia, S.E. United States
|Asia, S.E. United States
|¼ inch- 5 inch
|Spring- Summer, and Fall
|Acidic, well draining
|Acidic, well draining
|Caterpillars, Lace Bugs, Leaf Miners, Nematodes, Scale, White Flies
|Black Vine Weevil, Lace Bugs, Spider Mites
|Container, Hedge, Mass Planting
|Container, Hedge, Mass Planting, Privacy Screen
If you are unsure whether you have an azalea or a rhododendron growing in your yard, hopefully, the above characteristics will help you identify your plant. Until you know for sure, keep your shrubs watered, and only prune as needed.