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The Difference Between Rhododendrons and Azaleas

The Difference Between Rhododendrons and Azaleas

By Natalie Carmolli, Proven Winners® ColorChoice®
Photographs courtesy of Proven Winners® ColorChoice®

Deciphering the difference between a rhododendron and an azalea can be complicated at first glance. But there are a couple of easily observable differences that will make you look like a rhodie expert in any garden.

To begin, one thing that is always true is that you can refer to any these fantastically floral shrubs as rhododendrons. But here’s where it gets tricky…conversely, you cannot always call rhododendrons, azaleas. Confused yet? Let’s break it down.

Just as “lilac” is the common name for the genus, Syringa, “azalea” is a common name for the genus Rhododendron. However, unlike with lilacs, the label rhododendron is also used as a common name.

So it follows that all azaleas are Rhododendrons, but it is not the case that all rhododendrons are azaleas. So how do you tell them apart?

Here is a simple differentiator – azaleas have funnel-shaped flowers that open a little wider and more flat, while Rhododendron flowers are bell-shaped.

Also, the New York Chapter of the American Rhododendron Society tells us that, "True rhododendrons have 10 or more stamens which is 2 per lobe. Azaleas usually have 5 stamens or 1 per lobe. Azaleas have 5 lobes in a flower.”

(If you need a refresher on flower anatomy, the American Museum of Natural History provides this very good illustration.)

Let’s take a look at the differences in blooms using a couple of popular cultivars:

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Rhododendron Dandy Man Color Wheel® (top) and Dandy Man® Pink (bottom) both have the distinct, bell-shaped flowers with 10 or more stamens, and the waxy, leathery foliage of true rhododendrons.

This cultivar is bred to be very hardy, surviving down to zone 5, plus, the cross with the R. hyperythrum species also makes it more heat tolerant, up to zone 9. Dandy Man® Purple Rhododendron is even more cold hardy, down to zone 4.

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The Bloom-A Thon® series of azaleas (pictured) share the funnel-shaped flowers that have a flatter, more open, presentation with fewer stamens than the Dandy Man® rhododendrons. You’ll also find the foliage to be softer, and is semi-evergreen in the cooler end of its hardiness zone. This series does like to be planted in a little warmer climate, in USDA zones 7-9, but it produces continuous cycles of blooms throughout the heat of the summer, all the way through fall.

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Looking for more ways to tell azaleas and rhododendrons apart? The New York Chapter of the American Rhododendron Society further explains that, “Azaleas tend to have appressed hairs, which is hair parallel to the surface of the leaf. This is particularly true along the midrib on the underside of the leaf. It is easily seen in "evergreen" azaleas. True rhododendrons instead of hair are often scaly or have small dots on the underside of the leaf. Azalea leaves are never dotted with scales and are frequently pubescent."

One final note, both azaleas and rhododendrons are toxic. So keep these shrubs away from places where livestock might try to feed on them and exercise caution in gardens that also host epicurious pets and small children.

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Photos and story by Monrovia Nursery Company

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