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Rhododendron vs. Azalea – What Are The Differences?

Most landscape gardeners are experts in planting and maintaining azaleas and rhododendrons. These shrubs are long-time favorites with both experts and amateur garden owners.

There abundant and bright flowers light-up any space and for this reason alone have a place in many cultures. In Asia, for example, countless azalea festivals celebrate the flower when they are at their most exuberant bloom.

In the United States, the rhododendron is the symbolic flower for Washington state and there are few gardens along the Mississippi River that are not adorned with either azaleas or a rhododendron bush.

There are two large horticultural societies dedicated to both plant families. Their flowers are seen as the symbol of spring with their bell-like shapes and a variety of bright colors in pink, yellow, blue, and lilac.

When studied up close the structure of the flower is fascinating but few people can tell the difference of the shrub at the hedge of their garden. The flower structure is as follows:

  • single-stemmed for the azaleas
  • in clumps of flowers for the rhododendrons

While both azaleas and rhododendrons are favorites and widely known the similarities between them make it hard for non-experts to identify between them.

In this article, we will discuss the history, differences, and symbolism between each flower in the hopes of helping the home gardener to better choose, plant, and care for their shrubbery.

History

Both names have their origin in the 18th Century in the world of the father of classification Carl Linnaeus. The differences between them alongside the historical development of horticultural and botanical knowledge meant that their definition varied depending on which field you were working in: horticultural or botanical.

Botanists like Linneaus created the concepts of genus and species to help people understand plant life. However, plants do not fit neatly into man-made boundaries. Before Linneaus time azaleas, mountain laurel, and rhododendrons where all referred to with the long name of a low-growing rose tree.

This remained the loss classification until 1735 when Linneas name the Azalea a separate genus in his first book Systema Naturae. The Azalea genus became more specific in 1753 when Linneas added 6 species to it including evergreen and deciduous azaleas.

It was in 1753 in his book Species Plantarum that he first classified the rhododendrons and into this genus, he places three flowers previously of the azalea family:

  • the piedmontes azalea
  • flame azalea
  • swamp azalea

The number of states was what he saw as the defining characteristics distinguishing azaleas from rhododendrons, with azaleas having 5 and rhododendrons having 10.

Their current classification means that all azaleas are rhododendrons not all rhododendrons are azaleas.

In reality, this classification is fairly recent and most gardeners and horticulturists have continued referring to them with their common name to avoid confusion by referring to the shared genus.

In reality, they should be two separate genera or the rhododendrons should have been subsumed into the azalea genus. More than opposites these two large groups of flowers are related to each other in their typology, in particular, that of being a shrubbery that has flowers of a variety of bright colors growing on them.

That being said the large diversity in the rhododendron species calls into question their classification into one same species let alone into the same genus as azaleas.

Modern-day classification, which merged Azaleas into the Rhododendron genus contradicts usual botanist classifications that give primacy to the earlier classification.

The more logical merger would have been to place rhododendrons with the azalea genus, something that would have had historical precedent supporting it. This may have been the result of the larger amount of rhododendron species over those in the azaleas. There are over 850 species in the rhododendron genus, which are divided into three large groups:

  1. those with scaly leaves
  2. those with non-scaly leaves
  3. azaleas

Some botanists divide the last group of azaleas into two groups creating four large species groups in the rhododendron genus. Confusing matters even further botanists have found in recent years that deciduous azaleas and rhododendron are more similar amongst themselves than deciduous azaleas to evergreen azaleas.

In this sense, the official species classification that separates deciduous azaleas from rhododendrons is less accurate and could be changed. The problem lies in the very large and diverse group of rhododendrons more than in the fairly homogenous azalea group.

Rhododendrons, unlike azaleas, are restricted to the northern hemisphere. Some plants will only grow a few inches while some can be as tall as 27 meters. Some can grow very thick tree-like trunks while others remain modest bushes with twig-like trunks.

While the larger ones are mostly evergreen some of the species are deciduous and in some cases, rhododendrons can have both types of leaves on one trunk. These are called semi-deciduous and are a product of a plant being moved to a colder climate and the range of hardiness increases.

The leaves themselves can range widely as well from an inch to almost three feet. They can be thin or thick with smooth or rough surfaces. Some can survive arctic conditions and later in the year produce seeds for the summer. There is even one type of rhododendron that can survive as a desert plant.

Such diversity calls into question the very classification of all of them as rhododendron but their similarities of leave consistency, flower stamen, and DNA allows botanist to maintain the current classifications in genus and species. The large breath of rhododendrons is the best argument in favor of going against tradition and classifying azaleas under the rhododendron genus rather than merging rhododendron into the azalea genus.

Are they really opposites?

all azaleas are rhododendrons not all rhododendrons are azaleas

Both plants are native to Europe, North American, and Asia and can be either deciduous or evergreen, which means perennial or they may change their leaves depending on the dominant climate.

Asia is the main producer of evergreen azaleas and rhododendrons while deciduous plants are native to the United States with most originating in the southeastern part of the United States. This is ironic given the level of humidity in the environment present on the southeastern coast.

Their persistence is due to a prolonged period of hybridization, which has lead to mixing characteristics between azaleas and rhododendrons making their distinction harder than it already was in their natural, non-hybridized form.

How to distinguish an Azalea from a Rhododendron?

The connection with the rhododendron gives azaleas their volume but unlike other rhododendrons, they are one stem flowers. Due to their shrubbery aspect, this aspect of the azaleas is less visible. Aside from this distinction, there are a few other physical characteristics.

Starting with the leaves azaleas, unlike Rhododendrons whose leaves are thick and leathery, have thin, soft, and sometimes hairy leaves. Azaleas leave will never scale or dots something fairly common in rhododendron leaves.

Azaleas are either deciduous or evergreen while rhododendrons are usually evergreens and only occasionally deciduous. The flowers are the most distinguishing factor with azalea flowers usually being one stem flowers and counting with at most 5 or 6 stamens. Rhododendrons tend to have their flowers in clumps known as ‘trusses’ and have 10 or more stamens.

An important difference between azaleas and rhododendrons is the azaleas’ relative susceptibility to disease. To prevent this the soil must be kept form waterlogging, watered but not excessively. This one difference is central to choosing which of these shrubs to plant. Rhododendrons are more resistant to disease. This characteristic alone would encourage the amateur gardener in their first landscaping forays to choose a rhododendron over an azalea.

Other characteristics that are useful in identifying between azaleas are rhododendrons are the following:

  • Bloom time– azaleas tend to bloom in the early spring while rhododendrons need the warmer late spring temperatures to bloom. This does not apply to those shrub species that are repeat-bloomers. In both cases, though this information can be obtained at the nursery when purchasing the bulbs.
  • Flower shape– the well-known bell-shaped flowers belong to the rhododendrons while the funnel or tube-shaped flowers are azaleas. More telling is that azaleas will have one-stem flowers while rhododendrons have them in trusses or clumps of flowers not dissimilar to hydrangeas that look like balls of flowers.
  • Number of Stamen– these are the little twig-like pollen-filled stems found inside the flowers. The number of stamens is the deciding factor for more botanists when classifying a flower and in the case of the azaleas and rhododendrons it is central: the azaleas never have more than 5 or 6 while the rhododendrons tend to have 10 or more stamen.
  • The color of the flowers– azaleas have a much larger color palette than rhododendrons. Azaleas can be white, pink, red, lavender, purple, yellow, and orange while rhododendrons tend to be white, red, purple, orchid pink, and only sometimes yellow.
  • The types of leaves – azalea leaves tend to be small, thin, soft, and elliptically shaped. This is because most azaleas are deciduous as in not meant to last through hard winters. Rhododendrons, on the other hand, tend to be evergreen and can resist colder temperatures. This means their leaves are thicker, almost padded, scaly and sometimes with dots.

How to grow and care for Azaleas and Rhododendrons?

In hot climates, azaleas and rhododendrons can be planted year-round while in cooler climates spring is best.

Azaleas are used to decorate medium-sized to large gardens and to create arrangements or bouquets. Alongside hedges, it will bring bright colors in the spring and summer to any garden. The best way to have a healthy azalea is to prepare the soil properly before planting.

It needs to be well-drained and humus-rich which is slightly acidic to provide the right amount of nutrients. Since their roots tend to stay close to the surfaces mulching well and regularly is essential to help prevent the azalea from drying out.

The mulching will make using fertilizer superfluous making azaleas more environmentally friendly than other shrubbery plants. They are easy to care for because insects and diseases tend to bother them less than other plants.

Superficial roots are something azaleas and rhododendrons share for this reason when planting them never plant then deeper than they were originally planted when bought from a nursery. The best seasons for planting are in the spring or the fall. Space them 2 to 6 feet from each other to allow from easy, horizontal growth.

To prepare the soil it is good to add compost around the hole dug for planting, this is especially necessary is the soil is not naturally rich. Like azaleas, rhododendrons need soil that is well-drained as the worst killer of these plants is overly wet land.

Both plants grow more easily in Mediterranean countries rather than in places like England or Germany. This means NOT planting either shrub bulbs in clay soil, which collects and retains water. The best type of soil should be light soil rather than heavy soil. A second element that is needed is decomposed or composted pine bark. That is the best basis for mulching that helps both rhododendrons and azaleas grow.

Planting shallow means leaving the root bulb slightly above the edge of the soil, not covering the root bulb completely with soil. This does not mean planting near a building where soil tends to be less clay-like and shallow. Concrete makes the soil around it more alkaline and rhododendrons, and to some extent azaleas, are thrive on acidic soil.

To provide the right balance of acidic in a garden that has a house nearby it is best to plant them at the end of the garden near the fence rather than near the building itself. Before planting, and especially if the plants have been in pots for a long time, the roots need to be loosened by watering them outside of the container and before placing it in the ground.

Both plants benefit from regular, yearly pruning through having to remove dried or damaged branches is not common as they are sturdy shrubs. The best time for pruning is right after they have finished blooming. While pruning you have to be careful because these shrubs make their blooms in the prior year’s branches.

You need to prune right above the growth joints of the large leaves characteristic of the rhododendron. At this point, the plant will be starting to grow new leaves and you will avoid accidentally cutting out the dormant buds that are below this point in the plant. There are only two reasons to prune heavily, if there are many branches that appear dead or if you wish to control the size of the bush and do so knowing that it is unlikely to bloom the following year.

Why do people plant azaleas and rhododendrons? Should the flower be given as a gift?

Rhododendrons vs Azaleas

Azaleas are beloved shrubbery because they are easy to plant and maintain. They also grow quite quickly and easily producing abundant blooms early on. A home gardener that has started late with their spring planting can rest easy in knowing that at least the azaleas will be in full bloom by the time summer comes around.

Their shrubbery characteristics make them am an untraditional floral gift but they have been known to adorn bouquets, particularly the azaleas. Unlike most other flowers rhododendrons are best given as already potted plants that can then be transferred into the soil.

Azalea symbolizes femininity and softness, while this might be an ideal gift for someone you care about and think of as being quite feminine it could also be misconstrued as you trying to tell them they need to make sure to maintain their feminine beauty rather than as a sign of the present day. appreciation.

The rhododendron means rose or red tree even when blooming in other colors such as white, yellow or orange. This harks back to the original meaning of both azaleas and rhododendrons of low-growing rose. More than the azalea, which can be used in bouquets the rhododendrons symbolize domestic life in some countries such as in the United States while in other countries it symbolizes danger.

This latter is likely a result of rhododendrons containing toxins that can harm both animals and humans if ingested. Its predominance alongside garden hedges in countries such as England traditionally would be the result of both of the colors and of the toxins, which were a way of warding off intruders.

Whether you live in a warm climate or somewhere cooler choosing to plant an azalea or a rhododendron bush in your garden is likely to be the best long-term decision for creating your landscape.