Rhododendron Varieties: Planting and Disease Control

Rhododendron has been adored by many gardeners for generations because of its spectacular flowers.

Even though it is a short-lived one, along with its close relative, Azalea, become the favorite plants that have a four-season interest.

However, this variety will not be appealing except when it is in bloom.

Well, if you love this plant, you may want to do some judicious research and effort to find the varieties that offer beauty even beyond the bloom time.


What is Rhododendron?

Rhododendron are a large family of deciduous or evergreen shrubs or small trees that are primarily cultivated for their attractive blossoms.
Rhododendron Tree

The word rhododendron comes from the Greek language which means “rose tree”. Indeed, it is an acid-loving, woody shrub that has colorful flower clusters during the blooming time.

Moreover, these plants live in mild temperatures or damp climates.

There are thousands of varieties available but there is only one that you can have for your garden. Azalea is one of these types.

However, both of them have several distinct features. You can just see the five stamens and hairy rhododendron leaves on Azaleas.

Then, the height or spread of this plant is from 18 inches tall and wide to about twenty feet tall. It depends on the cultivar and species.

What about bloom time? Generally, the peak time happens in the middle of the spring season.

Otherwise, some species can get a bloom in March or July. The varieties that can go reblooming will get it again in the summer until the winter is coming.

Interestingly, these species have colorful flower clusters that are well-known as trusses.

In addition, you may find them in pink, white, deep crimson, yellow, reddish-purple, or blue color.

The Rhododendron Varieties

Rhododendron, meaning “red tree,” refers to the red flowers and woody growth of some species, but rhododendrons range in habit from evergreen to deciduous and from low-growing ground covers to tall trees.
Rhododendron and Camellia

If you plan to have these plants for the garden, you should know what type of varieties you are dealing with.

Thus, here are some recommended rhododendron flower cultivars that you should choose as part of your garden.

  1. Rhododendron Williamsianum

Rhododendron williamsianum is a compact, spreading small evergreen shrub, 1-1.5m tall, with neat rounded or heart-shaped leaves, bronze when young and glaucous beneath. Bell-shaped, soft rose-pink flowers, 5cm wide, are borne in small trusses in mid spring.
Rhododendron Williamsianum

This variety is also called Williams cultivar which grows to 4.9 feet tall and wide. The compact evergreen shrub is easy in the sun or shade.

Likewise, this flower species is a slow-growing one that is good enough to cultivate inside a large container.

Furthermore, it features rounded matt green leaves. Enjoy the beautiful pink bell-shaped roses in spring.

Additionally, this variety has gained an award of Garden Merit (Annual Award for Plants) in the UK.

  1. Rhododendron Calendulaceum

Calendulaceum commonly known as flame azalea, is an upright, loosely branched deciduous shrub that typically matures to 4-8' (infrequently to 10-15') tall and to 8-10' wide.
Rhododendron Calendulaceum

This species is also known as the flame Azalea which is native to North America. Although it would make a beautiful garden component, you should be careful with this species.

The leaves, blossoms, and stems of this cultivar are poisonous to humans.

Then, this deciduous shrub can go about 450cm tall. The showy flowers make flame Azalea the popular cultivated plant.

The blazing red shades, yellow, and orange blossoms are what you are going to get. Besides, it is well-adapted to the gardens.

  1. Rhododendron Augustinii

Rhododendron augustinii is a medium sized evergreen shrub with bright lavender blue flowers.
Rhododendron Augustinii

It is popular as Blue variety which is a large-growing cultivar. Its lavender-blue flowers make a beautiful color addition to any garden. This species is native to Tibet and central China.

The plants are quite suitable for shade or sun. Thus, the gardener reduces its size by selectively cutting it back. Otherwise, it could be a rhododendron tree.

  1. Rhododendron Keiskei

Rhododendron keiskei is a species of flowering plant in the heath family Ericaceae, native to Honshu, Kyushu and Shikoku in Japan. It is a low-growing, spreading evergreen shrub, reaching only 60 cm (24 in) tall by 1.85 m (6.1 ft) broad when mature.
Rhododendron Keiskei

This low-growing evergreen shrub is native to Japan. It can only reach about 24 inches tall and 6.1 feet wide when mature.

Also, this species features elliptic-shaped leaves with pale yellow flowers that you can see during the spring season.

The cultivation in East Coast gardens would be the best place for this variety. Because of its origin, this species is perfect for a rock or trough garden.

  1. Rhododendron Degronianum Ssp. Yakushimanum

Rhododendron degronianum is a species of rhododendron native to northern parts of Honshu, the largest island of Japan, where it grows at altitudes of about 1,800 meters.
Rhododendron Degronianum Yakushimanum

This variety is considered the most popular one. Also, it becomes the world’s most widely grown varieties. This evergreen shrub can grow about 8 feet in height.

Next, it has elliptic leaves with flowers in a funnel shape and pinks to white color.

Indeed, it is such a perfect plant for a garden that can tolerate being in relatively cold and heat conditions. Hardy to -15 degrees.

  1. Rhododendron Davidsonianum

Rhododendron davidsonianum, the concave-leaf rhododendron, is a species of flowering plant in the heath family Ericaceae that is native to the forests of Sichuan, China, where it lives at altitudes of 1,500–2,800 m.
Rhododendron Davidsonianum

It is a concave-leaf cultivar that is originated from China. This evergreen shrub has lanceolated glossy leaves.

Therefore, in the spring season, you can see it blooms bell-shaped flowers with pale pink or purple colors.

  1. Rhododendron Orbiculare

Rhododendron orbiculare, is a species of flowering plant in the heath family Ericaceae that is native to forests and slopes at an elevation of 1,400–3,500 m in northeastern Guangxi.
Rhododendron Orbiculare

This species has beautiful roses that always attract attention. The smooth round leaves and bell-shaped flowers with deep pink color.

Further, this compact shrub will grow to about 10 feet tall and wide. It grows best in light shade to avoid foliage scorch and maintaining mounding habits.

  1. Rhododendron Rupicola

This species is a much-branched shrub to 1.2m with broadly elliptic, ovate brownish leaves. The flowers are broadly funnel-shaped and purple-yellow in colour.
Rhododendron Rupicola

It is considered one of the best dwarf species for the rock garden. This variety can grow easily in a sunny location that has great drainage.

Moreover, the striking flowers with blue-purple to reddish-purple shade makes a beautiful addition to your garden.

  1. Rhododendron Luteum

Rhododendron luteum, commonly known as pontic azalea or honeysuckle azalea, is an upright spreading deciduous azalea that typically matures to 4-5' tall over the first 10 years, but may occasionally rise over time to as much as 9-12' tall.
Rhododendron Luteum

This one is Deciduous Azalea that would make a great ornamental plant for a sunny border. That bright yellow color of the flowers looks astonishing.

Besides, it smells good. You may witness the bright red splash of coloration during autumn.

  1. Rhododendron Degronianum

Rhododendron degronianum are found only in Japan, where they grow on hilltops and mountains on Honshu, Kiyushu and Shikoku Islands
Rhododendron Degronianum

This variable species is native to the mountainous area in Japan. It is such a perfect choice for your garden because this one would serve as interest during the non-blooming time.

So, your place would look lovely at any time.

Planting the Rhododendrons

Among the most popular companion plants for Rhododendrons and Azaleas are Kalmia latifolia (Mountain Laurel) and Pieris japonica (Japanese andromeda). Both species are medium-size evergreen shrubs with great flower interest and they provide a textural contrast to Azaleas and Rhododendrons.
Rhododendron Companions

There are a few things you need to know before planting these varieties. First, you should select the proper time to plant them.

So, when is the right time for planting? Well, according to the American Rhododendron Society, the suggestion to plant is based on the climate you have in your location.

In Hot climates, it is good to plant it in the fall season because it allows the root system of the plant to get a good establishment during the cool time.

Meanwhile, for those who are in mild climates, you can cultivate the plant all year round.

Moreover, for the garden in cold climates, it is perfect to begin the planting in the early spring season. A second choice is in the early fall.

So, where is the best place for these cultivars? Because they need good drainage and filtered shade, you have to plant them in an area that is protected from the wind.

Additionally, do not plant them near concrete or other hard things.

What about the soil? Any plant would thrive with acidic soil, it is pH 6 and lower because it is light and well-drained.

Also, it is full of organic matter that the rhododendrons need to grow healthy. You should amend the soil with something like fine bark and leaf mulch.

Instead, you may use some rhododendron fertilizer that you can purchase from the store. Do not use too much of it.

Consequently, it will burn the plants. The proper time to apply fertilizer is only when flower buds swell. It would be in early spring.

Tips and Tricks for Growing Rhododendrons

Evergreen rhododendrons are among the most popular flowering shrubs. They add bursts of color as specimen plants in any garden. Rhododendron blooms, which are larger than azalea blooms, usually open in May, and our plants bloom the first year.
Rhododendron Shrub

This one is like the cheat sheet you may wanna know to grow some varieties in your garden.

  • First thing first, you should choose the rhododendron bush plants that have at least 4 main branches for the base.
  • Then, you have to purchase the plants that are already bloom, so you will know what color of flowers to expect for the garden.
  • Plant them in a sheltered space that does not get direct sun and wind. It would make some delicate leaves burnt.
  • Do not plant it in a deep shade because this plant will need some sunlight for the flowers to grow.
  • There is no need to do the deadheading of spent flowers. But, you can do it easily and gardeners would love it.

Common Diseases

Rhododendrons (including deciduous azaleas) may be attacked by several diseases, causing unsightly foliage or a lack of flowers.
Rhododendron Disease

There are some diseases that you may deal with when having these rose trees. They are as follow:

  • Bud Blast. The brown flower buds will die while still adhered to the branch.
  • Petal Blight. The spots on petals occur under wet conditions.
  • Powdery mildew. An actual fungus grows right on the lower leaves in form of powder.
  • Gall. The pale, swollen, and distorted leaves on Azaleas.
  • Leaf Spots. More or less round spots on the leaf surfaces. It occurs on evergreen species.
  • Rust. Discolored spots on the surface of upper leaves.
  • Silver Leaf. Dieback branches because of fungus.

Controlling the Diseases

Powdery mildew on rhododendrons is a fungal infection of the leaves. On rhododendrons, the disease often fails to develop the distinctive powdery white growth normally associated with powdery mildews.
Rhododendron Powdery Mildew

There are two ways of dealing with the diseases, non-chemical or chemical controls. Well, if the plants have bud blast, powdery mildew, leaf spots, and galls, always go with the organic or homemade ones.

For the bud blast and most diseases, you have to remove the infected things or fungus attached to the plants.

If the issues persist, you may wanna get some chemical materials or products and apply them to your infected plant.

You can use some tools like a sprayer to effectively control the spread and growth of the diseases. Ensure that you pay attention to the labels and guides.


Rhododendron offers beautiful flowers in a form of evergreen shrubs. Numerous plant varieties give a colorful cluster of blossoms. They would surely make a great attraction to your garden.

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