Azalea japonica, the Japanese azalea

Azalea japonica is a small heath shrub that provides evergreen, bushy growth and very beautiful flowers that range from pink to red, purple and white. 

Key Azalea japonica facts

NameAzalea japonica
Scientific nameRhododenron Azaleastrum Tsutsusi
Family – Ericaceae
Type – shrub

Height
 – 3 ½ to 6 ½ feet (100 to 200 cm)
Exposure – part sun and shade
Soil – acidic, heath soil

Foliage
 – evergreen
Flowering – April-May

Since it can grow up to 5 to 6 ½ feet (1.5 to 2 meters) tall, depending on the species, Azalea japonica is an ideal shrub to fill in a heath plant flower bed.

Planting Azalea japonica

It is important to not over-expose your Azalea japonica to sunlight, so favor a spot that is partly shaded.

  • Well-drained soil is essential.
  • Adding heath soil is necessary.

To generate spectacular blooming, add heath plant fertilizer.

Pruning and caring for Azalea japonica

Pruning Azalea japonica

It isn’t necessary to prune the plant. Nonetheless, if you wish to balance the shape or reduce the size of your azalea, wait for blooming to be over.

  • Favor light and delicate pruning rather than drastic cutting back.
  • Remove wilted flowers regularly (deadheading) to spur appearance of new buds. This will also direct the plant’s energy to growing new branches.

Watering Azalea japonica

The surface-most roots of Azalea japonica are the most thirsty roots, and they require frequent watering in spring and especially in summer.

  • To reduce watering frequency, mulch the base of your Azalea japonica with maritime pine bark, this will retain moisture and cool the soil.
  • After a couple years, your azalea japonica will do fine without any watering, except in case of prolonged dry spells or heat waves.
  • If the water is hard in your area, do your best to recover rainwater: hard water tends to reduce soil acid levels, which Japanese azalea loves.

Growing your Japanese azalea in pots or containers

Pink blooming Azalea japonica in a tin pot set on a tableThe shallow root system and small size of Azalea japonica makes it an ideal candidate for container growing on a balcony or terrace. Prepare heath plant soil mix and ensure the pot or container is wide enough.

Depth of the container or pot isn’t an issue, to the point that you can save soil by filling the lower half with rocks or hollow implements.

Growing Azalea japonica as a bonsai

Azalea japonica satsuki covered with flowersSince Japanese azalea has long been grown as a bonsai under its more specific ‘Satsuki’ and ‘Kurume’ varieties, why not try it out yourself?

  • use soil that is rather acidic, as for heath plants, and avoid lime
  • water enough that the soil remains moist but never wet
  • use organic azalea fertilizer, but only during the growth phase
  • prune your bonsai Azalea japonica just after the blooming
  • if you want to shape it with wire, proceed with caution because branches break easily

Repot your Azalea japonica bonsai very carefully every two years. Root systems tear apart easily so again, proceed with caution.

Azalea japonica diseases and pests

Your Japanese azalea might have to fend off red spider mites, leaf gall, and root rot.

Leaf gall on Azalea japonica

If leaves start swelling, curling over and growing fleshy bulges, you’re facing a case of leaf gall.

This is a fungal disease induced by the Exobasidium vaccinii germ.

  • Remove infected leaves immediately and burn them.
  • If it persists, spray a natural fungicide like horsetail tea.

Root rot on Azalea japonica

If the trunk and roots start taking on a dark red or brownish color and that leaves shrivel up and fall off, you’re facing a case of root rot caused by the Phytophthora bacteria.

  • It’s usually too late to cure the plant at this stage.
  • Pull it out to protect neighboring plants
  • To avoid this fungus, ensure the soil drains very well, and occasionally spray the ground with a natural fungicide.

Different types of Azalea japonica varieties

We’ve mentioned two varieties often used for bonsai, the Satsuki and the Kurume, which are hybrids that have been carefully propagated through cuttings. But there are many more types of Azalea japonica to be explored!

  • Satsuki – often called ‘late-blooming’ because it only blooms at the end of spring (May to June).
  • Kurume – semi-dwarf hybrid that blooms profusely.
  • Encore – developed by a Lousiana grower, Robert C. ‘Buddy’ Lee. Bloom from spring to fall.
  • Robin Hill and Gartrell hybrids – also a group of Japanese azalea hybrids grown by Robert Derby Gartrell in the late XXth century. Larger flowers, very hardy.

With over uncountable varieties, it’s guaranteed that an Azalea japonica exists that hits your sweet spot!

The key point that brings Azalea japonica specimens together within the Azaleastrum section of the Rhododendron family it the fact that they’re evergreen, hardy and have leaves and flowers that are smaller than actual rhododendron shrubs.

How is Azalea japonica different from other azaleas?

Japanese azalea is said to be an evergreen azalea. This means that it keeps its leaves in winter and only sheds older leaves when newer leaves have taken over, except in cases of really deep cold weather. Regular azaleas are often deciduous and will lose their leaves every year in the cold season, even in mild winters.

Additionally, azaleas of the deciduous type have larger, longer leaves, whereas Japanese azaleas have smaller leaves that are at most 2 inches (5 to 6 cm) long.

All there is to know about growing Azalea japonica

This shrub is actually a small-flowered rhododendron, and it stands out in spring thanks to its beautiful bright and colorful bloom.

Azalea japonica grows into a nice round shrub that highlights its generous blooming and the deep green of its leaves.

Note that Azalea japonica might lose its leaves in case of strong frost spells, but this won’t have any incidence on the plant itself.

  • Azalea japonica can resist freezing temperatures down to around -4° to 5°F (-15 to 20°C).

When grown indoors, Azalea japonica helps purify your indoor air from ammonia, a common smell that arises from house-cleaning products and pet urine.

Smart tip about Azalea japonica, the Japanese azalea

Amazing backlit picture of purple flowered azalea japonica blaue Donau varietyTo enhance shrub growth, mulch the ground around it to retain moisture.

Favor any acidic mulch such as pine bark mulch.


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Azalea japonica shrub in garden shared by brx0 under © CC BY-SA 2.0
Pink flowering azalea japonica shared by Elize Eveleens/Bloemenbureau Holland
Azalea bonsai shared by Cowtools under © CC BY-NC 2.0
(plant nurtured by the National Arboretum, Washington DC, USA)
‘Blaue Donau’ Japanese azalea shared by Paul van de Velde under © CC BY 2.0

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