Horticulture Magazine

Azalea Japonica Plant Care & Growing Tips

beautiful pink blooms of azalea japonica

Japanese Azalea Overview

Official Plant NameAzalea japonica
Common Name(s)Japanese Azalea
Plant TypeShrub / Houseplant
Native AreaJapan
Hardiness RatingOften H4
ToxicityToxic
FoliageLobed, evergreen leaves
FlowersVarious hues, commonly pink
When To SowMarch, April, May, June, September, October
Flowering MonthsMarch, April
When To PruneApril, May
Sunlight

Preferred
Full Sun or Partial Shade

Exposure
Sheltered

Size

Height
0.1 – 1M

Spread
0.1 – 1M

Bloom Time
April – June

Soil

Preferred
Chalk, loam, sand

Moisture
Moist but well-drained

pH
Acidic

Azalea japonica is a compact Azalea, in the Rhododendron family which can work well in beds or border, or containers with acidic conditions.

In this article, we will take a look at this attractive flowering shrub, share some cultivars to consider, and help you understand how to grow it successfully in your garden.

What is Azalea Japonica?

Azalea japonica, known as Japanese azalea, is a flowering shrub, usually evergreen, with a relatively compact form, glossy deep green leaves, and flowers which come in a wide range of colours.

pink japanese azalea flowers

It is a type of evergreen Rhododendron (though some varietals can be semi-evergreen and lose leaves in cold winters), within the Ericaceae plant family. They have smaller leaves than deciduous rhododendron.

Azaleas have been cultivated for centuries and more than 10,000 vibrant cultivars have been created, which means that there are plenty of options to consider when choosing one of these plants for your garden.

Azaleas are categorised under two sub-genera – Tsutsusi and Penthanthera. Japanese evergreen Azalea fall within the former sub-genus.

Azaleas are important in Japanese culture and Azalea festivals take place across the country each year, which are attended by many visitors.

The plants are a common sight in Japanese (and Japanese inspired) gardens around the world. Azalea japonica are sometimes also used for bonsai, carefully and delicately trained, and sometimes used as container plants or even houseplants.

Why Grow Azalea Japonica in your Garden?

Azalea japonica are ideal for a low maintenance garden. They are one of the most vibrant spring-flowering shrubs that can be grown in the UK, and provide their beautiful blooms for several weeks in April, May or June.

huge overgrown azalea and rhododendron bushes in a garden

Because of their spring flowering, they are also popular gifts for Mother’s Day and Easter.

These are a popular range of shrubs for acid-soil gardens, since these are ericaceous plants that like a more acidic soil pH. They can help you make the most of a garden with acidic soil conditions.

Even where there is not acidic soil, these small shrubs are pretty easy to grow in pots.

Azaleas can be interesting plants to grow. However, it’s important to note that they are poisonous to people, pets and livestock. So if you are considering growing them, this is something to bear in mind.

Japanese Azalea Varieties

There are a huge range of Japanese Azaleas to choose from. Some types to consider include:

  • Kurume – semi-dwarf Azalea hybrids which bloom prolifically.
  • Satsuki – compact Azaleas which bloom towards the end of spring. These azaleas have dwarf tree shape, with beautiful gnarled trunks. They were originally hybrids of Rhododendron Indicum and Rhododendron Eriocarpum, and have been cultivated in Japan for centuries, but in the UK only since the beginning of the 20th Century. These are not particularly hardy, but can be grown outdoors in milder parts of the UK, or as container plants to take indoors in winter in cooler regions.
  • Encore Azaleas – bloom from spring right through the summer months. These were developed by Robert C Lee in Lousiana.
  • Gartrell and Robin Hill Hybrid Azaleas – group of larger flowered hybrids developed by Robert Derby Gartrell in the late 20th Century.

Some interesting cultivars to consider include:

  • ‘Hot Shot’ – variegated leaves and striking red flowers.
  • ‘Silver Queen’ – variegated leaves and bright pink blooms.
  • ‘Summer Sun’ – Satsuki variety, rich red flowers.
  • ‘Robleza’ – Encore type, deep, intense red blooms.
  • ‘Robles’ – Encore, purple flecked lilac flowers.
  • Azalea amoena – Kurume variety, magenta-purple flowers, red autumn foliage.
  • ‘Hino Crimson’ – RHS AGM, small, deep red flowers.
  • ‘Mother’s Day’ – RHS AGM, bright red blooms.
  • ‘Addy Wery’ – RHS AGM, deep, rich red flowering.
  • ‘Iro Hayama’ – RHS AGM, white flowers with graduation to lavender or mauve.

Though of course there are many, many more Japanese azaleas to consider.

Where to Grow Azalea Japonica

One interesting thing to note is that Japanese Azaleas help purify indoor air from ammonia – from pet urine or household cleaning products. So this could be a good houseplant to consider growing in a container inside your home.

Many more compact cultivars are perfect for container growing, indoors, or outdoors with winter protection.

red scarlet japonica azalea plant in a white container on a patio

However, many Japanese Azaleas can also be a great choice for a UK garden. Many cultivars are H4 hardy, but take note that there are many Azaleas which are not as hardy and which are only options for outdoors cultivation in very mild and protected southern gardens.

Hardier cultivars will grow well in a fertile, rich, sandy or loamy soil which is moist and relatively moisture-retentive without becoming waterlogged.

They will thrive in a sheltered spot, in partial shade or full sun. Whether it is best to grow Azalea japonica in full sun or partial shade will depend on your location, and the type and cultivar you have chosen to grow.

Of course, the most important thing to remember is that, like other ericaceous plants, Azalea japonica does require acidic soil. The optimal pH is between 5 and 6 for most Azaleas.

Japanese Azaleas can work well in a planting scheme alongside other Azaleas, Rhododendrons, and Camellias.

By selecting cultivars carefully you can enjoy blooms over a much longer period – some can even work well as hedges. With Japanese Acers and other Japanese plants which like acidic conditions, they can be perfect for a Japanese inspired garden.

Planting

When planting Azalea japonica, it is important to take care not to damage the roots.

It is also important to plant the shrubs at the same level that they were at in their previous pot. Avoid planting them too deeply as they are intolerant of this.

The top of the root ball should be above the soil – take care to ensure that this is not buried or the Azalea may fail to thrive or even die.

If growing Japanese azaleas in containers, make sure you choose a container that is of a sufficient size, and one which allows free drainage.

Place crocks at the base to make sure water can pass through freely. Of course, you also need to make sure that you fill your container with ericaceous compost.

Care Guidelines

Azalea japonica are varied plants and some are much easier to care for and lower maintenance than others.

Once established, hardy types in your garden can be more or less left to their own devices. Less hardy types grown in containers, or indoors, will require a little more care.

Watering

Once established, most Japanese Azaleas can be relatively drought tolerant.

However, it is very important to water well during establishment, and to make sure that the soil (or potting mix in containers) does not dry out during dry spells.

When Azaleas are subjected to drought, they tend not to flower as well. Since they are shallow-rooted, they do need the soil to be kept moist.

Remember that you will have to water container-grown plants more frequently than those grown in the ground.

Mulching

To protect the shallow roots of these shrubs, and to reduce moisture loss, it is a very good idea to mulch well around your plants.

Choose an ericaceous mulch such as pine bark or pine needles to do so.

Mulching will also provide all the fertility Japanese azaleas need.

It is not usually necessary to provide any other fertiliser for these plants. In fact, fertilising too much can be counter-productive and these shrubs may not perform as well if you do so.

Pruning

Azaleas typically only need light pruning and Japanese azaleas may not really need to be pruned at all. As mentioned above, however, some azaleas are used as bonsai, and trained and trimmed into ornamental, decorative forms.

If light pruning is required, this should typically be undertaken just after the end of the flowering period.

Make sure you do not prune after buds for next years flowers begin to form as this would mean fewer flowers the following year.

There is more to discover about Japanese azaleas. But this guide should help you with the basics of choosing and growing these beautiful flowering plants.

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