Azalea Japonica 101: How to Grow Azalea Japonica Shrubs

Written by Hannah Miller. Reviewed and Fact Checked by Elizabeth Smith. Published to Spring Plants. Updated: 19th February 2023.

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Bursting with spring colour, azalea japonicas will make a statement in any garden and are tough enough to be self-reliant once established, they also look stunning in pots and mix well with other shrubs and spring-flowering bulbs.

If you’re looking for a spring shrub that always puts on a good show, give azalea japonica a try.

Key plant details:

  1. Evergreen – keeps its leaves in the winter.
  2. Flowers from April to May.
  3. Easy to maintain and fairly slow-growing.
  4. Can be grown in pots.
  5. Suffers from few problems.

Size

In 10 years, most azalea japonicas grow to:

Height: Up to 1m (3′)

Width: Up to 1m (3′)

Type

Type

Evergreen: Keeps its leaves throughout the winter

Growth icon

Growth

Slow growing and doesn’t require hard pruning

Difficulty

Easy to grow and maintain

Native

Asia, Europe and North America

Location

In a spot with well-drained soil, ideally in partial shade

Sunlight

Can survive in a sunny spot but only if the soil is kept reliably moist, otherwise grow in partial or dappled shade for best results

Hardiness

US zone 4-8 and hardy in all parts of the UK

Water & Feed

If grown in ideal conditions, water once a week in the summer. If grown in dry soil or in full sun, water two times a week. The soil in pots should be kept moist in the summer. Feed with leaf mould or ericaceous compost

Companions

Many spring and summer shrubs as well as spring-flowering bulbs such as tulips and alliums

Planting

Plant at any time of the year provided the ground isn’t frozen. Dig in plenty of leafmould and/or ericaceous compost to a hole that is twice its depth in width

Flowering

Typically in April and May

Azalea garden in Japan
Red Azalea Japonica

Azalea Japonica: Questions Answered by an Expert

Despite having experience growing azalea japonica at my previous property, I asked qualified horticulturist Elizabeth Smith to answer some questions for our readers:

How and When are Azalea Japonicas Sold?

Azalea japonicas are usually sold in pots between 2 and 7.5 litres and are available throughout the year.

Where is the best location for azalea japonica?

I’ve grown azaleas for years and based on my experience, I feel the best location would be in a spot with partial shade or dappled sunlight. I have grown them in full sun in pots but I had to water them more frequently.

I suggest keeping azalea japonicas away from tree roots, south-facing walls, hot patios and particularly dry areas of the garden.

How should the soil be prepared?

Azalea japonicas are acid-loving shrubs and I’ve found that they respond well to leafmould or ericaceous compost added to the hole before planting and yearly afterwards.

If you’re unsure of your soil type, I suggest soil testing to ascertain the ph levels of the soil. This can be done off-site or via a testing kit purchased online.

One tip I’ve learnt over the years is to always plant shallow with the top of the rootball at ground level as azalea japonicas won’t respond well to deep planting.

Do azalea japonicas require lots of water or fertiliser?

Water is crucial, as I witnessed azalea japonicas struggle in dry soils, including in some small pots.

The ground should be kept moist but not waterlogged throughout the growing season and also at the end of June, which is when the all-important flower buds form.

Mulch should be ericaceous and any fertiliser preferably slow-release, I’ve never used those high-dose feeds which I feel are a waste of money. The best time to apply is immediately after flowering has finished, as this assists with bud formation.

How tall and wide will azalea japonicas grow?

Azalea japonicas are the smaller of the varieties, and mine grew to between 60cm and 100cm in both height and width.

Should azalea japonicas be pruned and deadheaded, and if so, how and when?

I’ve never felt that pruning is required, and it’s usually done for aesthetic purposes, but I know that young azaleas will benefit from deadheading immediately after they’ve finished flowering. I have been told that this helps the new buds form, which are crucial for next year’s growth.

If you need to prune, I suggest doing so straight after flowering and before the buds for next year have set, which in my garden, is usually in June.

Are there any pests and diseases to worry about?

The azalea japonicas at my previous property were tough shrubs, and I don’t recall having any issues worth noting.

Here are a few things to look ouot for though:

Pests

Vine weevil is a concern for azalea growers, and while the beetle only causes cosmetic damage, the females can lay up to 2000 eggs which form grubs that feed on the roots of all azaleas.

The RHS website has several tips on how to control this common pest.

Caterpillars are common but in my garden they rarely caused any damage.

Lacebugs may affect azaleas; the RHS site has advice on treating them but I never had any issues.

Diseases

Bud blast – look for small black, hairy growths that look like small hedgehogs. Affected plants may refuse to flower, and the damage may look similar to frostbite. The best treatment is to remove the affected buds before the disease can spread.

Powdery mildew affects azaleas and can be treated by following these tips.

When do azalea japonicas bloom and how long for?

In my previous garden in Surrey UK, the azalea japonicas bloomed for about three weeks in April and May.

Can azalea japonicas be propagated?

Seeds won’t produce shrubs that are true to the original plant and may lack disease and pest resistance.

I’ve had success propagating azalea japonica is via stem cuttings, they put on roots quickly, and I kept them potted for two years before moving them into the beds.

Follow the steps on this page if you want to propagate this popular shrub.

Are azalea japonicas toxic or harmful to humans and pets?

All parts of azaleas are toxic to cats, dogs, wildlife and humans.

Source.

Are azalea japonicas beneficial to wildlife?

While they provide shelter for butterflies and insects, in my garden they flowered before bees and most other pollinators were in full swing, so were of limited use to them.

According to several sources, the nectar from the azaleas is also toxic to bees, and they are included on several lists of plants to avoid.

Can they be grown in pots?

Yes, and I have done so with success, but be aware that azaleas hate dry, hot parts of the garden so a clay pot on a sunny, scorching patio might not be the best spot, although this can be mitigated by consistent watering to ensure the soil stays moist.

For best results and based on my experience, azaleas should be repotted every three to five years.

[x4] Dwarf Japanese Azalea Collection | Variety-Pack | Evergreen Shrubs | Pot Plants
1 X Orange Azalea Japanese Evergreen Shrub Hardy Garden Plant in Pot
[x4] Dwarf Japanese Azalea Collection | Variety-Pack | Evergreen Shrubs | Pot Plants
1 X Orange Azalea Japanese Evergreen Shrub Hardy Garden Plant in Pot
[x4] Dwarf Japanese Azalea Collection | Variety-Pack | Evergreen Shrubs | Pot Plants
[x4] Dwarf Japanese Azalea Collection | Variety-Pack | Evergreen Shrubs | Pot Plants
1 X Orange Azalea Japanese Evergreen Shrub Hardy Garden Plant in Pot
1 X Orange Azalea Japanese Evergreen Shrub Hardy Garden Plant in Pot

Growing Azalea Japonica: 8 key Points

Here are eight key points anyone growing azalea japonicas for the first should consider:

  1. Azalea japonicas are evergreen and more compact (up to 90cm/3′) than their deciduous cousins (up to 150cm/5′).
  2. I’ve had great results with them in partial or dappled shade.
  3. Watch out for hot patios, walls and pots where the soil could dry out and cause problems, this an issue I have seen first-hand.
  4. Plant shallow – the hole should be twice as wide as it is deep, and don’t bury the crown under the soil.
  5. Don’t forget that azaleas are acid-loving plants, so they prefer ericaceous compost, leafmould and pine needle compost etc. I always dig in some ericaceous compost when planting and mulching again yearly. I usually fertilise with a suitable slow-release feed in March and again immediately after flowering.
  6. Look at the maximum size of mature plants and leave enough space for the azalea to grow into.
  7. Pruning is entirely optional, and I’ve only ever done it for aesthetic purposes or to keep an azalea under control.
  8. I recommended deadheading immediately after flowering, so energy is directed to new shoots, which will grow solid and healthy enough to support large blooms next year. I’ve seen before that if one fails to deadhead, the azalea will spend energy on seedpods and not stem growth. Deadheading can benefit any azalea of any age, but from my experience, younger or weaker plants get the most from it.

How to Grow Azalea Japonicas in Pots

I have successfully grown azaleas in pots, and provided the gardener is prepared to put in the necessary time to maintain and care for them, there is no reason why they can’t thrive there.

I suggest moving the azaleas to a bigger container every three to five years or so.

I have seen both evergreen and deciduous azaleas grown in pots as the roots stay relatively shallow.

If I could give you only one tip, it would be to plant shallow and don’t bury the stem.

Pot Size and Shape Suggestions

Choose a pot that’s approx 75mm wider than the existing tub. I’ve found that shallower but wider pots are more suitable than the narrower, deeper types, and drainage is essential, so there should be enough holes at the base.

Depending on the height of the azalea and its potential to topple over, you may need to choose a heavy container, although very tall azaleas are not best suited to pots.

Every three to five years, the azalea should be moved to a slightly larger pot up to 75mm wider.

I’ve found that the best time to move an azalea is after flowering. I would give it a light prune to shape and water well the night before. If the weather is hot and dry, I suggest locating the pot in a cooler location for a few weeks so the azalea isn’t stressed.

Compost

I always use ericaceous compost and if it’s very fine and silty, I would add composted bark to the base and mix in some with the compost. This will help with aeration and drainage.

Mulch

I suggest applying an organic mulch each year but be careful not to bury the stem.

Bark chippings and pine needles are perfect mulches for azaleas but avoid pea shingle, slate or stone as these conduct heat.

Feed

I’ve found that potted azaleas respond well to a twice-yearly feed with a slow-release fertiliser, ideally in pellet form.

I always fed mine in March and June, and the pellets can be sprinkled on the pot’s surface or worked into the soil.

Watering

Azalea japonicas can and will struggle if the soil stays dry during the summer months. I have seen this with younger specimens but less so with established ones.

How much water the plant requires will depend on its location; hot patios and walls can radiate heat which dries out the compost. A potted azalea may need twice-weekly watering in hot areas, while an azalea in a cooler spot will only need watering once a week in the summer, if that.

A deep drench once to twice a week is far better than daily light watering, and rainwater is far better than tap water, especially if you live in a hard water area.

Westland Water Saving/Retention Gel, 250 g
50 litre bag of RHS endorsed Melcourt composted fine bark - ideal for improving your soil
Westland Water Saving/Retention Gel, 250 g
50 litre bag of RHS endorsed Melcourt composted fine bark - ideal for improving your soil
Westland Water Saving/Retention Gel, 250 g
Westland Water Saving/Retention Gel, 250 g
50 litre bag of RHS endorsed Melcourt composted fine bark - ideal for improving your soil
50 litre bag of RHS endorsed Melcourt composted fine bark - ideal for improving your soil

Azalea Japonica Companion Plants

At my previous property, I experimented with various different companion plants for azalea japonicas but there are so many to choose from, the sky really is the limit.

I’ve found that ferns, grasses, hostas and box hedges add background colour and interest to larger borders. Also, consider forget-me-nots, irises and lilac.

Hydrangeas flower after azaleas, but I think they go well together as both prefer moist soil and they work well in a multi-season border.

Common Azalea Plant Problems

My experience has taught me that azaleas are tough shrubs that require very little attention if grown in a suitable location with good drainage.

The Plant Addicts site has published a list of azalea problems and diseases you may encounter, and their guide is worth reading, but I feel most of the issues can be avoided by following my advice below:

  • Choose the best spot for your azalea, which will be in dappled or part shade, don’t grow in full blazing sun if you can avoid it, especially if it’s potted.
  • Amend the soil if grown in dense, clay-based soil.
  • Avoid waterlogged soil.
  • Water at the base of the plant and not overhead as splashing transfers diseases from leaf to leaf.
  • Mulch yearly to keep the soil acidic but don’t bury the stem, I have seen azaleas die because the gardener buried the stem.
  • Practice good hygiene with secateurs and other tools.
  • Be careful where you locate pots, as the soil within them often dries out quickly when in direct sunlight or placed on a hot patio.

Our Expertise: Backed by a Qualified Horticulturist

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This guide was reviewed and fact-checked by qualified horticulturist Elizabeth Smith.

Explore: Elizabeth's profile and qualifications.

Meet The Author: Hannah Miller

Hannah is a keen gardener who grows organic fruit and vegetables in her Surrey garden and is moving towards a more sustainable lifestyle. 

She is also the proud grower of a dahlia and herb garden.

Hannah worked for the NHS for 12 years but also has a level 3 qualification in horticulture and is currently studying for her level 4.

More About Hannah Miller

Hannah Miller

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