Azalea Japonica 101: How to Grow Azalea Japonica Shrubs
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:
- Evergreen – keeps its leaves in the winter.
- Flowers from April to May.
- Easy to maintain and fairly slow-growing.
- Can be grown in pots.
- Suffers from few problems.
In 10 years, most azalea japonicas grow to:
Height: Up to 1m (3′)
Width: Up to 1m (3′)
Evergreen: Keeps its leaves throughout the winter
Slow growing and doesn’t require hard pruning
Easy to grow and maintain
Asia, Europe and North America
In a spot with well-drained soil, ideally in partial shade
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
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
Many spring and summer shrubs as well as spring-flowering bulbs such as tulips and alliums
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
Typically in April and May
Azalea Japonica: Common Questions Answered
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?
Azaleas should be grown in a spot with partial shade or dappled sunlight. They can be grown in full sun but would require constant watering to keep the soil moist, something which isn’t practical for most of us.
Keep azalea japonicas away from tree roots, south-facing walls, hot patios and dry areas of the garden.
How should the soil be prepared?
Azalea japonicas are acid-loving shrubs and respond well to leafmould or ericaceous compost added to the hole before planting and yearly afterwards.
We suggest soil testing to ascertain the ph levels of the soil. This can be done off-site or via a testing kit purchased online.
Plant shallow with the top of the rootball at ground level, azalea japonica won’t respond well to deep planting.
Do azalea japonicas require lots of water or fertiliser?
Water is crucial as azalea japonicas struggle in dry soils.
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 bud initiation.
Fertiliser must be ericaceous and preferably slow-release. The best time to apply is in March and immediately after flowering has finished – this assists with bud formation.
How tall and wide will azalea japonicas grow?
Azalea japonicas are the smaller of the varieties and usually grow to between 60cm and 100cm in both height and width.
Should azalea japonicas be pruned and deadheaded, and if so, how and when?
Pruning is optional and is usually done for aesthetic purposes, but azalea japonicas should be deadheaded immediately after flowering, this is especially important on younger or weaker plants.
If you need to prune, do so straight after flowering and before the buds for next year have set, which is usually at the end of June.
Are there any pests and diseases to worry about?
Azalea japonicas are tough shrubs that are resistant to most common garden pests and diseases.
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 rarely cause considerable danage.
Lacebugs may affect azaleas; the RHS site has advice on treating them.
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 the UK, azalea japonicas bloom 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 pests resistance.
The best way to propagate azalea japonica is via stem cuttings.
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.
Are azalea japonicas beneficial to wildlife?
While they provide shelter for butterflies and insects, they usually flower before bees and most other pollinators are in full swing so are of limited use to them.
Can they be grown in pots?
Yes, 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, azaleas should be repotted every three to four years.
Growing Azalea Japonica: 8 key Points
Here are eight key points anyone growing azalea japonicas should consider:
- Azalea japonicas are evergreen and more compact (up to 90cm/3′) than their deciduous cousins (up to 150cm/5′).
- Choose a spot in partial or dappled shade for best results.
- Watch out for hot patios, walls and pots where the soil could dry out and cause problems.
- Plant shallow – the hole should be twice as wide as it is deep, and don’t bury the crown under the soil.
- Don’t forget that azaleas are acid-loving plants, so they prefer ericaceous compost, leafmould and pine needle compost etc. So dig in some ericaceous compost when planting and mulch in again every year or two. Fertilise with a suitable slow-release feed in March and again immediately after flowering.
- Look at the maximum size of mature plants and leave enough space for the azalea to grow into.
- Pruning is entirely optional and is only done for aesthetic purposes or to keep an azalea under control.
- Deadheading is recommended but should be done immediately after flowering, so energy is directed to new shoots, which will be solid and healthy and will hold large blooms next year. Failure to deadhead will result in energy being used to create seedpods, and the new stems could be weaker. Deadheading can benefit any azalea of any age but especially younger or weaker plants.
How to Grow Azalea Japonicas in Pots
Azaleas can be grown successfully in pots provided the gardener is prepared to put in the necessary time to maintain and care for them.
They also need to be potted up to bigger containers every three years or so.
Both evergreen and deciduous azaleas can be grown in pots as the roots stay relatively shallow.
The key is to plant shallow and don’t bury the stem.
Pot Size and Shape
Choose a pot that’s approx 75mm wider than the existing tub. Shallower but wider pots are more suitable than narrower deeper types, and drainage is essential, so holes should be located at the bottom.
Depending on the height of the azalea and on the potential for it to topple over, you may need to choose a heavy container, although very tall azaleas are not best suited to pots.
Every three years, the azalea should be moved to a slightly larger pot up to 75mm wider. The best time to move an azalea is after flowering; just give it a light prune to shape and water well the night before. If possible, locate the pot in a cooler location for a few weeks, so the azalea isn’t stressed.
Ericaceous compost should be used, and if it’s very fine, add composted bark to the base and mix in some with the compost. This will help with aeration and drainage.
A yearly organic mulch will benefit azaleas in pots but be careful not to bury the stem.
Bark chippings and pine needles are perfect mulches for azaleas but avoid pea shingle, slate and stone as these conduct heat and compress the compost underneath.
Potted azaleas respond well to a twice-yearly feed with a slow-release fertiliser, ideally in pellet form.
March and June are ideal feeding times, and the pellets can be sprinkled on the pot’s surface.
Azalea Japonicas can and will struggle if the compost stays dry during the summer months.
How much water the plant requires will depend on its location; hot patios and walls can radiate heat which dries out the compost. The azalea may need twice-weekly watering in hot areas, while an azalea in a cooler spot will only need watering once a week.
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.
You can include water-retaining gel into the compost if you wish; this will help azaleas survive in warmer locations.
Azalea Japonica Companion Plants
Azalea Japonica sits very well with a wide selection of spring-flowering bulbs, including late daffodils, tulips of all varieties and alliums.
Ferns, grasses, hostas and box hedges can also add background colour and interest to larger borders and are perfect companions for azaleas grown in the shade.
Also, consider forget-me-nots, irises and lilac.
Hydrangeas flower after azaleas, but they go well together as both prefer moist soil and they work well in a multi-season border.
Common Azalea Plant Problems
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 most of the issues can be avoided by following these steps:
- Choose the best spot for your azalea, which will be in dappled shade, don’t grow in full sun, or you’ll be forever struggling to keep the soil moist.
- 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.
- 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.
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This guide to azalea japonicas for late spring and early summer colour was created by Daniel Woodley here at DIY Gardening and was last updated in February 2022.
Daniel is a keen gardener who also manages a large residential landscape in addition to his own mid-size garden.
He also enjoys experimenting with vegetables and fruits in his garden but with varying success!
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