Growing Azaleas — Care Of These Beautiful Flowering Shrubs

Last Updated on May 29, 2021 by Grow with Bovees

Azaleas are one of the most popular shrubs in the United States, and with good reason. Their flowers are bright and colorful, and their shrubbery is attractive year-round.

Growing azaleas is one of the most rewarding tasks in the garden, they are the most beautiful shrubs for early spring color.

The range of azalea species includes both evergreens and deciduous. The plants grow up to about one meter high, but by trimming them every year after they have finished flowering, they can be kept to a smaller size.

It may not be necessary to trim azaleas for several years since they are slow-growing.

You can grow azaleas both outdoors and in, but, as with many plants, there are some factors to consider when choosing where to plant them. As a first step towards growing azaleas in the garden, choose an area where they will receive as much sunlight as possible, at least four hours a day.

Azaleas Form

Deciduous and evergreen shrubs.

Most varieties grown in gardens reach a height of between 2 and 6 ft (1.83 m) with a similar spread.

They are bushy and usually symmetrical in shape.

Azalea Flowers

The flowers are generally trumpet-shaped with rather slender, elongated corolla tubes, and they appear in small or large clusters at the ends of stems. In some species the flowers are distinctly two-lipped, while in others the petals are frilled at the edges.

The flowering period extends from early winter to mid-spring, and the flowers are to be had in a large variety of shades of every color except blue.

The leaves are, as a rule, narrow and oval or linear and carried in whorls.

Some species have leaves which assume lovely golden to bronze tints in the autumn.

Use of Azaleas

There are probably no flowering shrubs as beautiful as azaleas, and a garden which has little else apart from these and roses is picturesque throughout the year.

Select early, mid-season and late varieties for a blaze of color from late autumn to mid-spring.

When the plants are not in flower, the mass of dark and light green leaves and the pretty shape of the shrubs make them an asset in any garden.

In Europe, they are forced into early bloom to provide flowers during winter, and they are sold to householders in small pots in much the same way as potted hydrangeas.

They may be grown in tubs on the veranda or shady patio as well as in the open garden.

Group them with other acid-loving plants such as hydrangeas, Kalmia latifolia, Vaccinum arboreum, Pieris japonica and camellias.

How To Plant Azaleas

Azaleas have definite preferences as regards soil pH and situation.

If they are provided with the right kind of acidic soil, adequate moisture and partial shade they will thrive, but if they are planted in the wrong kind of soil they will die or remain stunted and refuse to flower.

The soil must be distinctly acid and fairly loose, and they must have an abundance of water particularly from mid-summer to the time when they flower.

In their native haunts they are found growing exposed to full sunshine, but it has been found that really intense sunshine is likely to retard growth and to scorch the flowers, so it is better to plant them in partial shade under deciduous trees.

Hot dry winds are likely to sear the blooms and if such weather prevails during their flowering period they should be sprayed regularly to add humidity to the air about them.

Azaleas are surface-rooting plants and are therefore inclined to suffer if the soil is baked by the sun.

For this reason it is advisable to keep the ground mulched at all times, the mulch being 4-5 in. thick.

A mulch of oak-leaves or fallen pine-needles is of great benefit to them on account of the acidity which the decaying leaves impart to the soil.

The soil in gardens that are not acidic may be amended with soil suitable for planting azaleas in the holes.

Dig holes about 4 ft (1.22 m). Square and 2 ft (0.61 m) in depth and fill them with well-rotted leaf-mold. Oak leaf-mold is particularly good.

Some nurseries keep a special soil mixture suitable for this purpose. If azaleas are to thrive and provide an abundance of bloom it is absolutely imperative that the soil in which they are planted should be naturally acid or made acid.

Most species of azaleas do best in soils which have a pH value of 4.5 to 5.5.

It must be remembered too, that soils may lose acidity through one cause or another, in the same way as they lose fertility.

It may be found that after growing well for a few years the azaleas begin to show signs of being unhappy.

The first sign of this is usually streaks of yellow on the leaves. Since azaleas are long-lived plants it is worth studying their idiosyncrasies and providing them with optimum growing conditions.

Fertilizing Azaleas

Azaleas growing in their natural state receive nourishment from decaying vegetable matter which is always present, and it is far better to provide them with nutrients in this way than to try to force them into better growth by applying commercial fertilizers, as most of the ready mixed ones are quite unsuitable.

Well-decayed stable manure may be used, but in applying it, be careful to avoid damaging the surface roots, and fork it only very lightly under the soil.

Azaleas start making bud-growth during summer and it is most essential that they should be kept well watered from this time onwards until their flowering season ends.

Watering Azaleas

They grow only in acid soil and should be watered regularly during the dry months of the year.

Because of the dense arrangement of their leaves, overhead sprinklers are not recommended as most of the water remains on the leaves and little penetrates to the roots of the plant.

The roots are near the surface and, where it is not practical to water well regularly, it is advisable to mulch the soil with an acid material, such as dropped pine needles or composted oak leaves.

Should the leaves of azaleas show yellowing it is an indication that the soil is not acid enough and the plant should be treated with iron chelates obtainable from plant supply stores.

Azaleas In Pots

If you have azaleas that were purchased in pots, once the potted azaleas have finished flowering, they should either be planted out in the garden or repotted into pots about two sizes bigger than the original ones.

Use a ready-mixed potting compost and then add some extra peat to make it more acid.

If the plants are to be kept in pots, you must make sure that they are in a shady place and that they are never allowed to dry out.

Should You Dead Head Azaleas?

Yes, take off the dead flowers.

By removing dead flowers — and the immature seed pods they contain — you encourage the plant to direct its energy into building up strength for the following year rather than into producing seeds, which is what it would do in the wild.

Take care, though, not to damage the young leafy shoots that originate close to the bases of the dead flowers.

Leave the dead flowers and their seed pods on the plant only if you want seed for raising new plants.

Bear in mind, though, that raising azaleas from seed is worthwhile only with true species. Most azalea varieties are hybrids and won’t breed true from seed. If you want seeds, leave only a few pods: more will weaken the parent plant.

Why Is My Azalea Not Flowering?

Azaleas often fail to flower well if they have been allowed to dry out during the summer months.

This is the time when they set their flowers for the following season and these will not form if the plants become hot and dry.

It is not just a question of keeping the soil damp, as the plants also like a moist atmosphere.

So when watering, use the spray nozzle to spray the foliage as well as the soil surface and, to help keep the plants cool during very dry, hot weather, spray the leaves with water at midday.

What Can I Do About Azalea Gall?

Azalea gall is a common disease of both deciduous and evergreen species.

If you look closely at the blobs or swellings, you will see that they are covered with a white, powdery coating.

This is made up of the spores of the fungus which causes the disease. There is no reliable fungicidal treatment, and affected plants soon lose their vigor.

sketch of azalea gall

The best antidote against azalea gall is to watch for any signs of an attack and then carefully cut off all the infected shoots and burn them immediately.

You can avoid spreading the disease by dipping your knife or secateurs into a disinfectant such as hydrogen peroxide between cuts and by taking care that you do not disturb the spores.

It may be best to discard the whole plant, as it is probably growing in the wrong soil or position.

Do not plant new azaleas in the same place.

What To Do About Yellow Leaves On Azaleas

Yellow leaves on azaleas and other acid-loving plants are a sure sign that the plant needs nitrogen, as well as increased acid.

Mulch the plants heavily with peat or a special acid azalea compost and an application of nitrogen fertilizer.

If they still remain yellow, they should be sprayed with iron chelate according to the manufacturer’s instructions.

While chelates do not acidify the soil, they liberate nutrients in the soil when absorbed by the plant.

Keep on using chelates until the colour of the new leaves improves.

Aluminum sulphate, sulphate of ammonia, and soil sulfur (flowers of sulfur) are acidifying materials than can be applied to the soil to make it more acid.

The application of an organic mulch will do much to improve the general quality of the soil.

Best Mulch For Azaleas

Azaleas and rhododendrons have shallow roots and can suffer badly in dry weather.

A good moisture-retentive mulch for the flower bed is therefore vital. Peat is an obvious choice for such acid-loving plants, but only as long as it’s wet.

When it dries out, it forms a crust that can actually throw off water.

Shredded or pulverized bark is better. It can be bought in bags or in bulk.

Don’t be tempted to buy bargain lots of cheap unbranded bark. It may not have been properly composted and could still contain toxic residues.

One of the cheapest mulches is pine needles, which you can collect for nothing in forests — provided, of course, that you have permission or a permit to do so.

A thick mulch of well-rotted compost is always beneficial.

If Your Azaleas Are Fading Over Time

It could be one or more of three things.

To start with, your garden soil may not suit the plants as well as the acidic compost of the containers in which you bought them. If that’s so, the azaleas won’t push their roots beyond the confines of the compost. And if that happens, the nutrients in the compost will keep the plants going for the first year or two, but after that they’ll starve.

If you think the soil is the problem, there are two solutions.

First, when removing the azalea — or indeed any plant from its container — gently tease the roots out around the edge to encourage them to grow out into the soil.

Be very careful as any damage to the roots will serve to kill the plant.

Second, enrich the soil in which the plant is being placed with acid compost.

Many nurseries sell special acid azalea compost just for this purpose.

Don’t use bone meal — it’s too alkaline for such an acid-loving plant.

Another possible reason for the decline of your plants may be the site. Although azaleas are plants of sheltered, damp woodland, they won’t tolerate a waterlogged, compacted soil. Neither will they do well in a windswept, exposed, dry position.

Make sure the plants are in a cool, sheltered, semi-shaded position. When preparing the site, dig in plenty of bulky organic material, such as compost, peat or bark. This will ensure that the soil retains moisture but does not become waterlogged.

The third reason why your azaleas may be growing badly is the depth at which you’re planting them.

Azaleas and rhododendrons are surface-rooting and do not like being buried deeply.

With a new plant, take care not to set it any deeper than the existing soil mark on its stem.

An ailing plant that’s already in the ground can sometimes be revived by digging it up, dressing the roots with fertiliser and replanting it in a more shallow position.

An important rule to follow is never to dig around azaleas, as this will damage the roots which lie close to the surface.

Remove weeds by hand and keep the surface mulched with a thick layer of compost or pine needles to prevent weed growth and keep in moisture.

How To Propagate Azaleas

There are three ways — by seed, by cuttings, and by layering.

Growing From Seed

Raising azaleas from seed is a lengthy business and, unless you are interested in hybridizing them, worthwhile only with the few, true species.

Propagate Azaleas From Cuttings

Reproduction by cuttings is easy and much quicker.

Take cuttings in late summer when the new wood is semi-ripe: when it can be bent over, but will not snap until it’s been bent almost double.

Cut lengths of healthy shoots about 3 inches (7.62 cm) long and trim away the lower leaves.

As a rooting medium, mix an equal amount by volume of peat moss and river sand.

Spread the mixture in a container to which a more-or-less airtight translucent cover can be fitted — a flowerpot with a plastic bag tied over it will do.

Dip the base of each cutting into a hormone rooting powder, and push it gently into the rooting medium.

Seal the container and stand it in a well-lit spot out of direct sunlight — a greenhouse or shade house would be ideal.

Most azaleas will root within about three months.

Clear or milky plastic bags make good propagating cases for azaleas and for any other small cuttings or seeds.

One way is to up-end a bag over a pot; another is to put the pot or tray right inside the bag and blow the bag up. Support it, if necessary, with wire hoops made from old coat hangers and seal the opening with a freezer tie.

Propagation By Layering

Layering also works well and is the easiest method of all.

Simply select a low-growing shoot or branch and anchor it into the soil with a small wooden peg held down with stones.

Remember where you made the layer, for it may take up to two years to root.

When it has rooted, sever it cleanly from the parent and treat it like a separate plant.

Azalea Varieties

There are many varieties of azaleas which have been hybridized from species indigenous to Asia, China, Japan and the United States of America.

Some of these species are deciduous while others remain evergreen. Generally speaking, the evergreen kinds are able to stand higher temperatures, while the deciduous types will grow under freezing conditions.

Evergreen Azaleas

Azalea indica

This variety has been bred from a group of azaleas which are native to southern Asia, and it grows very well in many areas wherever the right conditions as to soil and humidity are provided.

The flowers are large, sometimes single and sometimes double, and they may be white, pink, rose, mauve, magenta, crimson, salmon or flame in colour.

This particular variety does not like extremes of cold. The ones with white or magenta flowers are the hardiest and grow much more quickly and into larger bushes than the others.

They flower from autumn to early spring.

Kurume azaleas

Dr. Wilson, a renowned plant collector who was passionately fond of azaleas, said, when he discovered these growing in Japan: ‘I think that Kurume azaleas are the loveliest of all azaleas.’

The flowers of this group are smaller than those of the indica group, but they are borne in greater quantities. Shrubs in full bloom are sometimes so covered with flowers that the leaves cannot be seen.

The colours include white, pink, rose, scarlet, salmon and palest mauve. Many of them have flowers which are tinted and shaded.

The Kurumes are hardier than the indica azaleas and less likely to be damaged by severe frost followed by hot days.

Macrantha azaleas are low, spreading shrubs with attractive foliage and flowers which are single or double, pale pink, mauve, salmon, red or white. The flowers open in late autumn and the plants continue producing blooms right through to early spring.

The following are the names of some good Macrantha varieties:

  • Beni-Kirin (blood-red)
  • Fuginishiki (variegated white with lavender lines)
  • Gumpo (white)
  • Izayoi (flesh-pink)
  • Macrantha (double pink)
  • Okinanishiki (orange-red
  • Sakuragata (dark crimson)
  • Wakamatsue (mauve)

Deciduous Azaleas

These start to bloom later than the evergreen species, but the leaves turn to brilliant colours before dropping in the autumn, and they can endure freezing conditions.

If different species are planted, they will produce flowers for a long period.

Among the best known of the deciduous azaleas are the following:

Ghent hybrids.

Nurserymen in Belgium were ardent collectors of azaleas particularly at the beginning of the nineteenth century, and it is to the hybridizing work of some of these nurserymen of Ghent that we owe some of the finest azaleas now cultivated.

These hybrids were the result of crossing an Asiatic strain with an American species.

The autumn tints of their leaves are very striking and the wide, tubular, scented flowers appear at the same time as the new leaves.

This group is outstanding in the variety of colour of the flowers—white, lemon, canary, yellow, orange, copper, bronze, pink, rose, crimson, red, scarlet, mauve and purple.

Mollis azaleas

These come into flower earlier than the Ghent hybrid and are in full bloom before the leaves develop.

The blooms are magnificent in colour, from pale gold to rich orange, yellow, salmon, apricot, pink and deep crimson.

Kaempfer hybrids

These have flowers of striking shades of orange, pink and red.

They are extremely hardy, but the blooms are apt to fade in strong sunlight and they should therefore always be planted in a shady spot in the garden.

How To Prune Azaleas

Please see our article on azalea pruning by clicking the text above.