Azalea - Ericaceae - How to care for and grow Azalea plants



Azaleas (synonym of Rhododendron) are splendid plants spread all over the world and very appreciated for their splendid blooms.






: Angiosperms


: Eudicotyledons


: Roside











: see the paragraph on "Main species"


Plants commonly known as azaleas are actually the genus Rhododendronand belong to the family of Ericaceae.

Azaleas are native plants of wooded and humid high mountain areas, where they spontaneously vegetate next to streams and in shady positions, at altitudes even higher than 4000 m; they come from Asia (Nepal, China, Japan, North Korea, Vietnam) from North America (Florida) and from Northern Europe. In Italy they were introduced in 1800 by the English woolmen in the Biella area and in this area they found the climatic and pedological conditions (acid soils) in their favor; currently the main producers are located along Lake Maggiore and in Pontremoli (province of Massa Carrara - Tuscany).

The genre Rhododendron it was established by the botanist Andrea Cesalpino in 1580. Later, in 1780, Linnaeus created the genreAzalea, but after a few years he realized that between the two genres there were no substantial differences so he included the genre Azalea in the genre Rhododendron and this distinction currently exists only commercially.

The botanical classification of this species is very complex, so much so that the Royal Horticoltural Societyof London annually publishes revisions, additions and abolitions.

However, there are some different between rhododendron and azalea:

  • rhododendrons are specimens of considerable size, up to 4 m tall, with large persistent leaves, even if there are small specimens such as the Rhododendron hirsutum and the Rhododendron ferrugineum, particularly suitable for rock gardens with flowers carried by robust petioles with consistent and fleshy petals and provided with ribs on the outside and with 10 stamens;
  • azaleas are small in size, suitable for pot cultivation and generally lose their leaves in winter; moreover, their flowers have only 5 stamens.

In general, azaleas are shrubs with oval, hairy and leathery leaves.

The flower has a calyx formed by 5 sepals and a corolla with 5 petals, which in the double forms can be numerous; the flowers are found at the axil of the leaves or gathered in corymb inflorescences.

The fruit of the azaleas is a brown capsule that contains many tiny seeds.


The main distinction between Rhododendron or azalea is made between deciduous and persistent leaved plants.

Among those a deciduous leaf remember:

  • Rhododendron luteum

    , the only one of European origin (spontaneous in Poland), with yellow flowers;
  • Rhododendron japonicum

    , originally from Japan with yellow flowers;
  • Soft rhododendron

    , coming from China, with yellow flowers.

It also includes some rhododendrons originally from Florida, used in genetic improvement work to give rise to different cultivars. The most important species are: Rhododendron canescens pink and white; Rhododendron alabamense with yellow flowers, Rhododendron austrinum is Rhododendronbakeri with yellow flowers. We also remember the group of hybrids such as i ghent, the hybrids of mollis and i knapp-Hill.

Among those a persistent leaf are widespread:

  • Rhododendron indicum, of Japan, which has two types of leaves: the spring ones which fall in autumn and the summer ones, small and leathery, which fall in the following spring;
  • Rhododendron simsiiof China, with pink flowers
  • Rhododendron korume, originally from Japan.


During the spring-summer period the azalea can also live well outdoors in shady and humid places; in the autumn-winter period, during which it blooms abundantly, it can be placed inside the house, as long as it is well away from heat sources and direct sunlight.

The optimal growth temperature ranges from 8 ° C to 16 ° C.

It is important to ensure that your azaleas have good air exchange.


The azalea must be watered frequently with non-calcareous water (possibly rainwater) in order to keep the substratum always humid; for this reason it is useful to keep the pots above the layers of gravel moistened and to nebulize the foliage frequently (for this purpose you can use water mixed with a product based on Thiophanate metyl, which avoids yellowing of the leaves due to limestone).


The azalea grown in pots needs soft and well-ventilated substrates (excellent ones composed in equal parts of peat, perlite, pine needles and moorland) and above all physiologically acid, free of limestone, as it is a very sensitive plant to the presence of calcium and magnesium in the soil and irrigation water, to which it reacts with the yellowing and fall of the leaves.

The plant is repotted when the roots have occupied all the space available to them.


The azalea does not have high nutritional needs, however it is good to give it liquid fertilizers with the watering water about every 15 days.

It is advisable to choose physiologically acid fertilizers, such as urea and sulphates, to be administered in the period from April to September, when the azalea plants are kept outdoors, while they stop fertilizing when the azaleas are brought inside.

At the beginning of spring the azaleas are mainly given nitrogen (urea and ammonia nitrogen) to favor the vegetative recovery.

In summer, potassium is favored, which stimulates flowering (as long as it is not in the form of potassium chloride because chlorine damages it).

At the end of September, slow-acting fertilizers (Osmocote and Nitrophoska) can be administered.

During the other periods the fertilizations are suspended.


Azalea is a plant that gives extraordinary blooms, with very colorful flowers that bloom during the winter, around Christmas.

After flowering, dried flowers must be eliminated promptly to avoid the formation of seeds that would impoverish the plant.

Be very careful not to remove the flower buds.


The rhododendron in mid-spring can be pruned lightly by shortening the branches that have become too long by cutting them immediately above a large hexane bud (with an oblique cut) or a tuft of leaves both to restore vigor to the plant and to give it a more orderly appearance.

Make sure that the tool you use for cutting is clean and disinfected (preferably with a flame) to avoid infecting the tissues.


The azalea multiplies by seed only in genetic improvement and to obtain rootstocks.The most common method of propagation is by cutting.


In the period from July to September, herbaceous or semi-woody shoots of azaleas about 10 cm long are taken, which are rooted in a small box containing peat and perlite.

The cuttings should be cut immediately under the node so that some leaves remain and eliminating the lower ones. Also choose them from azalerobusts and in good health.

It is recommended to cut obliquely as this allows for a greater surface for rooting and avoids the accumulation of water on this surface. Use a razor blade or a sharp knife to avoid fraying of the fabrics. Make sure that the tool you use for cutting is clean and disinfected (preferably over a flame) to avoid infecting the tissues and disinfect it at each cut.

Immerse the cut part in a rhizogenic powder mixed with a good broad spectrum fungicide (available from a good nurseryman) to favor rooting and prevent any fungal attacks. Then arrange the cuttings in a compote formed in equal parts of peat and perlite. Make a hole with a pencil and place it at a depth of 1.5-2 cm. Then take care to gently compact the soil.

The box or pot that contains the azalea cuttings is preferable to cover them with a transparent plastic sheet (or a hooded bag) and place it in semi-dim light and at a temperature around 20 ° C taking care to always keep the soil slightly humid (always water without wetting the rooting plant with water at room temperature). Remove the plastic every day, check the soil moisture and eliminate condensation from the plastic.

After about a month, the cuttings will have developed a very thin and fragile root system, so they will be carefully potted into 8 cm diameter pots containing a substrate of peat, pine needles and land moor.

About 20 days later the flower bud is formed which must be removed immediately and at the same time a topping is carried out in order to set up a harmonious scaffolding of the plant. The suckers (shoots which form at the base of the azaleas and which do not bear flowers) are also regularly removed.

After two months it is repotted in 15 cm diameter pots, always on a soft and porous substrate.

Pruning is then carried out annually, cutting the shoots just above a bud in order to give a rounded shape to the crown of the azalea.


The diseases that most frequently affect azaleas in apartments are mainly physiopathies.

Withered, discolored leaves and flowers

This symptomatology denotes a lack of water.
Remedies: action is taken immediately by completely immersing the jar in water until no more air bubbles form and then it leaves to drain.

Appearance of brown spots on leaves and flowers

brown spots form when the ambient temperature is too high, accompanied by low air humidity.
Remedies: it is advisable to ventilate and nebulize the environment (if it is possible to move the azalea outdoors every evening, as long as it is sheltered from frost).

Leaves that lose their luster and wither

Over time, this disease affects all the aerial parts of the plant and over time also the roots. It is a mushroom la Phytopthora cactorum, and it is a serious illness.

Remedies: the affected parts must be eliminated immediately and two to three chemical treatments are carried out with copper-based products.

Leaves that begin to turn yellow, appear mottled with yellow and brown

Following these manifestations, the leaves curl up, take on an almost powdery appearance and fall off. By observing carefully, you can also notice thin cobwebs especially on the underside of the leaves. With this symptomatology we are very likely in the presence of an attack of red spider, a very annoying and harmful mite.

Remedies: increase the frequency of nebulizations to the foliage (the lack of humidity favors their proliferation) and possibly, only in the case of particularly serious infestations, use a specific insecticide. If the plant is particularly large, you can also try cleaning the leaves to mechanically eliminate the parasite using a wet and soapy cotton ball. After that the plant must be rinsed very well to remove all the soap.


The azalea was already known in ancient times, as the flowers of many species, especially Asian ones, are particularly rich in nectar even if some are poisonous. This fact was already known in ancient times, so much so that Pliny himself reports of an intoxication of the soldiers of the Roman army, during the Asian campaign, caused by honey of poisonous species.Moreover, many rhododendrons contain glycosides with antiseptic and antirheumatic properties and substances that are used as stabilizers in color photo printing.


See: «Azalea - The language of flowers and plants».

Video: How To Propagate Azaleas From Cuttings. full explanation

Previous Article

Information About Prayer Plants

Next Article

Tips For Winterizing Potted Strawberry Plants