How to Grow Potted Azaleas? A Detailed Guide to the Latest Cultivation Methods

Azalea is also known as shanzhizhu, yingshanhong, zhaoshanhong, etc. It is an evergreen or semi-evergreen shrub of the genus Rhododendron in the family Ericaceae, with bright red corollas. It is regarded as a famous flowering plant with high ornamental value and is cultivated in parks all over the world. In China, Jiangxi, Anhui and Guizhou have azalea as their provincial flower. Now let us take a look at how to grow potted azaleas!

Growth Habits of Azaleas

Azaleas prefer a cool, humid, well-ventilated semi-shaded environment. They fear both extreme heat and severe cold. The optimum growing temperature is 12°C to 25°C. When the summer temperature exceeds 35°C, new shoots and new leaves grow slowly and the plant enters a semi-dormant state. In summer, protect them from the sun and provide shade; in winter, pay attention to keeping them warm and protecting them from the cold. Avoid direct exposure to the scorching sun; they are suitable for growing under scattered light of low intensity. If the light is too strong, tender leaves are easily scorched, and the edges of both new and old leaves burn, which in severe cases can cause the plant to die. In winter, azaleas grown in the open ground need measures taken to protect them from the cold so they can overwinter safely.

How to Grow Potted Azaleas?

1. Soil: For potted azaleas, choose a loose, humus-rich acidic soil. To plant azaleas, make sure the potting soil is rich in humus and acidic. In addition, ensure the soil is loose, well aerated and well drained. Never use clay or alkaline soil. The pH value of the acidic soil should be controlled between 5.5 and 6.5.

2. Temperature: For potted azaleas, maintain the indoor temperature. There are many varieties of azaleas with different temperature requirements. Most azaleas prefer a warm environment, with a suitable temperature between 15°C and 28°C. In winter, the indoor temperature generally should not be lower than 10°C. When the temperature is too high, azaleas will also stop growing, so in summer it is easy to place them in a cool, ventilated place, and in winter they should be placed indoors; when necessary, the indoor temperature can be increased to prevent cold damage.

3. Watering: Potted azaleas should be watered more during the flowering period and in summer. Azaleas inherently like a humid environment, and during the flowering period from April to June they need even more sufficient moisture, so they should be watered once every evening. In summer, when the climate is hot and dry, since more water evaporates, they should also be watered once a day. In spring and autumn, watering once every 4 days is enough. In winter, azaleas enter dormancy, so the amount of watering can be reduced.

4. Sunlight: Potted azaleas must not be exposed to excessive direct sun. Azaleas cannot be exposed to direct sunlight; when placed in the sun, some shade should be provided to prevent scorching the branches and leaves. However, the specific lighting should also change with the seasons. For example, in spring and autumn, when the sunlight is not strong, about 20% shading is enough; during the flowering period and in summer, 60% shading should be provided.

5. Water quality: For potted azaleas, it is best to use natural water for irrigation. Good natural water includes fish tank water, rainwater, pond water and river water. Usually, some “aged water” can be stored. Aged water means placing water and the azalea in the same temperature place for one or two days, so that the water can reach the same temperature as the soil and also store more nutrients.

6. Fertilizing: Potted azaleas should be given light fertilizer frequently. They like fertilizer but dislike concentrated fertilizer, so do not apply too much at each fertilizing. From February to March, to promote the growth of branches and leaves, a dilute fertilizer mainly of nitrogen and potassium can be applied once every 10 days. From April to June is the flowering period, when phosphorus fertilizer should be the main component and potassium fertilizer supplementary, applied once every 5 days. When the temperature is above 28°C, fertilizing should be stopped. In winter, fertilizing should also be reduced. In daily care, some alum fertilizer water should be applied, or a little ferrous sulfate added to the water, to maintain the acidity of the potting soil.

7. Repotting: Potted azaleas should be repotted in time. When the azalea grows larger, it should be repotted promptly so as not to affect growth. Generally, a 5-inch pot is suitable for a 5-year-old plant, a 6-inch pot for a 7- to 10-year-old plant, and an 8-inch pot for one over 11 years old. When repotting, an appropriate amount of slow-release fertilizer should be added.

8. Pruning: Pruning and shaping is an important measure in daily maintenance and management. It can regulate growth and development, thereby making the plant grow vigorously. In daily pruning, a few diseased branches and weak old branches need to be cut off, and some overly dense branches removed according to the shape of the crown to increase ventilation and light penetration, which is beneficial to plant growth. Azalea gardens must be inspected frequently; if dead or diseased branches are found, they should be removed promptly to reduce the spread of pests and diseases among the azaleas.

9. Bud thinning: Potted azaleas should have their buds thinned in time during the bud stage, so that nutrients are concentrated and supplied to promote large, brightly colored flowers. Pruning branches is generally done in spring and autumn, cutting off crossing branches, overly dense branches, overlapping branches and diseased or weak branches, and promptly removing spent flowers. Shaping generally follows the natural tree form with slight artificial adjustment, at will, shaping according to the tree.

Pest and Disease Control of Azaleas

1. Brown spot disease

[Symptoms] Brown spot disease is a major disease of azaleas. When the disease first appears, small brown spots appear on the leaf surface and gradually develop into irregular large spots. Many small black or grayish-brown dots are produced on the lesions, causing the affected leaves to turn yellow and drop, affecting flowering that year and the development of flower buds the following year. This disease often occurs during the plum rain season when humidity is high.

[Control] Usually pay attention to giving the plant ventilation and light penetration, do not let humidity become too high, and apply more organic fertilizer and mixed nitrogen-phosphorus-potassium fertilizer to enhance the plant's resistance to infection and its growth capacity. If diseased leaves are found, remove them promptly and burn them in a centralized manner. In the early stage of the disease, spray 0.5% Bordeaux mixture or 0.4 Baume degree lime sulfur mixture, and add 4% flour to increase adhesion. Leaf spot disease and black spot disease can also be treated by the same method.

2. Chlorosis

[Symptoms] Iron-deficiency chlorosis often occurs in areas where the soil is somewhat alkaline. When the condition is mild, only delayed greening of the plant appears; when severe, the leaf tissue can all turn yellow and the leaf edges scorch. When the disease occurs, it is most obvious on the leaves at the top shoots of the plant, and it is generally caused by internal iron deficiency.

[Control] Change the iron-deficient nature of the soil and reduce soil alkalinity. Apply more organic fertilizer to improve clayey soil. For iron-deficient plants, directly spray O.2 to 0.3% ferrous sulfate solution. You can also use chopsticks to poke several holes about 15 cm deep in the soil around the plant, slowly inject a 1:30 ferrous sulfate aqueous solution, and fill the holes to increase soil acidity and reduce alkalinity.

3. Lace bug

[Symptoms] The adult lace bug is small and flat, about 4 mm long and black. It is one of the most serious pests harming evergreen azaleas. It often pierces and sucks leaf sap on the back of leaves, causing yellow-white spots to appear on the upper surface of the leaves at the damaged spots, making the leaves drop, weakening the tree's vigor and affecting growth and flowering. Azaleas in greenhouses are extremely prone to this insect.

[Control] Spray 90% trichlorfon technical material at 1000 times dilution, or 40% omethoate emulsifiable concentrate at 1500 times dilution, or 50% fenitrothion emulsion at 1000 to 1500 times dilution for control.

4. Aphids

[Symptoms] Aphids mainly harm the young branches and leaves of azaleas. In mild cases, they can make the leaves lose their green color; in severe cases, they make the leaves curl, become hard and brittle, unable to absorb nutrients, and affect flowering.

[Control] Usually pay special attention to aphids during the overwintering period. After the beginning of winter, spray the plant once with 5-degree lime sulfur mixture to eliminate overwintering eggs, and remove weeds near the flowers to eliminate the source of the insects. During the period of aphid damage, use 40% dimethoate or omethoate plus 1200 times water to make a solution and spray continuously for treatment; 3 to 4 times will be effective.

5. Short-bearded mite

[Symptoms] The short-bearded mite is one of the important pests of azaleas. It often pierces and sucks sap near the main veins on the back of leaves, causing many oily patches to form on the leaf backs and finally causing the leaves to drop.

[Control] In mid-to-late October and early spring in March, spray once each with 0.5 Baume degree lime sulfur mixture or spray 25% insecticidal water agent at 500 times dilution.

6. Red spider mite

[Symptoms] Red spider mites are tiny in size but cause serious harm to azaleas. This kind of pest is most likely to appear on azaleas cultivated in high-rise buildings.

[Control] Carry out manual capture and killing. For chemical insect control, 5-degree lime sulfur mixture can be sprayed, or walnut leaves, oleander leaves and chenopodium each in equal parts can be crushed and soaked to produce a liquid, diluted with water and then sprayed. Spraying 1000 times water-diluted dichlorvos solution to kill them is also a good method.