The Rhododendron Indicum is a remarkably beautiful species of Azalea. Originally native to Japan, it is now widely cultivated in China due to its aesthetically pleasing and vibrantly colored flowers, making it highly valued in horticulture.
This semi-evergreen shrub grows to a height of 1-2 meters, has multiple branches with firm twigs initially covered in coarse, reddish-brown hairs that eventually disappear. The flowers, ranging from one to three, bloom at the tip of the branches.
They sport a bright red, sometimes rose-red, broad, funnel-shaped corolla. The flowering period is from May to June.
The Gau Yue Azalea (scientific name: Rhododendron indicum (L.) Sweet) is a semi-evergreen shrub, growing 1-2 meters high. It has multiple branches with firm twigs initially covered in coarse, reddish-brown hairs that eventually disappear.
The leaves are clustered at the branch ends, nearly leather-like, and are narrow-elliptical or inverted-elliptical in shape. The upper side is dark green and glossy, sparsely covered with coarse hairs, while the underside is pale.
The flowers, ranging from one to three, bloom at the tip of the branches. They sport a bright red, sometimes rose-red, broad funnel-shaped corolla, 3-4 cm long, with a diameter of 3.7 cm, and occasionally reaching 6 cm.
The corolla tube is 1.3 cm long, split into 5 parts, and is broadly elliptical. The fruit is an elongated ovate shape, 6-8 mm long, densely covered with reddish-brown, flat, coarse hairs. The flowering period is from May to June.
Originally native to Japan, it is now widely cultivated in China. This species is highly valued in horticulture due to its beautiful, brightly colored flowers.
Originally native to Japan, the Gau Yue Azalea is now widely cultivated in China.
The Gau Yue Azalea is a semi-evergreen shrub, growing 1-2 meters high. It has multiple branches with firm twigs initially covered in coarse, reddish-brown hairs that eventually disappear.
The leaves are clustered at the branch ends, nearly leather-like, and are narrow-elliptical or inverted-elliptical in shape, 1.7-3.2 cm long, rarely 4.5 cm, about 6 mm wide. The tip is blunt, the base is narrow-wedge-shaped, the edges sparsely have fine round serrations.
The upper side is dark green and glossy, sparsely covered with coarse hairs, while the underside is pale.
The midvein is depressed on the upper side and prominent on the underside, the side veins are slightly visible on the underside, and both surfaces have sparse, reddish-brown, coarse hairs. The leaf stalks are 2-4 mm long, covered with reddish-brown, coarse hairs.
The flower buds are ovate, the scales are broad ovate, sharply pointed at the tip, only the outside and the tip have hairs. The flowers, ranging from one to three, bloom at the tip of the branches.
The flower stalks are 0.6-1.2 cm long, covered with white, coarse hairs. The calyx is split into 5 parts, the lobes are elliptical or nearly round, 2-3 mm long, 1.5-2 mm wide, pale green, the outside and the edges are covered with white, soft hairs.
The corolla is bright red, sometimes rose-red, broad funnel-shaped, 3-4 cm long, with a diameter of 3.7 cm, and occasionally reaching 6 cm. The corolla tube is 1.3 cm long, split into 5 parts, and is broadly elliptical, 1.7-2 cm long, 1.6 cm wide, with deep red spots.
The stamens are 5, unequal in length, 1.6-2.2 cm long, shorter than the corolla. The filament is pale red, the middle part below is covered with fine soft hairs, the anther is dark purple-brown, 3 mm long, the base has a fine point.
The ovary is 3.5 mm long, densely covered with shiny brown, coarse hairs, the style is 2.3 cm long, occasionally reaching 4.5 cm, longer than the stamen, hairless.
The fruit is an elongated ovate shape, 6-8 mm long, densely covered with reddish-brown, flat, coarse hairs. The flowering period is from May to June.
Azaleas originate from high-altitude areas and prefer cool, moist climates, but they do not tolerate harsh, hot, and dry weather. Azaleas thrive in acidic soil, rich in humus, loose, moist, and with a pH between 5.5 and 6.5.
Some varieties and horticultural species are highly adaptable, tolerate drought, poor soil, and can grow in soil with a pH between 7 and 8. However, they do not grow well in heavy or poorly-drained soils.
Azaleas have certain light requirements and are not sun-resistant. During summer and autumn, they should be sheltered by deciduous trees or shades to protect from the harsh sun, and the ground should be sprayed frequently with water.
Azaleas typically sprout in spring and autumn, primarily in spring. The most suitable growth temperature is 15-20°C. They bloom from March to May and tolerate pruning.
Pruning should generally be done before May. The new shoots that are produced can form flower buds within the year, but late pruning can affect blooming.
Azaleas require acidic soil for growth and development. Due to the majority of northern soil being more alkaline, the potting soil needs to be prepared using a mixture of rotted pine needle soil and other humus soil.
The root system of azaleas consists of fibrous roots, which have strict requirements for fertilizer concentration and water quality. When fertilizing, it is necessary to follow the principle of timely and appropriate amounts, with frequent application of thin fertilizer.
Prior to blooming in the spring, phosphorus fertilizer can be applied once a month to promote the growth of branches, leaves, and flower buds. After blooming, apply a mixture of nitrogen and phosphorus fertilizer 1-2 times.
During the bud-forming period in September and October, apply phosphorus fertilizer 1-2 times. During the growth and flowering period, more fertilizer and water are needed.
In winter dormancy and slow summer growth, control the amount of fertilizer and water to prevent root rot. Azaleas like a moist and cool environment. The northern climate is dry, so timely watering and spraying are necessary to maintain high air humidity.
The best water for watering is alum fertilizer water and rainwater. If you use common water, add a small amount of ferrous sulfate and vinegar. You can also cut watermelon or tomatoes into small pieces and apply them to the soil, which can also improve the soil quality and the quality of the flowers.
To accelerate the full bloom of the plant, azaleas often promote new branches through pinching. For crowded flowers that affect the shape of the flower, you can thin the buds early.
This not only makes the flowers larger and brighter that year, but it also benefits the growth and blooming of the plant in the following year. Azaleas have strong sprouting power.
Branches severely affect the growth and development of the plant, reducing its ornamental and commercial value, so pruning is needed to adjust. Pruning is usually done after the flowers fade in spring and in autumn.
Cut off dead branches, slanting branches, excessively long branches, branches with pests and diseases, and some crossing branches to avoid nutrient consumption and make the entire plant bloom abundantly.
Azaleas undergo flower bud differentiation in autumn. Through refrigeration and heating treatments, the blooming period can be artificially controlled.
To make azaleas bloom early, they can be moved to a greenhouse for cultivation, controlling the temperature at 20-25°C, and frequently spraying water on the branches and leaves to maintain a relative humidity of over 80%.
In this way, they can bloom after a month and a half. To delay the blooming of azaleas, the azalea with formed flower buds can be kept at a low temperature, maintaining a temperature of 2-4°C, watering when the pot is dry, moving it outside in summer and autumn, and it can bloom after 2 weeks.
The cutting propagation is the most commonly used method in the cultivation of azaleas. Usually, in May and June, semi-lignified new branches that are healthy and about 5-8 cm long are cut.
The leaves at the lower part are removed, leaving 2-3 leaves at the top for the cutting. It is best to dip the base of the cutting in a solution of indole butyric acid or ABT rooting powder, then insert it into loose, breathable, humus-rich acidic soil.
Maintain a temperature of 20-25℃, provide shade, and frequently mist to keep it moist, which promotes the sprouting of new roots.
Soft branch propagation is used for grafting difficult-to-survive, valuable varieties like the West Azalea.
First, cut about 3-4 cm of the soft branch to serve as the scion, shave the base into a wedge shape with a sharp knife, use the Rhododendron as the rootstock, adopt soft branch grafting, then place it under a shaded shed, bind it with plastic film, and cover the scion and rootstock together with a plastic bag to retain moisture.
Before an outbreak, especially during the budding and leaf expansion period, spray 1:1:200 Bordeaux mixture. Diseased leaves should be promptly removed. Before budding, spray 0.3-0.5% Bome Degree Stone Sulfur Compound or 1:1:200 Bordeaux mixture 2-3 times, usually once every 7-10 days.
After an outbreak, spray 65-80% Daisen manganese zinc 500 times liquid or 0.3-0.5% Bome Degree Stone Sulfur Compound 3-4 times, once every 7-10 days.
Leaf spot and brown spot diseases can be controlled by spraying 70% methyl tobuzin 1000 times liquid, 20% rust ning 4000 times liquid, or 50% Daisen manganese zinc 500 times liquid from May to August.
Spray once every 10 days, for a total of 7-8 times. To prevent leaf yellowing, additional ferrous sulfate can be applied.
Affected tender branches and leaf tips are covered with a dense white or pink mite layer, sometimes leaf mites occur, often caused by aphid bites.
The control methods include: while removing diseased leaves, spray a solution containing copper sulfate; spraying oxidized leco emulsion or placing furan directly in the pot can prevent aphids and other piercing mouthpart pests.
This species is similar to Rhododendron simsii Planch., but can be distinguished by its five stamens and leaves with fine round-toothed serrations.
The azalea is lush and colorful with strong sprouting ability, resistance to pruning, and unique root shapes, making it an excellent bonsai material.
It is most suitable for planting in clusters along the edge of forests, streams, ponds, and rocks. It can also be scattered under sparse forests and is a good material for flower hedges. It can be pruned into various shapes.
Even when not in bloom, its deep green leaves make it suitable for planting in gardens as low walls or barriers. During the flowering season, azaleas always give a lively and bustling feel.
Peggie was once a high school mathematics teacher, but she set aside her chalkboard and textbooks to follow her lifelong passion for flowers. After years of dedication and learning, she not only established a thriving flower shop but also founded this blog, “Flowers Library”. If you have any questions or wish to learn more about flowers, feel free to contact Peggie.
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