Rhododendron: China's Top Ten Famous Flowers - Growing Methods, Precautions, and Blooming Frequency

Rhododendron, also known as yingshanhong (mountain red) or shanshiliu (mountain pomegranate), is an evergreen or semi-evergreen shrub. It is one of China's top ten famous flowers, and among all ornamental flowering plants, it can be said to combine beautiful flowers and foliage, suitable for both ground planting and container growing. The most widely used of all is the rhododendron. So what are the growing methods and precautions for rhododendron? When does it bloom? How many times a year does it bloom?

Introduction to Rhododendron

Legend has it that in ancient times there was a cuckoo bird that cried mournfully day and night until it coughed blood, which stained the flowers all over the mountains red, hence the name. Rhododendron generally blooms in spring, with 2-6 flowers per cluster, funnel-shaped corollas, in colors including red, light red, apricot red, snow blue, and white, with lush and brilliant blooms. It grows in mountain open thickets or under pine forests at altitudes of 500-1200 (-2500) m, and is a typical acid-soil indicator plant of central-southern and southwestern China.

The entire plant of this species is used medicinally: it promotes the flow of qi and blood circulation, tonifies deficiency, and treats internal injury cough, kidney-deficiency deafness, irregular menstruation, rheumatism, and other diseases. Because of its bright red corolla, it is a famous flowering plant with high ornamental value, and is cultivated in parks around the world. In China, Jiangxi, Anhui, and Guizhou have adopted rhododendron as their provincial flower, and as many as seven or eight cities including Changsha, Wuxi, Jiujiang, Zhenjiang, Dali, Jiaxing, and Ganzhou have designated it as their city flower. In May 1985, rhododendron was rated sixth among China's top ten famous flowers.

Growing Methods for Rhododendron

1. Environmental conditions: When cultivating rhododendron, it is best to have both indoor and outdoor environments. The indoor environment is used in winter. The outdoor site is used in summer and autumn, preferably with a mud ground, avoiding cement ground. The site should be spacious, ventilated, and shaded, with a shade shed built above, covered with reed curtains or making use of natural forest shade, with a light transmittance of about 30% being suitable, and absolutely avoiding afternoon sun exposure.

2. Pot soil requirements: Rhododendron prefers loose, highly permeable, well-drained, humus-rich acidic soil with a pH of 5.0-6.0. If clay or alkaline soil is used, hardly one in a hundred will survive. Especially for summer rhododendrons and Western rhododendrons, mountain soil is essential. The mountain soil must also be improved, and currently three types of prepared growing soil are commonly used.

3. Flower pot selection: For cultivating rhododendron, generally two types of pots are used: clay pots and purple clay pots. Clay pots have good air and water permeability, and production units all use these pots for cultivation. Finished rhododendrons, especially those already shaped, for indoor and outdoor display, are generally planted in beautiful and elegant purple clay pots; purple clay pots have a fine texture, rich colors, and beautiful shapes, which can double the ornamental value.

4. Improving water quality: For watering rhododendron, rainwater is best, followed by river water or pond water. If tap water is used, it should be stored for 1-2 days to let the chlorine evaporate before use. When using it, add 0.2% ferrous sulfate, and water once every 7-10 days during the growing season; regular use ensures the soil remains acidic.

5. Fertilizer and water management: Rhododendron prefers shade and moisture, and should not be too dry. During the flowering period, even more water is needed. In winter, rhododendron has entered its dormant period and does not need much water; generally water once every 4-5 days, preferably around noon on clear and warm days;

6. Outdoor shading: From before being moved outdoors until before flowering, it should receive more sunlight; during the flowering period, short periods of shading are needed at noon, with a light transmittance of 60%.

7. Shaping and pruning: Rhododendron grows relatively slowly, and is generally allowed to grow naturally; shaping is only done after flowering, cutting off leggy branches, diseased and weak branches, deformed branches, and damaged branches.

8. Disease and pest control: For the azalea lace bug (also known as the crowned lace bug), spray 40% dimethoate 1500x solution during the infestation period, once every 7 days, for 3 consecutive times. For the terminal bud leaf roller, control mainly relies on manual capture and killing; larvae or pupae can also be sprayed with 40% dimethoate emulsifiable concentrate 2000x solution or dichlorvos 1500x solution.

Precautions for Growing Rhododendron

1. Rhododendron's roots are as fine as hair strands, with few thick main roots; it fears both dryness and waterlogging, and especially fears heavy fertilizer. If watered too much, the roots soak in water; if too dry, the branches and leaves shrink and the leaves fall off, posing a great threat to the plant; as for applying heavy fertilizer, it can endanger its life.

2. After the flowers fade, the spent flowers must be cut off to avoid seed production consuming nutrients; after new branches sprout, appropriately thin the branches, deciding what to keep or remove based on the plant's growth vigor.

3. Rhododendron is best planted in clay pots, because clay pots absorb water and breathe, which benefits root growth and development and makes branches and leaves lush.

4. The placement of potted rhododendron is particular; it should generally be placed on a southeast-facing balcony, and it must be ventilated, with as little moving as possible. Without ventilation, it is prone to black spot disease and massive leaf drop.

5. Rhododendron's light requirements should also be moderate; avoid direct light in summer.

6. Timely thin buds and leaves, removing part of the overly numerous and dense buds and leaves to allow air circulation and concentrate nutrients into the buds. After the buds form, increase nutrition and apply an appropriate amount of extra phosphorus and potassium fertilizer, otherwise the buds will turn into leaf buds.

7. The main reasons for rhododendron leaf drop and failure to bloom are: too strong direct sunlight in summer, frost damage from severe cold, too much watering, too concentrated fertilizer, being kept indoors for too long, being placed in unventilated or dark and damp places, exposure to acid rain, etc., so these situations should be avoided during care.

8. Repotting and changing soil does not need to be done every year, generally once every 2 to 3 years, with as little damage to the roots as possible; the time should be after the flowers fade or in autumn, and at the same time spray thiophanate to prevent disease.

9. The main pests of rhododendron are red spiders, aphids, etc., which can be sprayed with fenvalerate, etc., with good results; if they do not die after three days, spray again.

10. Rhododendron propagation is mainly by cuttings. Around the time of Grain in Ear (Mangzhong), select new branches 5 cm to 10 cm long, cut them at the branching point, strip the lower leaves, keep 3 to 4 top leaves, insert 1/3 of the branch into the soil, spray enough water, and cover with plastic film. Strengthen management at ordinary times, and transplant after one year.

When Does Rhododendron Bloom

1. Rhododendron blooming time

Different rhododendron varieties and different care regions mean different blooming times. In most cases, the flowering period is between April and June; if there is sufficient light, the flowers can last for one month. If cared for improperly, they can only bloom for 1-2 weeks.

In addition, spring rhododendrons bloom in April, summer rhododendrons bloom in May-June, and other varieties fall between spring and summer. As for regions, rhododendrons cultivated in greenhouses in the north can bloom in January-February, those in open fields bloom in March-May, and in high-altitude environments they bloom in July-August.

2. How many times does rhododendron bloom a year

Rhododendron generally has three flowering periods: spring rhododendron blooms generally between April and May, and always blooms first before sending out new leaves; summer rhododendron blooms in May-June, and sends out new leaves first before blooming; spring-summer rhododendrons bloom between the two, with flowers and leaves sprouting almost simultaneously. In general, each variety of rhododendron blooms only once a year; keeping a hybrid variety at home can provide alternating blooms. However, some places have now even bred rhododendrons that bloom in all four seasons.

Brief Introduction to Rhododendron Lines and Blooming Periods

Rhododendrons are divided into the “five major” lines: the spring rhododendron line, the summer rhododendron line, the Western rhododendron line, the Eastern rhododendron line, and the alpine rhododendron line.

1. Spring rhododendron blooms in April: refers to varieties that bloom first and then sprout, blooming in mid-to-late April and early May; the so-called spring rhododendron was first mainly introduced from Japan to Shanghai for cultivation by Mr. Shen Yuanru in the 1920s-1930s, while local flower farmers formed unique domestic varieties through selection and hybridization of the original species. Because it blooms in spring, it was named spring rhododendron, and this name has continued to this day.

2. Summer rhododendron blooms in May: it first grows branches and leaves in spring, then blooms in early May-June, hence called summer rhododendron. The main parents of summer rhododendron are said to be Rhododendron indicum and Rhododendron mayense.

3. Eastern rhododendron blooms in spring: it is a variety of Japan's Rhododendron obtusum and its many hybrid descendants, introduced from Japan, and called Eastern rhododendron to correspond with Western rhododendron.

4. Western rhododendron can bloom as early as New Year's Day and Spring Festival: (1) The plant is low and semi-spreading, grows slowly, and is evergreen; (2) The branches are thick, short, and strong; current-year branches are green or red, related to flower color; red branches mostly bear red flowers, while green branches bear white, pink-white, and peach-red flowers; (3) The leaves are thick and deep green, clustered at the branch tips; leaf size falls between the large-leaved hairy spring rhododendron and the Eastern rhododendron, with few hairs on the leaf surface and many variations in shape. The flower color can be roughly known from the color change at the leaf tip: if the tip is white and transparent, the flower color is white or another light color; if the tip is red, the flower is red.

5. Alpine rhododendron blooms in April-May: it is an evergreen shrub or small tree of the family Ericaceae. The flower types are mainly double-layered and double-petaled, with a few single-petaled ones, and the flowering period is about 1 month. Flower colors include white, pink, light red, peach red, yellow, etc. It generally grows in mountain wilds at altitudes of 600-800 m, has strong adaptability, and after artificial domestication and cultivation, is expected to become an evergreen ornamental plant in garden green spaces.

The Symbolism of Rhododendron

Rhododendron is an auspicious and beautiful flower in our country; during festivals and celebrations, it is often used to decorate public places, expressing the meaning of praising the motherland's prosperity. Giving rhododendron to international friends symbolizes our country's long culture and flourishing civilization, and wishes for lasting friendship. Giving rhododendron to compatriots overseas symbolizes the care and longing of the motherland's loved ones for those abroad. Giving rhododendron to friends blesses them with a bright future. People who travel far away give rhododendron to each other to express homesickness and nostalgia.