Analysis of the Causes of Azalea Death or Bud Drop and Countermeasures

The azalea has a graceful tree form and brilliant flowers, and is one of China's ten traditional famous flowers; it is a commonly used flower for landscaping, indoor pot culture, and bonsai making. There are many causes of azalea bud drop or death, mainly:

Soil. Azaleas are suited to growing in acidic sandy loam rich in humus, with strong permeability and a pH value of 5.0 to 6.5, and dislike alkaline soil and clay soil. If the planting site is alkaline or highly clayey with poor aeration, it easily causes poor plant growth, bud drop, and even death.

Fertilization. Too high a fertilization concentration or applying unrotted raw fertilizer will both cause "root burn," leading to bud drop and plant death.

Watering. Azalea roots are extremely fine and fear waterlogging. Too much watering will cause a lack of air in the soil, leading to bud drop, leaf drop, and plant death.

Temperature. The optimum growth temperature for azaleas is 12°C to 25°C; below 5°C or above 35°C, they are both easily damaged.

Pests and diseases. Azaleas have relatively many pests and diseases, mainly leaf gall disease, Stephanitis takeyai, and brevipalpus mites, among others.

Repotting. Not repotting for many years leaves the plant lacking nutrients; improper repotting time, such as repotting in severe winter cold, in spring when flowers are blooming, or during summer high temperatures; improperly prepared potting soil, such as being too alkaline or having poor permeability, will all cause bud drop and plant death.

In response to the above causes, the following technical measures should be taken.

Soil selection. Plant in acidic, well-drained soil rich in humus. If the soil is slightly alkaline, it can be improved: apply 1000 to 1200 kg of rotted farmyard manure (such as pig manure or cow dung) per mu, turn and sun-dry it, and after one year the alkali in the soil will be neutralized by the fertilizer containing large amounts of humic acid. For soil that is heavily clayey and poor in permeability, methods such as mixing in river sand or sawdust, burying green manure, and applying organic fertilizer can be used. For pot culture, the growing medium can be prepared from 45% leaf mold, 45% peat soil, 5% sawdust, and 5% bone meal or rotted cake fertilizer.

Fertilization. Azaleas have green branches and leaves year-round and bloom profusely, consuming large amounts of nutrients, so their fertilizer requirement is also large. But to prevent "root burn," rotted, dilute fertilizer must be applied according to the principle of "light fertilizer applied frequently." In early winter, apply 500 to 700 kg of rotted farmyard manure per mu as a base fertilizer, which can raise soil temperature, benefit azalea growth in winter, and enhance cold resistance for overwintering. In February before spring flowering, apply 1 to 2 times a light fertilizer based mainly on phosphorus fertilizer combined with nitrogen and phosphorus, to promote brilliant flowers and green leaves. After the flowers fade, apply liquid fertilizer based mainly on nitrogen fertilizer 2 to 3 times, with an interval of 10 days each time, to promote the growth of many new branches and tender leaves. During flower bud differentiation, apply rotted cake fertilizer once, and add an appropriate amount of potassium dihydrogen phosphate to promote flower bud differentiation and flower bud formation. To maintain the acidity of the potting soil, water once every 1 to 2 months with a 0.2% ferrous phosphate aqueous solution.

Watering. The azalea's root system is a shallow, fine root mass, fearing both drought and waterlogging; therefore, watering must be moderate, and the planting site must always be kept in a semi-moist state. Water when drought occurs, and drain or irrigate when flooding occurs. During the spring bud and flowering period, the water requirement is large; water thoroughly 2 to 3 times a week to meet the needs of growth and flowering, which can effectively prevent leaf and tender shoot wilting, shortened flowering period, and early flower fading. In summer, temperatures are high, water evaporates quickly, and it is also the period of vigorous branch and leaf growth for azaleas, so the water requirement is even greater; besides watering once each morning and evening, also spray water on the leaf surfaces and around the flower pots to raise air humidity. In autumn and winter, water less, keeping the potting soil slightly moist. At any time, if there is standing water in the planting pot, it must be poured out promptly, and the soil loosened and air-dried. For those suffering particularly severe waterlogging damage, repot and change the soil.

Light. Azaleas are strongly shade-tolerant and suited to growing in a semi-shaded environment; they cannot tolerate strong summer light. Therefore, when choosing a planting site, a relatively shaded, moist place with scattered light, such as under a large tree, is preferable. If potted, in summer the potted flowers should be placed under a large tree to avoid strong light exposure.

Repotting. For potted azaleas, because their root system is well developed, their sprouting ability is strong, their flowering amount is large, and they consume many nutrients, they must be repotted and have their soil changed once every 1 to 2 years. The potting soil is prepared according to the method described in item one above, and the specific repotting time is best after spring flowering or before autumn bud formation. The operation method is: water thoroughly 1 to 2 days before repotting, so that the potting soil swells and loosens; wait until the potting soil is slightly dry, first pat around the flower pot with your hand to separate the potting soil from the pot wall; use a bamboo stick or other sharp object to pry loose the soil in the pot, and gently lift out the plant; remove the soil along the outer edge of the root system and the surface soil, keeping only 1/3 of the old soil; cut off rotten roots, damaged roots, overly long roots, and fine weak roots; change to a pot one size larger, and refill with soil and repot; then water thoroughly once more, and place it in a semi-shaded place for care.