Reasons for Yellowing Orchid Leaves and How to Fix Them

      Mid-spring is precisely the period when orchid new shoots grow rapidly. It is no exaggeration to say that they change every single day; if you don't believe it, just observe every morning and you will surely be moved. Look three times a day, and you never tire of it; every time you gain something. Watching orchid new shoots emerge from the soil one after another, the joy in your heart is beyond words, and a sense of achievement and pride instantly surges up. Those pure white, milky white, light purple, deep purple, bright red, water red, mercury red, yellow-white, flesh-colored, and emerald green new shoots in dazzling profusion truly present a scene of a hundred shoots vying in spring, each showing its elegance, making one linger and delight in it. While admiring the beautiful new shoots, there is also a sight that spoils the view, namely yellow leaves. Many new orchid growers tend to worry greatly about this, so I will share some of my views here, hoping to be of help and inspiration to new orchid friends.

        I. Overview of Yellow Leaves from Metabolism 

       The lifespan of an orchid plant is generally about 5 years, with very few able to grow to 7 years. As the years increase and new seedlings multiply, the "ancestral-generation grass" will choose the appropriate time to "leave." As for the timing of this "leaving," 80% choose mid-spring and 20% choose mid-autumn; this is also the "legal" day for the alternation of old and new in orchids. Seeing the "grandchild-generation grass" grow vigorously is exactly what the "ancestral-generation grass" exchanges for by retiring early and "leaving its post." Therefore, skilled orchid growers often, by exercising proper judgment, adopt the method of forced division to make the soon-to-retire "ancestral-generation grass" serve another half year to a year or longer. Of course, this can only be done on the premise that the pseudobulbs are plump and sturdy and meet certain requirements. Mr. Zhou of Shengzhou, Zhejiang, can make qualified "ancestral-generation grass" produce about two more generations of seedlings, which shows his superb orchid-growing skill.

       1. Yellow leaves caused by metabolism 

Yellow leaves on old grass are an instinctive measure taken to nurture the sprouting of the next generation of new shoots, mainly by cutting off their nutrient-absorbing function to ensure the healthy growth and development of the new shoots. The period when this occurs in large numbers is spring and autumn, when new shoots sprout. The pattern of occurrence is that yellowing starts from the lowest leaves of the oldest plant, then spreads from the leaf tip toward the petiole until the entire leaf is affected. Most appear earth-yellow; over time they turn brownish-yellow, and if not pruned artificially for even longer, they become brittle and easy to break at the ring. Whether or not there is a ring, old orchid leaves like these will successively wither downward and end their entire course. This cyclical manifestation of metabolism is something veteran orchid growers can handle with ease. It is mainly beginners who do not understand it and become nervous, always suspecting that the orchid has caught some disease.

       2. Yellow leaves caused by water damage 

       As temperatures rise in late spring and early summer, new grass that did not fully grow last year will accelerate its growth at this time. At this time some orchid growers like to mist to increase humidity; if it is not dried promptly, "heart rot" can occur. The pattern of yellow leaves from water damage is that it starts from the central leaves of the growing new grass, and rarely starts from the central leaves of old grass. 

       3. Yellow leaves caused by disease 

       Yellow leaves caused by disease generally appear yellow-brown and are mostly invasive diseases caused by harmful fungi and bacteria. The pattern of this type of onset also starts from the lowest leaves and spreads from the leaf tip toward the petiole; the difference is that both old leaves and tender leaves may be affected. Do a good job of environmental sanitation in the orchid room and apply preventive chemicals regularly. Adding beneficial microbial bacteria in the orchid room can effectively prevent the occurrence of infectious yellow leaves. 

      4. Yellow leaves caused by element deficiency 

       This type can be classified as physiological yellow leaves. It occurs from time to time during the growth period of new leaves and is mostly caused by the lack of some trace element, known as "chlorosis." The pattern of onset is that it starts from the middle part of the new leaf; the chlorotic area is rather yellow, with strong color contrast. Symptoms: the chlorotic area is smooth and glossy and can be seen through the back of the leaf, and as the leaf gradually matures it returns to normal leaf color. In the early stage of onset, many orchid growers mistakenly think it is "Bailasi." In fact, it is fundamentally different from "Bailasi."

        III. Strengthen effective management of fertilizer, water, and chemicals 

        In summary, several kinds of yellow leaves are caused by different reasons. Now let me discuss the effects of fertilizer and water on yellow leaves: 

       1. When the ancestral-generation grass is being used alone to promote shoots, fertilization must be light or not applied at all; after the new seedlings grow roots, apply light fertilizer appropriately. Some orchid growers have conducted experiments: when promoting shoots on ancestral-generation grass, managing fertilizer the same as for strong grass resulted in accelerated yellowing and collapse of the ancestral-generation grass, which indirectly affected the rejuvenation of the new shoots produced. 

      2. Increase humidity through other means to reduce misting for humidity, so as to prevent water damage and the appearance of central yellow leaves. 

      3. To prevent disease, chemicals must be used alternately to achieve the best preventive effect and prevent the orchids from developing chemical resistance. 

      4. Give priority to organic fertilizers, with inorganic fertilizers or bacterial fertilizers as supplements; hormones should be strictly controlled and not abused to reduce the occurrence of deficiency symptoms.