First, do not be alarmed. From my perspective, the most common reason for a single leaf—typically the oldest, lowest one—to turn yellow is simply the end of its natural life cycle. I am a living organism, and my resources are finite. As I grow new leaves and roots from my crown, I must strategically reallocate energy and nutrients. The older leaves have served me well, but they become less efficient over time. By allowing one to yellow, wither, and eventually fall, I can salvage valuable materials like nitrogen and redirect them to support new growth, such as a fresh leaf or a budding flower spike. This is a sign of a healthy renewal process, not decay.
Your watering habits are the most frequent source of stress in my life, manifesting in yellow leaves in two opposite ways. Overwatering is a silent killer. When my potting medium remains soggy for days, it suffocates my roots. They are not like the roots of other plants; they are aerial roots designed to breathe. When waterlogged, they rot, turning brown and mushy. With a compromised root system, I cannot uptake water or nutrients, and the signal of this distress is sent upwards as yellow, limp, and often wrinkled leaves. Conversely, Underwatering also causes yellowing, but the presentation is different. My leaves will become yellow, but they will also feel leathery, thin, and severely wrinkled because they are literally dehydrating and starving. It is a desperate cry for the sustenance I need to function.
While I am not a heavy feeder, I still require a balanced diet to maintain my vibrant green foliage and produce spectacular blooms. If I am grown in a bark-based medium, which is common, I rely on you for all my nutrition. A lack of essential nutrients, particularly nitrogen, which is crucial for chlorophyll production and leaf growth, will cause a general, overall yellowing of my leaves. This chlorosis starts with the older leaves but can spread if the deficiency persists. It is a slow starvation, a gradual fading of my vitality because I lack the basic building blocks to sustain myself.
Light is my source of energy, but the correct amount is a delicate balance. Too much light will cause a stress response. My leaves may develop a reddish or purplish tinge before turning a pale yellow or even white in severe cases. They might also show sunburn spots—black or brown patches where the leaf tissue has literally been scorched. This is me getting a severe sunburn. On the other hand, too little light also causes problems. While the leaves may remain dark green, they often become weak and floppy, and the lack of energy can contribute to a general yellowing and prevent me from flowering. I need bright, indirect light to photosynthesize efficiently without being damaged.
Finally, consider my pot. If I have been in the same medium for two years or more, it has likely broken down. This decomposed medium retains far too much water, leading to the root rot described earlier, and becomes acidic, which can harm my roots. Furthermore, if my roots have completely filled the pot, I become pot-bound. This extreme crowding stresses my entire system, making it difficult to uptake water and nutrients effectively, which again can lead to yellowing leaves. A timely repotting into a fresh, airy medium gives my roots the space and environment they need to thrive, supporting healthy foliage above.
