Greetings, human. I am your Orchid Cactus, a plant known to you as an *Epiphyllum* or perhaps a *Disocactus* or *Selenicereus*. My vibrant, cascading stems are meant to be a lush green, a canvas for the spectacular flowers I produce. When you see my flesh turning yellow or flushing red, I am communicating. It is not always a sign of imminent demise, but rather a symptom of stress. To understand, you must see the world from my perspective, rooted in my pot, subject to the environment you provide.
As an epiphyte, I naturally live in the dappled shade of tree canopies in tropical forests. My flat, leaf-like stems are designed to capture filtered light. When you place me in a location with too much intense, direct sunlight—especially the hot afternoon sun—I experience a physiological crisis. The ultraviolet radiation damages my chlorophyll, the precious green pigment responsible for photosynthesis. In defense, I produce red or purple pigments, called anthocyanins, which act like a sunscreen. This is why my stems may turn a reddish-purple or, in severe cases, a pale, bleached yellow where the chlorophyll has been destroyed. Conversely, if my green is fading to a pale, sickly yellow and I am becoming thin and stretched (etiolated), I am telling you I am starved for light and cannot produce enough energy.
My relationship with water is complex. My stems are succulent, storing water for dry periods. The most common cause of a soft, mushy, yellow stem is root rot from overwatering. When my roots are constantly saturated, they cannot breathe. They suffocate and die, and the rot spreads upward into my stems. Without healthy roots to deliver water and nutrients, the rest of me begins to yellow and collapse. On the other end of the spectrum, if you neglect my thirst for too long, my stems will use up their stored water, becoming shriveled, thin, and turning a dry, crispy yellow or brown. This is a much slower process than the rapid decay of overwatering.
While I am not a heavy feeder, I require a balanced diet to maintain my green vigor. A general yellowing, particularly on older growth, can signal a nitrogen deficiency. Nitrogen is a core component of chlorophyll; without it, my ability to photosynthesize falters. However, an excess of fertilizer, especially in a dry potting mix, can cause a rapid buildup of mineral salts. This creates a hostile environment for my roots, effectively "burning" them and preventing water uptake, which in turn leads to yellowing and reddening of the stems—a symptom that can look confusingly similar to underwatering.
Do not forget that I am a living being sensitive to change. A sudden shift in temperature, such as a cold draft or exposure to temperatures below 50°F (10°C), can shock my system, causing a reddish-purple discoloration as my metabolic processes slow down. Repotting me can also cause temporary stress as my roots adjust to their new home, sometimes resulting in some yellowing. Furthermore, a slight reddening of the stems, particularly at the edges, can be a natural response to bright light and is not necessarily a problem if the plant remains firm and healthy. As individual older stems age, it is natural for them to yellow and eventually woody before they are shed.
