From our perspective as Dendrobium orchids, our roots are our lifeline. We are epiphytes, meaning we naturally grow on trees and other surfaces in the wild, not in soil. Our thick, velamen-covered roots are designed to quickly absorb water and nutrients from rainfall and humid air, and to anchor us to our host. The velamen acts like a sponge, but it also requires a cycle of wetting and drying to function properly. When this cycle is disrupted, and our roots are constantly suffocated in a soggy environment, they cannot breathe. This is the primary precursor to the catastrophic condition you call root rot.
The fundamental cause of our roots rotting is not just water itself, but the constant lack of air around them. When planted in a dense, water-retentive medium that never dries out, or when you are too generous with watering, the air pockets in the potting mix are permanently filled with water. Our roots are living organs that require oxygen for respiration. Deprived of oxygen, the root cells suffocate and die. Once dead, they become soft and mushy, creating the perfect entry point for opportunistic pathogens. While fungal and bacterial infections are often the immediate cause of the tissue decay, they are secondary; the primary insult was the anaerobic environment you provided.
Several other factors from your care routine can create this hostile, suffocating environment. A pot that is too large for our root system holds moisture for far too long, as our small mass of roots cannot absorb the vast amount of water in the excess medium. A pot without adequate drainage holes traps water at the bottom, drowning our lowest roots. Using a broken-down, decomposed, or overly fine potting medium compacts around our roots, blocking air circulation and staying wet for prolonged periods. Furthermore, low temperatures slow down our metabolism and water evaporation, meaning the medium stays wet for longer, increasing the risk of rot.
To prevent our roots from rotting, you must replicate the conditions of our natural home. This means providing a loose, chunky, and extremely well-aerated potting medium, such as large-grade fir bark, sphagnum moss mixed with perlite, or volcanic rock. This type of medium allows water to flow through freely while creating ample air pockets. You must also water us correctly: water us thoroughly until water runs from the drainage holes, and then allow the medium to become almost completely dry before watering again. You can check this by feeling the weight of the pot or looking at the color of our roots; silvery-white means we are thirsty, green means we are hydrated.
Prevention is an ongoing process. Ensure we are potted in a container that is only slightly larger than our root mass and that it has excellent drainage. Repot us every one to two years, or when the potting medium begins to break down and lose its aerating properties. This is also your opportunity to inspect our root system, removing any soft, brown, or mushy roots with sterile tools. Provide us with bright, indirect light and good air movement around our pot; a gentle breeze helps evaporate excess moisture from the potting medium and our leaves, further reducing the risk of rot.
