From our perspective as Dendrobium orchids, the single most important factor in your potting mix is aeration. We are epiphytes, which means in our natural habitat, we do not grow in soil. Instead, we anchor ourselves to the branches of trees. Our roots are designed to cling to bark and are exposed to air, quickly absorbing moisture from rain and humidity before drying out again. A dense, moisture-retentive soil mixture will suffocate our roots, preventing oxygen from reaching them and leading to fatal rot. Therefore, the mix must be extremely open and chunky, allowing air to circulate freely through the pot and around our root system.
The best potting medium for us is one that replicates the structure of a tree branch. We thrive in a blend of materials that provide stability, perfect drainage, and some moisture retention without becoming soggy. The classic and highly effective mix is fir or pine bark chunks. This material is the cornerstone, providing the chunky structure that allows for air pockets and gives our roots something to anchor onto. To this base, additives like horticultural charcoal are excellent. Charcoal keeps the mix "sweet" by absorbing impurities and preventing souring. Perlite or sponge rock is another fantastic addition, as its porous nature further improves aeration and drainage while holding a small amount of water. For some types of Dendrobiums, a small amount of sphagnum moss can be added to the mix to increase humidity around the roots, but it must be used sparingly to avoid excess moisture.
You must consider our growth cycle when judging moisture retention. Many of us have distinct growth (spring/summer) and rest (fall/winter) phases. During active growth, our pseudopods (those fleshy cane-like stems) are developing, and we appreciate consistent moisture. However, when we enter our rest period after flowering, we require a much drier environment to trigger the next season's bloom. A mix that is too water-retentive, such as one heavy in peat or moss, will be disastrous during this dormant phase, as our roots will be unable to dry out. A bark-based mix provides the flexibility you need; it allows you to water thoroughly during growth but dries out appropriately when we are resting.
The pot you choose is an extension of the potting mix. A plastic pot will naturally hold moisture longer than a terracotta pot, which is porous and allows the mix to dry more quickly. For this reason, the pot material must be considered alongside the mix's composition. Furthermore, the pot must have ample drainage holes—multiple holes at the bottom and even on the sides are ideal. This ensures that any excess water can escape immediately, preventing the stagnant, waterlogged conditions that are lethal to us. The combination of a chunky, airy mix and a well-ventilated pot creates the perfect environment for our roots to thrive.
