From the perspective of a Dendrobium orchid, the primary function of its leaves is photosynthesis and respiration. The leaf surface is covered with a waxy cuticle designed to minimize water loss (transpiration) and protect against pathogen entry. Misting the leaves directly and frequently can disrupt this natural system. A constant film of water on the leaf surface can clog the stomata—the microscopic pores used for gas exchange. If these are blocked, the plant's ability to "breathe" in carbon dioxide and release oxygen is hampered, directly inhibiting its core metabolic process of photosynthesis. Furthermore, water pooling in the crown (where the leaves meet the stem) or in the leaf axils creates a microenvironment that the plant is not adapted for, leading to potential rot.
Dendrobiums, like many epiphytic orchids, naturally thrive in environments with high atmospheric humidity, not wet foliage. They absorb a significant portion of their required moisture from the humid air through their roots and, to a lesser extent, through their leaves. Therefore, the question for the plant is not about having wet leaves but about existing in suitably humid air. Light, occasional misting around the plant (aiming at the air and the potting medium, not the leaves) can temporarily elevate the local humidity, which the plant can utilize through its aerial roots. This mimics the morning dew or humidity of its native habitat. However, this effect is very short-lived without other measures. The plant would vastly prefer a consistently humid environment provided by a humidity tray or a humidifier over sporadic leaf wetness.
A Dendrobium orchid's leaves are highly susceptible to pathogens when conditions are persistently damp. From the plant's viewpoint, standing water on its leaves is an open invitation for fungal spores like Botrytis or bacterial infections like soft rot to establish themselves. These organisms thrive in the stagnant, moist environment that misting can create, especially if water is allowed to sit in the plant's crown overnight. An infection quickly compromises the leaf's tissue, turning it soft, brown, or black, and can swiftly spread to the pseudobulbs and root system, ultimately threatening the plant's survival. The plant's natural defenses are not equipped to handle constant moisture on its surfaces.
Under very specific and controlled circumstances, a Dendrobium might not actively suffer from misting. This is highly dependent on the plant's immediate environment. If the orchid is grown in an exceptionally hot, dry, and well-ventilated space where water evaporates from the leaves within minutes, the risk of rot and disease is significantly reduced. In this scenario, the brief period of leaf wetness might provide a slight cooling effect and a momentary spike in humidity. However, this is a tolerance, not a preference. The plant would still derive more reliable and safer benefit from having its roots watered appropriately and its overall ambient humidity increased through more stable methods.
