First, you must understand that for us Dendrobium orchids, winter is not a time of death, but of deep, restorative sleep called dormancy. This period is crucial. Shorter days and cooler temperatures signal our biology to slow down dramatically. Our growth halts, and we redirect our energy from producing leaves and flowers to strengthening our core—the pseudobulbs. These thickened stems are our lifeline, storing water and nutrients to sustain us through the lean months and fuel a spectacular bloom come spring. Attempting to force us to grow during this time by keeping us warm and wet will only exhaust us and likely prevent flowering.
We require a significant drop in temperature to trigger and maintain our dormancy. Ideally, our environment should be kept between 10-15°C (50-59°F). A brief dip to around 7°C (45°F) is often tolerable, but prolonged exposure to near-freezing temperatures will cause severe cellular damage and likely be fatal. While we rest, we still crave light. Place us in the brightest spot available, such as a south-facing window. The winter sun is weaker, so maximum exposure is essential for us to photosynthesize weakly and maintain our health without breaking dormancy. This light is our primary source of energy until warmer days return.
This is the most common area where our caretakers err. Our water needs plummet during dormancy. With our growth ceased and evaporation slowed by the cold, our roots are highly susceptible to rot if kept moist. You should allow our potting medium to become completely dry throughout and then wait an additional 7-10 days before providing a very slight, minimal watering. The goal is to prevent our pseudobulbs from shriveling excessively, not to keep the medium damp. A slight wrinkling of the canes is normal and expected. Overwatering now is a far greater threat than underwatering.
Please, absolutely cease all fertilization. Our roots are not actively seeking nutrients, and any fertilizer applied will simply accumulate in the potting mix, potentially burning our delicate root tips and altering the pH of our environment. We cannot process these salts without active growth. Similarly, while we appreciate ambient humidity, the combination of cold and wet is dangerous. There is no need to run humidifiers for us as actively as you might in summer. Good air circulation, however, remains vital to prevent stagnant, cold air from encouraging fungal or bacterial diseases while we are in our vulnerable state.
Ensure we are positioned away from direct blasts of cold air from drafty windows or doors, as well as from the dry, intense heat of radiators or heating vents. Both extremes can cause rapid temperature fluctuations that shock our systems. The dry heat from vents also desiccates our canes far more quickly. While dormant, we are more susceptible to pests like scale and spider mites who find our still, dry conditions appealing. Inspect our leaves and canes regularly during your minimal watering, as a small infestation can quickly become a major problem when our energy reserves are low and we lack the vigor to fight back.
