First, you must understand that for many of us Dendrobium species (like the popular Den. nobile types), winter is not a time for growth, but for essential rest. We are not dead; we are dormant. Shorter days and cooler temperatures signal our biology to slow down dramatically. This period of cool, dry rest is absolutely critical for initiating the development of flower buds on our older canes. Without this seasonal cue, we may continue to produce vegetative growth (keikis) instead of the beautiful blooms you cherish. Think of it as our long, deep sleep to gather energy for a spectacular spring performance.
Our temperature needs shift significantly in winter. While we thrive in warmth during the growing season, we now require a distinct drop in temperature to trigger dormancy and subsequent flowering. For most of us, ideal winter nights should be consistently between 50-60°F (10-15°C), with daytime temperatures only slightly warmer. A protected porch, a cool sunroom, or even a windowsill away from indoor heating vents can provide this perfect microclimate. Crucially, we must be protected from freezing temperatures and frost, which will cause severe cellular damage and are often fatal. A sudden cold draft from an opened window can be just as damaging as sustained cold.
This is perhaps the most difficult change for our caregivers to master. As our growth ceases, our water requirements plummet. You must significantly reduce the frequency of watering. For many deciduous Dendrobiums, a good rule is to provide just enough water to prevent our pseudobulbs (canes) from shriveling excessively. This might mean a thorough watering only every two to three weeks, or even just monthly, depending on your humidity and light levels. Soggy, cold roots are a death sentence for us in winter, leading to rapid root rot. It is far safer for us to be too dry than too wet during this sensitive period.
Even in dormancy, we still crave bright, indirect light. The winter sun is weaker, so a south or east-facing window is ideal to maximize the available light energy. This helps keep our canes strong and healthy while we rest. However, you must completely cease all fertilization. Our roots are not actively seeking nutrients, and any applied fertilizer will simply accumulate in the potting medium, potentially burning our delicate root tips and altering the pH of the bark. We have stored all the energy we need for flowering within our existing canes; your job is simply to protect that stored energy until spring.
Winter air indoors is often very dry due to heating systems, which can cause our canes to desiccate more than is ideal. While we need less water at our roots, we still benefit from moderate ambient humidity. Placing our pot on a humidity tray filled with pebbles and water (ensuring the pot never sits *in* the water) can create a helpful microclimate. Gentle air movement is also vital to prevent stagnant, moist air from settling around us and encouraging fungal or bacterial diseases. A ceiling fan on low or an oscillating fan set at a distance provides perfect, gentle airflow.
