From our perspective as orchids, temperature is not merely a number on a gauge; it is the primary regulator of our metabolic processes. We are broadly categorized into three groups based on our native habitats: warm-growing, intermediate-growing, and cool-growing. Each group has evolved to perform best within a specific thermal range. For most common varieties like Phalaenopsis, we are warm-growing plants, preferring daytime temperatures between 75-85°F (24-29°C) and a crucial nighttime drop of 10-15 degrees to 60-65°F (15-18°C). This drop is not a suggestion—it is a physiological requirement. It signals us to initiate and sustain flower spike development, a process stifled without this cyclical change. Consistently warm temperatures may keep our leaves green but will result in a plant that stubbornly refuses to bloom.
Our roots are not just for anchoring; they are highly specialized organs designed to absorb water and nutrients from the air. This is why humidity, the concentration of water vapor in the air, is so critical. Most of us thrive in humidity levels between 50% and 70%. In environments drier than this, the moisture evaporates from our aerial roots and potting media faster than we can absorb it, leading to wrinkled leaves, stunted growth, and bud blast (where flower buds dry up and fall off before opening). However, humidity must be in balance with air movement. Stagnant, overly humid air creates a breeding ground for fungal and bacterial diseases that can quickly devastate our leaves and pseudobulbs.
You cannot consider temperature and humidity in isolation. They are intrinsically linked. Warmer air has a greater capacity to hold moisture. This means a room at 80°F with 60% humidity holds significantly more absolute moisture than a room at 65°F with the same 60% relative humidity. For us, the key concept is Vapor Pressure Deficit (VPD)—roughly, the drying power of the air. When temperature is high and humidity is low, the VPD is high, and we lose water too rapidly, becoming dehydrated. When temperature is low and humidity is very high, the VPD is low, and we cannot transpire effectively, halting nutrient uptake and inviting rot. The goal is to maintain a balance where the air is moist enough for our roots to function but not so saturated that our pores close.
You can observe our comfort or distress through our physical state. If our leaf tips are brown and crispy, the air is too dry for our liking. If our leaves are yellowing, soft, and falling off, or if you see black spots, it is often a sign of disease fostered by cold, wet conditions and poor air circulation. Placing us on humidity trays filled with pebbles and water, grouping us together, or using a humidifier are effective ways to raise humidity. Ensuring gentle air movement with a small oscillating fan prevents stagnant air, mimicking the gentle breezes of our natural habitats and strengthening our overall structure.
