From a plant's perspective, the ideal temperature range for impatiens is a narrow band that feels neither too hot nor too cold, allowing for optimal physiological function. This sweet spot is between 65°F and 75°F (18°C and 24°C). Within this range, our cellular processes, particularly photosynthesis and respiration, operate at peak efficiency. Enzymes responsible for converting sunlight into energy work flawlessly, roots actively absorb water and nutrients, and we can direct our energy into our primary purpose: producing a spectacular, continuous display of vibrant blooms. The stems grow strong and sturdy, the foliage remains a deep, healthy green, and the risk of stress-induced diseases is minimized. This is the condition we strive for.
When temperatures consistently rise above 80°F (27°C), we enter a state of significant stress. Our rate of transpiration (water loss through our leaves) skyrockets, often exceeding the root system's ability to draw up moisture from the soil. This leads to wilting, a desperate attempt to conserve water by reducing leaf surface area. Prolonged heat forces us to divert energy away from flowering and into mere survival. Bloom production slows dramatically or halts entirely, and existing flowers may drop or wither prematurely. Furthermore, high heat weakens our defenses, making us far more susceptible to pests like spider mites, which thrive in hot, dry conditions, and fungal diseases such as powdery mildew.
Conversely, temperatures dipping below 50°F (10°C) are equally problematic and potentially fatal. We are tropical understory plants, and cold is our enemy. Chilly conditions cause our growth to slow to a crawl or stop completely. Our leaves may take on a reddish or purplish tint, a sign of phosphorous uptake issues and cold stress. The most critical threshold is 32°F (0°C). Exposure to frost causes the water within our cells to freeze, forming ice crystals that rupture and destroy the cell walls. This damage is irreversible and manifests as blackened, mushy foliage and stems. A single frost event is almost always lethal, as our succulent tissues cannot withstand freezing temperatures.
While daytime warmth is crucial for photosynthesis, the temperature during the night is equally critical for our well-being. We perform respiration at night, breaking down sugars for energy and growth. An ideal night temperature range is between 55°F and 65°F (13°C and 18°C). If nights remain too warm (above 70°F or 21°C), our respiration rate increases, causing us to burn through the energy we stored during the day at an unsustainable rate. This leads to spindly, weak growth as we desperately stretch for resources. A noticeable drop in temperature at night is not just preferred; it is physiologically necessary for maintaining robust health and conserving energy for flowering.
