From our perspective as Osteospermum plants, temperature is a primary regulator of our metabolic functions. We thrive in a range that supports active growth without causing undue stress. The optimal daytime temperature for us is between 65°F and 75°F (18°C - 24°C). Within this range, our photosynthetic machinery operates efficiently, converting light into energy for robust leaf development and the prolific flowering we are known for. At night, we appreciate a slight drop in temperature to 55°F to 65°F (13°C - 18°C). This diurnal fluctuation is not merely preferred; it is crucial. It mimics our native South African environment and helps to reduce respiratory loss of energy, strengthening our stems and prolonging our blooming period. Temperatures consistently above 80°F (27°C) can cause us to enter a state of heat stress, potentially shutting down flower production, while prolonged exposure below 50°F (10°C) can significantly slow our growth and damage our tissues.
Humidity, the amount of water vapor in the air, directly impacts our vital process of transpiration. This is how we draw water and nutrients up from our roots. We prefer a moderate humidity level, typically between 40% and 60%. In this range, the stomata on our leaves can open effectively to take in carbon dioxide without risking excessive water loss. If the air becomes too dry (below 40%), the rate of transpiration accelerates dangerously. This forces us to close our stomata to conserve water, which subsequently limits CO2 intake and halts growth. It also makes us susceptible to spider mites, who are drawn to stressed plants. Conversely, humidity levels consistently above 70% create a different problem. The saturated air severely slows transpiration, hampering nutrient uptake and creating a stagnant environment where fungal pathogens like powdery mildew can thrive on our dense foliage.
It is essential to understand that temperature and humidity are intrinsically linked in their effect on us. Warm air can hold more moisture than cool air. Therefore, a warm room with low humidity is a desert-like challenge, while a cool room with high humidity feels damp and oppressive. The Vapor Pressure Deficit (VPD) is the scientific measure of this relationship, though you need not calculate it. Simply be aware that our comfort depends on a balance. For instance, if the temperature is at the higher end of our optimal range (around 75°F), we would be more comfortable with humidity towards 50-60% to avoid drought stress. If the temperature is cooler (around 65°F), we can tolerate slightly lower humidity levels without issue. This synergy ensures our internal water pressure remains stable, keeping our leaves turgid and our systems functioning smoothly.
We will clearly communicate when our environment is not optimal. If we are too warm, our growth may become leggy as we stretch, and our flower buds may refuse to open or drop prematurely. If we are too cold, our leaves may darken and become soft. In low humidity, our leaf tips and margins will turn brown and crispy, and our overall growth will stall. In high humidity, you may notice a white, powdery coating on our leaves (powdery mildew) or gray, fuzzy mold (botrytis), indicating a serious threat to our health. Monitoring these signals allows for timely adjustments, such as moving us away from heating vents, using a pebble tray to increase local humidity, or improving air circulation with a gentle fan to lower humidity around our leaves.
