Osteospermum, commonly known as the African Daisy or Cape Daisy, is a flowering plant prized for its vibrant, daisy-like blooms. Native to South Africa, it is inherently adapted to a specific climatic range. From the plant's perspective, its ability to tolerate heat is a complex interplay of its genetic programming, physiological processes, and environmental conditions.
For an Osteospermum plant, the ideal temperature range for active growth, photosynthesis, and prolific flowering is between 60°F and 75°F (15°C to 24°C). Within this range, the plant's enzymatic activity, water uptake, and nutrient absorption operate at peak efficiency. The stomata on the undersides of the leaves remain open to facilitate gas exchange (taking in CO2 and releasing oxygen and water vapor) without risking excessive dehydration. This results in healthy foliage and a continuous display of flowers.
Osteospermum can handle and even thrive in temperatures up to approximately 85°F to 90°F (29°C to 32°C), especially if it is acclimated and other conditions are favorable. However, this is the upper threshold where heat stress begins. Beyond this point, the plant's survival mechanisms are triggered. To conserve precious water, the stomata will begin to close. While this reduces water loss, it also severely limits the intake of CO2, bringing photosynthesis—the process of creating energy—to a near halt. The plant essentially enters a state of conservation, prioritizing survival over growth and reproduction.
When faced with prolonged heat above 90°F (32°C), the plant exhibits clear signs of distress. The most visible response is wilting; leaves and stems become limp as water loss through transpiration exceeds the root system's ability to draw it from the soil. If the stress continues, flower production will cease entirely, and existing blooms may wither rapidly. The plant redirects all energy away from flowering to maintain basic cellular functions. Intense, direct afternoon sun combined with high heat can also lead to sunscald, causing bleached, papery, or scorched patches on the leaves and petals, effectively damaging the plant's food-making factories.
The plant's experience of heat is not solely determined by air temperature. Several factors can raise or lower its effective tolerance. Ample soil moisture is critical; a well-hydrated root system can support higher rates of cooling transpiration. Conversely, heat combined with drought is exponentially more damaging. Airflow is another crucial factor; a slight breeze helps carry away heat and reduces the boundary layer around the leaf, easing transpiration. Furthermore, a plant that has been gradually exposed to increasing warmth (hardened off) will tolerate heat far better than one suddenly subjected to a heatwave, as it has had time to produce protective antioxidants and heat-shock proteins.
