African Daisies (Osteospermum spp.) are celebrated for their vibrant, sun-seeking blooms. However, their performance is intrinsically linked to a specific thermal environment. From a plant's physiological perspective, temperature governs every process, from photosynthesis to flowering. To truly flourish, African Daisies require a temperature range that supports robust metabolic activity without inducing stress-related shutdowns.
For sustained growth, photosynthesis, and cellular processes, the ideal air temperature range is between 60°F and 75°F (15°C and 24°C). Within this band, the enzymes responsible for photosynthesis operate at peak efficiency. The stomata on our leaves remain open to readily take in carbon dioxide without risking excessive water loss through transpiration. This allows for the maximum production of sugars, which fuel the development of new stems, leaves, and most importantly, flower buds. Root systems in the soil also actively explore and absorb water and nutrients most effectively when soil temperatures are within this range.
A crucial, and often overlooked, aspect of our ideal temperature cycle is a distinct drop at night. We thrive when nighttime temperatures are consistently 10-15 degrees Fahrenheit cooler than the daytime highs, ideally settling between 50°F and 60°F (10°C and 15°C). This period of cooler rest is not dormancy; it is a vital physiological reset. It reduces our respiratory rate, meaning we burn through the sugars produced during the day at a much slower rate. This conservation of energy allows for greater resource allocation towards bud formation and vibrant flower coloration. Without this cool-down period, our growth can become leggy and flower production may significantly decline.
When temperatures stray outside our comfort zone, our internal systems begin to show clear signs of distress.
• Heat Stress (Above 80°F / 27°C): As temperatures climb, our rate of transpiration skyrockets in an attempt to cool our tissues, risking severe dehydration. To conserve water, we are forced to close our stomata. This action halts the intake of CO2, causing photosynthesis to plummet. The plant's energy is diverted from flowering to pure survival. You will observe this as a cessation of blooming, and the foliage may become limp, wilted, or develop scorched, dry edges. In extreme cases, the plant will enter a state of summer dormancy.
• Cold Stress and Frost Damage (Below 40°F / 4°C): We are not frost-hardy. When temperatures approach freezing, the water within our cells can turn to ice crystals. These crystals physically pierce and destroy the cell membranes, leading to blackened, mushy stems and leaves—a fatal injury. Even non-freezing cold slows our metabolic processes to a near halt, stunting growth and causing leaves to become discolored or purplish due to phosphorus uptake issues.
The initiation of flowering is directly thermoregulated. The ideal daytime range of 60-75°F, coupled with cool nights, provides the perfect signal that conditions are optimal for reproduction. The energy is available, and the stress is low. Prolonged heat, particularly at night, signals that conditions are too arid and stressful for the energetically costly process of producing and maintaining large, showy flowers. Consequently, we will often withhold blooms during the peak of summer heat, waiting for the more favorable temperatures of late spring and early autumn to put on our most spectacular display.
