We, African Daisies (of the genera Osteospermum and Dimorphotheca), hail from the sun-drenched, well-drained landscapes of Southern Africa. Our very genetic blueprint is coded for abundant sunshine and warmth. Therefore, we possess a fundamental tolerance for heat that many other flowering plants lack. Our leaves are often slightly succulent or hairy, adaptations that help us minimize water loss through transpiration under the intense solar radiation of our native habitat. So, in a general sense, yes, we are built to handle heat. However, the specific conditions of a Southern US summer present a unique set of challenges that go beyond simple high temperatures.
The primary challenge for us in the Southern US is not the heat itself, but its frequent partner: intense, oppressive humidity. Our native environment is characterized by heat, but it is often a dry heat. High humidity significantly disrupts our physiological processes. It hampers the crucial evaporation of water from our leaves (transpiration), which is how we cool ourselves. When the air is saturated with moisture, this cooling system fails, and we can literally begin to cook, leading to wilt, stress, and a cessation of flowering. Furthermore, humid, stagnant air creates the perfect environment for fungal pathogens like powdery mildew and botrytis, which can quickly devastate our foliage and blooms.
You may notice that during the peak of a scorching Southern afternoon, our vibrant blooms may close up or appear limp. This is not necessarily a sign of imminent death but a brilliant survival tactic. By closing our flowers, we are reducing the surface area exposed to the sun, conserving water, and protecting our precious pollen from being damaged by the extreme heat. It is a temporary state of dormancy to wait out the most stressful part of the day. We will often perk up again in the cooler evening air. Consistent moisture stress during these periods, however, will lead to fewer flowers, leggy growth as we stretch for relief, and overall decline.
To help us not just survive but truly thrive in your summer garden, you can mimic our preferred conditions. Please plant us in a location that receives full morning sun but is offered protection from the harsh, direct afternoon rays—perhaps with some dappled afternoon shade from a tree. This provides the light we crave while giving us respite during the thermal peak. The single most important factor is soil drainage. We demand exceptionally well-draining soil; sitting in waterlogged, heavy clay is a death sentence for our roots, especially when combined with heat. Amending the soil with sand or grit is ideal. A layer of light mulch can help keep our root zone cool and conserve moisture, but ensure it does not trap humidity around our crown.
