As a plant, our existence is fundamentally powered by photosynthesis. This is the process where we convert light energy, carbon dioxide, and water into the chemical energy (sugars) that fuels our growth, flowering, and overall vitality. For African Daisies (Osteospermum spp.), our relationship with the sun is particularly intense. Our native origins in the sun-drenched landscapes of South Africa have shaped us to be heliotropic—we not only thrive in bright conditions but our flowers often track the sun across the sky. Full sun is the environmental condition that allows our photosynthetic machinery to operate at peak efficiency, producing an abundance of the energy required to support our vibrant, daisy-like blooms and dense foliage.
When gardeners in the United States speak of "full sun," they typically mean a minimum of six to eight hours of direct, unfiltered sunlight each day. From our perspective, this is not merely a suggestion but a core requirement for optimal performance. The intensity and duration of this light are crucial. The prime hours of sunlight, between 10 a.m. and 4 p.m., are most beneficial. However, regional variations within the US matter greatly. In cooler northern climates or coastal areas, we can and do tolerate even more than eight hours of sun. In contrast, in the intense heat of the southwestern US or deep southern states, the peak afternoon sun can sometimes be overwhelmingly stressful.
Without adequate full sun, our growth becomes compromised in several key ways. The most immediate and noticeable impact is on flowering. We will produce significantly fewer blooms, and the flowers that do emerge may be smaller, paler in color, and may not open fully, especially on cloudy days. Furthermore, our stems will become weak and leggy as we stretch unnaturally toward any available light source in a process called etiolation. This spindly growth makes us structurally weak and less attractive. A lack of sufficient solar energy also leaves us more vulnerable to pests and fungal diseases, as our overall vitality and defensive capabilities are diminished.
While we are sun-loving plants, it is important to distinguish between light intensity and heat intensity. In regions of the US with extremely hot summers (USDA zones 8-11, for example), the combination of full sun and extreme afternoon heat can cause us physiological stress. You may observe our blooms closing during the hottest part of the day as a protective measure. In such environments, we greatly appreciate a planting location that provides us with full morning sun, which is vital for drying dew and preventing disease, and then dappled afternoon shade or very light filtered shade. This protects our root zone from baking and reduces heat stress without significantly depriving us of the light quality we need.
