Osteospermum, commonly known as African daisy, originates from South Africa, where it thrives in warm, sunny climates with well-drained soil. This perennial plant is adapted to mild winters and hot summers, making it sensitive to freezing temperatures. Its natural habitat provides clues about its cold tolerance: it is not inherently equipped to survive harsh winter conditions outdoors in colder regions.
Osteospermum is typically classified as hardy in USDA zones 9-11, where winter temperatures rarely drop below 20°F (-6°C). In these zones, it may survive outdoors with minimal protection. However, in zones 8 or lower, where temperatures frequently fall below freezing, Osteospermum is unlikely to survive winter without significant intervention. Prolonged exposure to frost or snow can damage or kill the plant, as its tissues are not frost-resistant.
When exposed to cold, Osteospermum exhibits several physiological stress responses. Its cell membranes may rupture due to ice crystal formation, leading to dehydration and cell death. The plant's metabolic processes slow down, reducing growth and nutrient uptake. Unlike hardy perennials, Osteospermum lacks adaptations like deep root systems or antifreeze proteins, making it vulnerable to winter conditions.
In marginally cold regions (e.g., zone 8), Osteospermum may survive winter if provided with protection. Mulching around the base insulates roots, while covering the plant with frost cloth can shield it from freezing winds. Planting in sheltered locations, such as near south-facing walls, can also mitigate cold damage. However, these measures are not foolproof and depend on the severity of winter.
In zones below 8, Osteospermum is often treated as an annual or overwintered indoors. To preserve the plant, dig it up before the first frost and pot it in well-draining soil. Place it in a bright, cool (50-60°F/10-15°C) indoor location, reducing watering to mimic dormancy. Alternatively, take cuttings in late summer to propagate new plants indoors for spring replanting.
Gardeners in colder zones may opt for cold-tolerant Osteospermum cultivars, though these are rare. Another approach is to grow the plant in containers, allowing it to be moved indoors during winter. While this requires more effort, it ensures the plant's survival and reduces the need for replanting each year.
If Osteospermum is exposed to cold, signs of damage include wilted, blackened foliage and stunted growth. Prune dead material in early spring to encourage regrowth, but recovery is unlikely if roots are frozen. In mild cases, new shoots may emerge from the base if the root zone survives.
