Osteospermum, commonly known as African Daisy or Cape Daisy, is a genus of flowering plants within the Asteraceae family. Botanically speaking, most Osteospermum species and cultivars are classified as tender perennials. This means they possess the genetic capacity to live for more than two years, regrowing from their root system each spring. However, their specific life cycle—whether they behave as perennials or annuals—is almost entirely dictated by environmental conditions, most critically winter temperatures, rather than an inherent short-lived nature.
The perennial nature of Osteospermum is directly tied to the USDA Plant Hardiness Zone system. These zones, defined by average annual minimum winter temperatures, determine where a plant can survive the cold season and return the following year.
Osteospermum is reliably perennial in USDA zones 9 through 11. In these regions, winter temperatures rarely, if ever, dip below the critical freezing point (20 to 30°F or -6 to -1°C) that would kill the plant's crown and root system. In these warm, mild climates, Osteospermum will establish a woody base and return vigorously for several years, often spreading and forming a dense ground cover.
For gardeners in zones 8 and below, Osteospermum is predominantly grown as a flowering annual. The plant is not frost-tolerant, and exposure to sustained freezing temperatures will be fatal. In these cooler zones, it is planted in the spring after the last frost date, provides prolific blooms from spring through fall, and then completes its life cycle with the first hard freeze of winter. Its inability to survive cold dormancy is what necessitates its treatment as an annual in the majority of North American and European gardens.
Even in colder zones, it is possible to coax a perennial life cycle from Osteospermum through protective measures. In zones 7 and 8, a thick layer of mulch applied over the crown of the plant in late fall can sometimes provide enough insulation for the roots to survive a mild winter. A more reliable method is to grow Osteospermum in containers. Before the first frost, the entire container can be moved to a protected, cool, but frost-free environment such as a garage, greenhouse, or bright sunroom. During this dormancy period, watering should be reduced significantly, allowing the plant to rest without completely drying out. It can then be moved back outside after the danger of frost has passed in the spring.
From a physiological standpoint, newer hybrid cultivars have been developed for specific garden uses, which can influence their longevity. Many modern varieties are bred for compact growth, unique flower colors, and prolific blooming in a single season, prioritizing their performance as annuals. Furthermore, some cultivars may be slightly more cold-tolerant than others, but they rarely gain more than half a zone of hardiness. The species' native South African origin, characterized by mild winters and well-drained soils, is the primary reason for its fundamental sensitivity to cold, wet conditions, which can cause root rot even in borderline perennial zones.
