Osteospermum, commonly known as the African Daisy, is a perennial plant that originates from the warm, temperate regions of South Africa. Its fundamental nature is that of a tender perennial, meaning its ability to survive winter is intrinsically linked to the severity of the cold. Its survival strategy is not one of deep dormancy and extreme cold tolerance like a deciduous tree, but rather one of mild-climate persistence. From our perspective, the concept of winter hardiness is a matter of cellular integrity; when temperatures drop below a certain point, the water within our cells freezes, forming ice crystals that rupture cell walls, leading to irreversible damage and death.
For the Osteospermum plant, the ideal conditions for perennial survival are found within USDA Plant Hardiness Zones 9 through 11. In these zones, winter low temperatures typically remain above 20°F to 30°F (-6.7°C to -1.1°C). Within this range, our systems can remain active, albeit slower, without experiencing fatal freeze damage. We may experience some die-back of the most tender top growth if a brief cold snap occurs, but our root crown and core structure remain protected and viable. In Zone 9, a protective layer of mulch is often welcomed by us to buffer the root zone against occasional dips toward the lower temperature threshold.
In the vast regions classified as Zones 8 and below, winter presents a mortal threat. When temperatures consistently fall below 20°F (-6.7°C), the freezing event penetrates the soil, reaching our root system. This causes the fatal cellular damage described. Therefore, in these climates, we complete our entire life cycle—germination, vegetative growth, flowering, and seed setting—within a single growing season. We are treated as annuals. While we cannot survive the winter in the ground, we often flower profusely until the first hard frost, providing vibrant color until the very end of the season.
Our survival is not solely dictated by the broad USDA zone map. Microclimates can create small pockets of warmer conditions. A south-facing wall that absorbs daytime heat, a sheltered courtyard, or a well-drained slope can sometimes provide just enough protection for us to survive a milder winter in Zone 7b or 8. Furthermore, attentive gardeners can extend our life by employing protective measures such as a thick, dry mulch blanket over our crown or using frost cloth during the coldest nights. In containers, we can be moved to a sheltered, unheated garage or greenhouse where temperatures stay above freezing, allowing us to enter a state of semi-dormancy until spring.
It is important to note that not all Osteospermum are genetically identical. Through selective breeding, some newer cultivars have been developed with slightly improved cold tolerance. Certain varieties may boast resilience into the lower range of Zone 8, perhaps surviving lows of 15°F (-9.4°C) with excellent drainage and protection. When selecting a plant, it is always advisable to check the specific cultivar's stated hardiness, as it may offer a slight advantage over the general species guideline.
