Osteospermum, commonly known as African Daisy or Cape Daisy, is botanically classified as a tender perennial. This means the plant possesses the genetic and physiological capacity to live for more than two years, completing its life cycle over multiple growing seasons. Its native habitat is the temperate regions of South Africa, which experience mild, frost-free winters. This origin is the primary determinant of its cold sensitivity. The plant's vascular system and cellular structure are not adapted to withstand freezing temperatures; ice crystals form within the plant tissues, causing irreversible damage to cell walls and leading to plant death. Therefore, its perennial nature is entirely conditional on environmental factors, primarily winter temperature minima.
Your specific US region, defined by its USDA Plant Hardiness Zone, is the critical factor that determines whether Osteospermum will behave as a perennial or an annual. The USDA zone map is based on the average annual extreme minimum winter temperature. Osteospermum is reliably winter hardy only in zones 10 and 11, where temperatures rarely, if ever, dip below 30°F (-1°C) to 35°F (2°C). In these frost-free climates, the plants will survive the winter, often going semi-dormant, and resume vigorous growth and flowering the following spring, unequivocally acting as perennials.
For the vast majority of the United States, which falls within USDA zones 1 through 9, Osteospermum is functionally an annual. When planted in the spring after the last frost date, it will grow, flower profusely throughout the summer and into the fall, and then be killed by the first hard freeze of winter. Its life cycle is condensed into a single growing season. The plant's prolific flowering is a reproductive strategy to set seed before the onset of lethal conditions, ensuring the propagation of its genetic line even if the individual parent plant dies.
Even in colder zones, it is possible to coax a perennial life cycle from Osteospermum through human intervention, mimicking its preferred conditions. The most effective method is to grow the plant in containers. Before the first frost, the entire container can be moved indoors to a protected location. Ideal overwintering sites are cool, bright spaces such as an unheated garage, a sunny basement, or a greenhouse where temperatures consistently remain between 40-50°F (4-10°C). During this dormancy period, water should be drastically reduced, providing just enough to prevent the soil from becoming bone dry and the roots from desiccating completely. The plant will likely not flower but will conserve energy to regrow when placed back outside after the danger of frost has passed in the spring.
