The Four O’Clock (Mirabilis jalapa) often confuses gardeners regarding its longevity. Originating in tropical regions, this species is fundamentally a tender perennial, meaning it can live for more than two years. However, its survival as a perennial depends entirely on the climate, specifically the presence or absence of deep, sustained ground frost. For most cultivators, it is treated as a seasonal plant that requires management to return the following year.
Defining the Four O’Clock Life Cycle
The designation of Mirabilis jalapa as a tender perennial stems from its root structure, which forms a large, fleshy, tuberous root system. This tuber acts as an underground storage organ, accumulating energy to allow the plant to survive dormancy and regrow when conditions are favorable. In warm environments, the plant naturally dies back in winter and reliably sprouts from this tuber in the spring, making it a true perennial.
Year-round survival in the ground is restricted to regions with minimal freezing temperatures, generally USDA Hardiness Zones 9 through 11. In these zones, the soil does not freeze deeply enough to damage the underground tuber, allowing the plant to persist indefinitely. The plant enters a period of rest, shedding its above-ground foliage before resuming growth.
For gardeners in colder climates (Zone 8 and below), the tuber cannot withstand prolonged, sub-freezing temperatures. When the ground freezes solid, the water within the root cells expands, rupturing the tissues and causing the tuber to rot. This biological limitation forces cultivation practices to shift, and the Four O’Clock is functionally grown as a warm-weather annual, completing its life cycle within a single season unless human intervention occurs.
Overwintering and Tuber Storage
To ensure the return of a mature Four O’Clock in cold regions, the tuberous root must be removed from the ground and stored indoors. This process, called “lifting,” begins after the foliage is killed by the first light frost in autumn. The frost signals the plant to cease growth and transfer energy reserves to the underground tuber.
After the top growth has withered, trim the stems back to a few inches above the soil line. Carefully dig up the tuber, avoiding damage to the large, carrot-like root. Brush away excess soil, and then leave the tuber in a cool, dry place for a few days to “cure.” Curing allows the outer skin to dry and harden.
Proper storage involves placing the cured tubers in a container filled with a dry, slightly moisture-retaining medium, such as peat moss, dry sand, or wood shavings. This prevents the tuber from drying out while protecting it from rot. Stored tubers require a cool, dark, and frost-free location, with an ideal temperature range between 40 and 50 degrees Fahrenheit, such as a basement or unheated garage. Replant the tubers directly into the garden in the spring once the danger of the last frost has passed and the soil has warmed.
Basic Growth Habits and Care
The common name “Four O’Clock” is derived from the plant’s distinct habit of opening its colorful, trumpet-shaped flowers in the late afternoon. These fragrant blooms remain open overnight, closing by the following morning as sunlight intensity increases. This pattern makes them especially attractive to nocturnal pollinators like sphinx moths. The plant thrives in full sun but tolerates partial shade, especially where summer afternoons are intensely hot.
Four O’Clocks prefer moderately fertile, well-drained soil that is kept consistently moist throughout the growing season. The plant typically reaches a bushy height of two to three feet, providing a dense, shrub-like appearance. A significant trait is its robust self-seeding capability, producing numerous black, hard-shelled seeds that readily germinate the following spring. This natural proliferation often leads gardeners to believe the original plant survived when, in reality, a new generation has taken its place.