The plant genus Plumbago, often represented by Plumbago auriculata (Cape Plumbago), is a South African native known for its clusters of sky-blue, phlox-like flowers. It blooms prolifically throughout the warmer months and has a naturally sprawling or vining habit, allowing it to be trained up a trellis or used as a mounding shrub. Whether this species acts as a perennial (returning yearly) or an annual (replanted every season) depends entirely on the location and climate.
Defining Annuals and Perennials
The difference between an annual and a perennial plant lies in the length of its life cycle. An annual plant completes its entire life cycle—from germination to seed production and death—within a single growing season, meaning it must be planted fresh each spring.
A perennial plant, by contrast, lives for more than two years. These plants typically survive winter by having their above-ground growth die back while their root systems remain alive in a state of dormancy, ready to regrow when conditions improve.
Plumbago’s Classification by Hardiness Zone
Plumbago auriculata is botanically a weak-stemmed perennial evergreen shrub, meaning it is equipped to live for multiple years. Its ability to act as a true, year-round perennial depends on the climate’s minimum winter temperatures. Plumbago is reliably perennial in USDA Zones 9 through 11, where winter temperatures remain mild.
In these regions, the plant can be left in the ground year-round, often remaining semi-evergreen, and survives winter by going dormant or slowing its growth. While the foliage can tolerate temperatures down to approximately 25°F, it is highly sensitive to sustained freezing temperatures and hard frost, which will cause it to die back or fail to regrow.
In Zones 8 and lower, the plant cannot survive the winter outdoors because freezing temperatures will kill the root system. Gardeners in these colder regions must treat Plumbago as a “tender perennial,” growing it as an annual. It is planted in spring for a single season of bloom and then either discarded or brought indoors before the first frost.
Bringing Plumbago Indoors for Winter
For gardeners outside the perennial hardiness range, overwintering containerized Plumbago indoors is necessary to ensure its multi-year survival. The plant must be brought inside before the first frost, typically when outdoor temperatures drop below 50°F. Before moving it, prune the arching stems back significantly to manage size and encourage new spring growth.
Once inside, the plant can be treated in two ways: kept as an active houseplant or forced into dormancy. To keep it active, place it in a location with bright, natural sunlight, or supplement with a grow light. Forcing dormancy requires moving the pruned plant to a cool, dark location, such as an unheated basement or garage, where temperatures stay above freezing.
During the indoor period, whether active or dormant, the plant requires a substantial reduction in water and fertilizer. Watering should be minimal and infrequent, only enough to prevent the soil from drying out completely. Withholding fertilizer helps maintain a semi-dormant state and prevents weak, leggy growth during low-light winter months.
General Care for Established Plumbago
During its active growing season, Plumbago auriculata performs best when situated in full sun, receiving at least six hours of direct exposure daily. While it tolerates partial shade, insufficient light results in fewer blooms and a less vigorous growth habit.
A well-draining soil mix is necessary for the plant’s health, whether planted in the ground or kept in a container. Although it prefers organically rich soil, it tolerates various soil types, provided water does not accumulate around the roots, as this can lead to root rot. Established plants demonstrate good drought tolerance but benefit from consistent moisture throughout the summer for the best flowering display.
Pruning is an important practice for maintaining the plant’s shape and encouraging continuous blooming. Deadheading spent flower clusters helps extend the bloom period throughout the season. A hard pruning in late winter or early spring is recommended to remove old growth and stimulate the new stems where the most abundant flowers will form.