The Cape Plumbago, scientifically known as Plumbago auriculata, is a popular ornamental shrub appreciated for its long-lasting, sky-blue flowers. This fast-growing plant is native to South Africa, thriving in warm, subtropical climates. Gardeners prize it for its continuous color and relative ease of care, making it a common choice for hedges, trellises, and containers.
Defining Mature Dimensions
The mature size of plumbago depends significantly on how it is cultivated. As a free-standing, sprawling shrub, it typically reaches a height of 6 to 10 feet with a similar spread of 6 to 8 feet wide in ideal conditions. This plant has a naturally arching, sprawling habit, and its weak stems tend to spread horizontally, forming a large, rounded mound if left untrimmed. Plumbago auriculata is a rapid grower that can reach its full size within a year or two once established.
The plant’s dimensions can increase dramatically when its climbing potential is utilized. While it is naturally a shrub, its flexible branches allow it to be trained as a vine, requiring support like a trellis or fence. When grown vertically with assistance, plumbago can reach heights of 15 feet or more. Even in containers, where growth is restricted, the plant can still attain a manageable height of 1 to 3 feet, though regular pruning remains necessary to maintain a compact shape.
Environmental Factors Influencing Growth
The wide range in plumbago’s potential size is directly related to the environmental conditions it experiences. As a perennial, the plant achieves its maximum dimensions only in frost-free regions, specifically USDA Hardiness Zones 9 through 11, where it grows year-round without interruption. In these tropical zones, the plant behaves as an evergreen shrub, allowing its woody structure to mature fully.
Climate and Frost
In cooler climates, such as Zone 8 or lower, the plant is often grown as an annual or experiences winter dieback when temperatures drop below freezing. If the top growth is killed by frost, the plant must regrow from the roots each spring, which severely limits its overall size.
Light and Soil
Plumbago performs best and grows largest when planted in full sun, receiving six or more hours of direct light daily, as this promotes vigorous growth and abundant flowering. While it tolerates partial shade, reduced light often results in leggier stems and a less dense growth habit. Rich, well-draining soil and consistent moisture during the growing season support greater height and spread than poor, dry, or compacted soil conditions.
Controlling Size Through Pruning
Because of its fast growth rate and sprawling nature, regular pruning is required for maintaining a desired size and shape. The best time for major size reduction, known as rejuvenation pruning, is in late winter or early spring before new growth begins. During this period, you can safely cut the plant back drastically, removing up to one-third of the total growth to manage excessive height or spread.
This heavy pruning encourages a flush of new growth, which is important because plumbago flowers exclusively on new wood. Throughout the growing season, a lighter maintenance pruning can be performed to keep the plant in bounds and promote continuous blooming. This involves trimming back long, arching branches that extend beyond the intended perimeter. For gardeners aiming to keep the plant significantly smaller, such as 3 or 4 feet tall for a low hedge, consistent annual hard pruning is required. Deadheading spent flower clusters also helps redirect the plant’s energy from seed production, contributing to a denser and more compact form.