The name “citronella” refers to two distinct plants, causing confusion about their size and growth habits. The true source of commercial citronella oil is Citronella Grass (Cymbopogon nardus or C. winterianus), a tropical clumping grass. The much smaller plant sold as a garden repellent is the Citronella Geranium (Pelargonium citrosum), a scented geranium with broad, lacy leaves. Understanding the difference between this tall grass and the compact shrub is key to knowing their potential growth.
The Core Answer: Typical Growth Dimensions
Citronella Grass (Cymbopogon nardus) is a tall, tropical plant that develops into a substantial clump when grown as a perennial. In ideal, warm climates (USDA Zones 10–12), it typically reaches 5 to 6 feet tall, and some varieties can grow up to 8 feet. This grass forms a narrow, dense clump that spreads between 3 and 5 feet wide over several growing seasons.
In contrast, the Citronella Geranium (Pelargonium citrosum) is a much more modest plant with a bushy, shrub-like growth pattern. This scented geranium usually achieves a mature height of only 2 to 3 feet tall, with a similar spread. Its growth is compact and manageable, making it a popular choice for containers and patio settings.
Environmental Factors Influencing Size
The ultimate size of both citronella plants depends heavily on the environment, particularly climate and available resources. Plants grown as true perennials in tropical regions (USDA Zones 9–12) reach their maximum growth potential. These warm conditions provide an extended, continuous growing season, allowing them to achieve maximum height.
In cooler climates, both plants are grown as annuals, and their growth is restricted by the short summer season. The growing season often ends before they reach full mature height; Citronella Grass, for example, might only reach 3 to 4 feet tall before the first frost. Consistent sunlight is also important, as both require at least six hours of direct sun daily. Insufficient light causes stems to stretch and become thin, resulting in a leggy appearance instead of a robust size. Rich, well-draining soil and consistent moisture promote vigorous growth, while poor soil or drought stunts the plant’s overall height.
Managing and Controlling Plant Height
Gardeners can actively manage the height of both plants using specific maintenance techniques. For the Citronella Geranium, regular pruning, which involves pinching off the growing tips, encourages a bushier, more compact shape. Plants grown as perennials or overwintered can be cut back by up to one-third in late autumn or early spring to maintain a desirable size.
The size of the container provides a passive means of height control, especially for the large Citronella Grass. Restricting the root system by planting in a smaller pot naturally restricts the plant’s overall growth and final height. Overgrown grass clumps can also be physically divided to control spread and height as the plant matures. Bringing either plant indoors for the winter limits growth cycles, ensuring they restart the following season at a manageable size.