The classification of a citronella plant as an annual or perennial depends entirely on the local climate and the specific plant being discussed. Most garden centers sell a plant labeled “citronella” that is not the true source of the famous essential oil, adding confusion to its proper classification. Both plants are cold-sensitive, meaning they are perennials only in the warmest regions, requiring special care or replanting elsewhere.
Clarifying the Identity: Scented Geranium vs. Lemongrass
The term “citronella plant” is commonly applied to two distinct botanical species, leading to frequent misidentification. The plant most often seen in garden centers is the Scented Geranium, Pelargonium citrosum ‘Citronella’. This subshrub is a member of the Geraniaceae family, featuring deeply cut, lacy green leaves that release a lemon scent when bruised. It grows relatively bushy, typically reaching two to three feet in height and width, and produces small, lavender-pink blooms.
The true source of commercial citronella oil is a tropical grass species, Cymbopogon nardus or Cymbopogon winterianus, known as Citronella Grass. This species belongs to the Poaceae family and is related to culinary lemongrass, growing in tall, dense clumps up to six feet high. Citronella Grass is characterized by long, coarse, upright stems, which contrast sharply with the geranium’s delicate foliage. Only the Cymbopogon species contains the essential oil used in repellent products.
Determining the Life Cycle by Climate
The designation of either plant as an annual or a perennial is tied to its native tropical origins and the minimum winter temperatures of the planting location. A perennial lives for more than two years, while an annual completes its life cycle within a single season. Both the Scented Geranium and the Citronella Grass are classified as tender perennials, meaning they cannot tolerate freezing temperatures.
The Scented Geranium (Pelargonium citrosum) is reliably perennial only in USDA Hardiness Zones 9 through 11. In these warm regions, the plant can develop a woody base and survive outdoors year-round. In Zones 8 and colder, the plant is not frost-hardy and will die back completely. Gardeners in colder climates must treat the Scented Geranium as an annual, replanting it each spring, or bring it indoors for the winter months.
Citronella Grass (Cymbopogon species) requires consistently warm conditions to be classified as a true perennial. This tropical grass thrives in USDA Zones 10 through 12, where it grows into a sizable, long-lived clump. Outside of these zones, the plant is grown as an annual because it is highly sensitive to frost.
Seasonal Care and Overwintering
For gardeners who treat the Scented Geranium as a perennial, successful overwintering relies on moving the plant indoors before the first hard freeze arrives. The plant should be brought inside when nighttime temperatures consistently drop below 45 degrees Fahrenheit, as frost will damage the foliage. Before relocating the container, thoroughly inspect the foliage for common pests like aphids or mealybugs, which can be dislodged with a strong spray of water before the move.
The plant should be pruned back by as much as one-third, with cuts made just above a leaf node to encourage healthy, bushy regrowth. This reduction in size helps the plant transition to lower light conditions and prevents it from becoming overly leggy indoors. Any dead or damaged leaves should also be removed to improve air circulation and discourage fungal issues during its indoor stay.
Once indoors, the Scented Geranium requires a significant reduction in water, as its growth slows considerably during the winter dormancy period. The soil should be allowed to dry out slightly between waterings, preventing the root rot that often occurs from excess moisture in cool indoor conditions. Providing ample light is also important, with a sunny south- or west-facing window being the most suitable location for the container. During the dormant period, the plant may benefit from a light feeding of liquid fertilizer, diluted to half-strength, applied once or twice throughout the winter months.