The term “citronella plant” is widely used by gardeners and consumers to describe fragrant foliage believed to deter flying insects. This common name refers to a plant that emits a distinct, bright citrus scent when its leaves are disturbed or bruised. This powerful aroma has led to its reputation as a natural bug deterrent, and its oils are the source for ingredients in commercial repellents like candles and sprays. This popular perception, however, masks significant botanical confusion regarding the plant’s true identity and its actual ability to keep mosquitoes away.
The Identity Crisis: True Citronella Grass vs. Scented Geranium
The name “citronella plant” actually applies to two distinct species, leading to widespread public misunderstanding. The first is the true source of the commercial essential oil, which is a perennial grass of the genus Cymbopogon, specifically Cymbopogon nardus or Cymbopogon winterianus. This tropical grass, related to culinary lemongrass, contains high concentrations of the compounds used in repellents.
The second, and far more common plant sold under names like “citronella plant” or “mosquito plant,” is a scented geranium, Pelargonium citrosum or a similar hybrid. This plant is a bushy, flowering perennial that is typically grown as an annual outside of tropical climates.
The visual differences between the two are notable. The true citronella grass grows in tall, coarse clumps, reaching heights of five to six feet with long, flat, grayish-green blades. The scented geranium, by contrast, is much shorter, usually staying under two feet tall, and features lacy, deeply lobed leaves. While both plants release a lemon-like fragrance when their leaves are crushed, they belong to entirely separate plant families. Understanding this distinction is fundamental because the identity of the plant directly relates to its use and care.
Cultivation and Care Requirements
The two plants commonly referred to as citronella share some overlapping care needs but also exhibit distinct preferences for water and soil. Both the Cymbopogon grass and the Pelargonium geranium thrive when given ample sunlight, generally requiring at least six to eight hours of direct sun daily to maximize their growth and fragrance production. Since both are tropical or subtropical in origin, they are typically grown as seasonal annuals in temperate regions, as they cannot survive freezing temperatures.
The true citronella grass requires a long, warm growing season and needs consistent moisture to support its rapid, tall growth. It prefers rich, well-drained soil and needs regular watering to maintain the humidity levels it favors. Propagating this grass is typically done by dividing its dense clumps, as it does not readily produce viable seeds in most garden settings.
The scented geranium, Pelargonium citrosum, is comparatively drought-tolerant once established. It should be planted in fertile, well-draining soil and only needs to be watered when the top inch or two of soil has become dry to the touch. Due to its more compact and manageable size, this geranium is a popular choice for containers and can easily be overwintered indoors near a sunny window.
The Truth About Mosquito Repellency
The effectiveness of the citronella plant in repelling mosquitoes depends entirely on which plant is being discussed and how its compounds are utilized. The essential oil derived from the true citronella grass (Cymbopogon nardus or C. winterianus) contains high levels of the chemical compounds citronellal and geraniol. When this oil is extracted, concentrated, and applied topically or released into the air by burning, it works by overwhelming the olfactory receptors of mosquitoes, making it harder for them to locate a host.
Scientific studies confirm that citronella oil is an effective repellent when used in a concentrated form, such as in lotions or candles, though its duration of protection is often shorter than synthetic alternatives like DEET.
However, simply growing the intact plant, whether it is the grass or the scented geranium, provides minimal to no protection against mosquitoes. The plants do not release enough of the fragrant oil into the air naturally to create a repellent barrier.
The common scented geranium, Pelargonium citrosum, is particularly ineffective because it contains a negligible concentration of citronellal compared to the commercial oil source. To obtain even a fleeting repellent effect from either plant, the leaves must be crushed or bruised, which manually releases the volatile oils onto the skin or into the immediate vicinity. For meaningful and sustained protection, the extracted and processed essential oil is necessary, not the plant itself.