Many people believe that certain garden plants, commonly called geraniums, can deter mosquitoes from outdoor spaces. This idea appeals to those seeking natural alternatives to synthetic chemical repellents. However, the true effectiveness of this natural pest control depends heavily on the specific plant and how its aromatic compounds are utilized.
The Identity Crisis: Geraniums Versus Scented Pelargoniums
The plant most people associate with mosquito-repelling properties is not a true geranium. The common garden flower belongs to the genus Geranium, which is taxonomically distinct from the scented variety often marketed as the “Mosquito Plant.” This aromatic plant is a type of scented geranium, classified under the genus Pelargonium. Botanists later separated these genera based on flower structure and other characteristics.
The specific cultivar frequently sold for its supposed repellent qualities is typically Pelargonium citrosum ‘Mosquito Plant’ or a similar hybrid. This plant is sometimes misleadingly labeled a “Citrosa Geranium” or “Citronella Geranium,” implying a connection to true citronella grass (Cymbopogon species). The confusion is compounded because the plant’s foliage, when crushed, releases a strong, lemony scent reminiscent of citronella.
The repellent properties are tied to the volatile oils within the leaves of the Pelargonium genus. Scientific studies show that Pelargonium citrosum, despite its reputation, is largely ineffective at repelling mosquitoes when simply growing in a pot. Researchers have observed mosquitoes landing directly on the leaves during field evaluations, demonstrating a lack of passive repellency. This suggests the mere presence of the growing plant does not release enough active chemical compounds to create a protective barrier.
The Active Ingredient: Geraniol and Citronellal
The mechanism behind the plant’s potential repellency is found in the volatile organic compounds (VOCs) contained in its essential oils. The two primary compounds associated with the scent of these plants and other natural repellents are Geraniol and Citronellal. These chemicals are released into the air and work by interfering with a mosquito’s olfactory system, which is the insect’s primary tool for locating a host.
Mosquitoes are drawn to the carbon dioxide and specific body odors we emit, and these VOCs act as an olfactory mask. By disrupting the mosquito’s ability to sense these attractants, the compounds temporarily confuse the insect and prevent it from landing. Geraniol, a monoterpene alcohol, is a component of geranium oil and has been shown in studies to exhibit strong repellent activity.
Scientific data indicates that Geraniol is superior to Citronellal in terms of both the intensity and duration of its repellent effect. For example, mechanical diffusers using Geraniol have demonstrated a significantly higher repellency rate against mosquitoes compared to those using Citronellal in both indoor and outdoor settings. While the specific Pelargonium variety contains only trace amounts of Citronellal, the presence of Geraniol contributes to the plant’s overall aromatic profile.
Limitations of Passive Repellency and Practical Use
The primary limitation of using the “Mosquito Plant” for pest control is the difference between passive and active use. A whole, growing plant does not naturally emit a sufficient concentration of its VOCs into the surrounding air to create an effective protective barrier. The repellent compounds are not volatile enough when the plant is undisturbed to deter mosquitoes over a wide area.
For the repellent chemicals to be released in any meaningful quantity, the plant’s leaves must be physically disturbed or crushed. This action breaks the plant’s oil glands, releasing the concentrated essential oils onto the skin or into the immediate vicinity. Therefore, relying on the plant simply sitting in a pot or garden bed will likely yield no noticeable reduction in mosquito bites.
To maximize the natural repellent effect, the scented foliage needs to be actively utilized.
Methods for Active Use
One practical method is to rub the crushed leaves directly onto exposed skin or clothing before spending time outdoors. This transfers the oils containing Geraniol and Citronellal, creating a temporary, localized repellent layer. Alternatively, placing the plant pots in high-traffic areas, such as near a seating area, and brushing against them occasionally can release a small burst of scent.
Even with active use, the protection time of the plant’s raw oil is short due to the high volatility of the compounds, requiring frequent reapplication for sustained effectiveness.