The idea of planting lemongrass (Cymbopogon species) as a natural barrier against mosquitoes is a popular piece of folk wisdom. This tropical grass, recognized by its long, slender blades and sharp, citrus-like aroma, is widely cultivated for culinary and aromatic uses. Many people attempt to use the living plant to create a mosquito-free zone around their patios and homes, believing the plant’s strong scent alone is sufficient to repel biting insects. This raises a straightforward question: Does simply having an intact lemongrass plant provide a reliable shield against mosquitoes?
Identifying the Repellent Compound
The scientific basis for lemongrass’s reputation as an insect deterrent lies in the volatile organic compounds (VOCs) contained within its tissues. These aromatic molecules serve as the plant’s natural defense mechanism against herbivores and insects. The primary compounds in lemongrass (Cymbopogon citratus) responsible for this repellent action are neral and geranial, which together form citral. Citral interferes with a mosquito’s ability to detect the carbon dioxide and lactic acid humans exhale, effectively masking the host.
A closely related and highly effective compound, citronellal, is also present in other Cymbopogon species, particularly citronella grass, which is the source of commercial citronella oil. Both citral and citronellal are aldehydes that possess a powerful, lemon-like scent mosquitoes find highly disagreeable. These potent chemical components are concentrated in the plant’s essential oil. This oil has historically been extracted and used in commercial repellent products, such as candles and topical lotions, creating a localized, highly concentrated vapor barrier that deters mosquitoes.
The Limitations of the Intact Plant
The reason a living lemongrass plant offers negligible protection is directly related to how the repellent compounds are stored and released. The plant produces and retains these VOCs, such as citral, in specialized oil glands located within the leaf and stem structure. These compounds are not continuously released into the atmosphere in large quantities. The plant must be physically damaged or processed for the oil glands to rupture and liberate the concentrated molecules.
A healthy, intact plant releases only a minuscule amount of these volatile compounds through passive emission. This minor release is insufficient to create a protective cloud or vapor barrier large enough to cover a person or a small outdoor seating area. Studies consistently show that the passive release of VOCs does not reach the necessary concentration to effectively deter mosquitoes. The concentration of citral in the air immediately surrounding the plant remains too low to confuse or repel the insects.
Therefore, the plant’s strong scent, which is noticeable to humans, does not translate to a functional deterrent for mosquitoes unless the leaf tissues are broken. The idea that a single plant or a row of plants can establish a perimeter of protection is a misunderstanding of the biological mechanism. Simply placing the plant on a patio table provides little more than a pleasant aroma until the leaves are actively manipulated.
Optimal Methods for Utilizing Lemongrass
For lemongrass to function as an effective mosquito repellent, its volatile compounds must be actively released and concentrated. One immediate, low-tech method involves manually crushing or bruising the fresh leaves and stems. This mechanical action breaks the oil glands and allows the repellent compounds to vaporize into the air at a higher concentration. Rubbing the crushed leaves directly onto exposed skin is a traditional method that transfers the concentrated oil, creating a temporary, localized repellent layer.
A more sophisticated approach involves extracting and concentrating the essential oil for use in various products. Steam distillation of lemongrass yields an oil rich in citral, which can then be incorporated into topical solutions, sprays, or candles. When using the processed essential oil, it must be properly diluted with a carrier oil before being applied to the skin to avoid irritation. Due to the volatility of citral and citronellal, any application requires frequent reapplication, typically every few hours, to maintain the necessary concentration. Burning candles or using diffusers releases a plume of concentrated vapor that creates a temporary, localized zone of protection.