The popular belief that planting geraniums near a patio or window creates a mosquito-free zone is widespread among home gardeners. This assumption has led to the commercial marketing of plants as “mosquito-repelling” varieties. Investigating this claim requires separating botanical fact from marketing fiction and understanding how repellents work.
Clarifying the Geranium Confusion
The plants sold as “mosquito-repellent geraniums” are not true geraniums (Geranium genus). They are scented pelargoniums (Pelargonium genus), often called the Citrosa Geranium or Pelargonium citrosum.
This botanical mix-up is important because the plant’s perceived repellent property comes from its strong, citrus-like aroma. The scent is reminiscent of citronella, a known mosquito deterrent compound. However, the true source of citronella oil is citronella grass (Cymbopogon species), not any variety of pelargonium.
The Science of Repellency
The living Pelargonium plant contains volatile organic compounds (VOCs) like citronellol and geraniol, which interfere with a mosquito’s ability to detect humans. These compounds are stored in the leaves and are released only in small amounts when the foliage is crushed or brushed against. Since the plant must be damaged to release its active chemicals, it fails to create a protective vapor barrier just by existing in a pot.
Scientific studies testing the efficacy of the intact, living plant consistently find it provides minimal to no protection against mosquito bites. Researchers have observed mosquitoes landing and resting directly on the leaves, suggesting a lack of repellency in a natural setting. The concentration of airborne compounds is too low to deter mosquitoes from nearby human hosts.
The chemical compounds, such as geraniol, are effective when extracted and concentrated into oils or diffusers. This distinction between the potency of the extracted compound and the ineffectiveness of the natural delivery system explains why the popular geranium claim is false.
Effective Alternatives for Mosquito Control
Since relying on a potted plant for protection is ineffective, adopting scientifically validated methods is the most reliable strategy for mosquito control. Eliminating sources of standing water (bird baths, clogged gutters, old tires) is a fundamental physical defense, as mosquitoes breed in still water. Installing or repairing window and door screens also prevents mosquitoes from entering living spaces.
For personal protection, chemical repellents approved by regulatory agencies offer the best defense. The most reliable active ingredients include:
- DEET, recommended in concentrations between 7 and 30 percent for effective protection.
- Picaridin, a synthetic compound resembling a natural pepper extract, typically used at 10 to 20 percent concentration.
- Oil of Lemon Eucalyptus (OLE), the only natural ingredient with federal approval and public health recommendations. OLE (or its synthetic derivative PMD) is typically found in 30 to 40 percent concentration and provides protection comparable to lower concentrations of DEET.
Applying a portable fan to an outdoor sitting area can also disrupt a mosquito’s flight path.