Citronella plants, typically sold as lemon-scented geraniums, do not repel mosquitoes. It is the oil within the leaves that contains the properties needed to repel mosquitoes. The leaves must be crushed or rubbed to extract the oil. Outside of the oil within the leaves, the plant itself has no mosquito-repelling qualities whatsoever.
In conclusion, when it comes to repelling mosquitoes, citronella oil is better than nothing, but it’s far from an effective solution. It’s best to pair the citronella oil with other mosquito deterrents, such as DEET or vanillin.