Question:
What plants will repel mosquitos when planted nearby?Answer:
While several plants, such as scented geranium, lemon thyme, citronella grass, and "citrosa", are touted as mosquito repellents, they are ineffective. Some of these plants contain chemicals shown to have repellent properties (citronella grass produces the citronella oil used in mosquito-repelling candles, for example). These benefits are realized only when the plant is crushed to release its oils. A plant just sitting on the patio has no effect on mosquitoes in the area.
A pile of damaged leaves sitting on a table is not terribly effective either. The likely best way to use these plants as a repellent is to crush some leaves and rub the oil on your skin (checking to make sure you are not allergic first, of course). This will provide some benefit, but only at a fraction of the rate as products developed and used as repellents (such as DEET).
In short, using plants placed in the landscape as mosquito repellents does not work. Learn more in this article: Mosquito Control.