Stone, I've kept Citronella (4" potted plants) in the yard. It works, IF you're sitting right next to it..LOL..
They smell too much like Raid, an odor I'd rather not breath, so I don't care for them. It's probably safe though. Safer than breathing Raid in the can.
On the other hand, people on the Hoya forum vow Citronella and other fragrant Geraniums, (dried and crushed) keep Mealy away..
A good-sized Citronella works..I used to work in a plant store, and someone gave me a free 4' Citronella tree..I hated its smell, gave it away..The tree was in the front yard, about 8' from the porch..While sitting out front, I have to say the smell kept mosquitos away. So, IMO, if you have a large tree or several smaller plants, it'd probably do the job..Toni

There is an active Mosquito Repellent Plants thread that you might be interested in reading. I would add that mosquitoes breed and multiply in water. These mosquitoes ideal environment around the home must be dealt with to reduce the chance of their bite.

{{gwi:68416}}

There was a severe drought here last summer, but I had two potted citronella plants on the porch (that I neglected sadly, I'm horrified to admit). They're real survivors. I don't know if I had a mosquito bite all summer long, and I spend a LOT of time on that porch at dusk and into the night (cool down with a frosty one after a hard day, ya know). Was it the plants?...the drought?....my natural muskiness after working in the garden all day?...who knows?

Citronella geraniums are so prolific I can't seem to keep them from propagating on their own. I have many in my yard, and have exported some to our church property. I have nearly no mosquitoes in the summer, but whether citronella is alone responsible, I'm not sure, as I also have lavender, rosemary, oregano, and thyme, all fragrant and thus insect repelling...

I bought an abused citronella plant from Lowes Last year and kept it alive in my bathroom over the winter ( since I don't know its hardiness) It's outside now and growing in the pot. But when I saw my cat being swarmed by mosquitoes, I rubbed some of the leaves with my hand and then rubbed down my cat from head to tail and now the mosquitoes are not swarming her anymore. I'd love to know how to get it to grow or drop seed or however they spread and propagate cause my backyard jungle is a swamp full of mosquitoes. there is a city drain pipe that ends in MY BACK YARD so there is nothing I can do about it.