My ears have been fine-tuned to catch any references to natural ways to repel mosquitoes. Since the addition of four 50 gallon rain barrels to my yard and garden, it has been a constant battle to keep screens in place over the drainpipe openings and overflow exits, and Mosquito Dunks in all the barrels, to prevent the blood-thirsty little buggers from experiencing an unprecedented population boom.
Despite all my efforts, they seem to linger at every doorway and in every corner of my garden, just waiting for me to set foot out of my house. I keep DEET insect repellent near my back door, and have pondered the purchase of permethrin-infused clothing. Back in the early years of our marriage, nearly 20 years ago, my husband and I even drew smiles from our elderly neighbors for gardening late into the evening by the light of citronella tikki torches.
An acquaintance, a friend of a friend, mentioned that she had gotten rather carried away when she rooted cuttings of her citronella geraniums, and she didn't know what she was going to do with them all. She cast her eyes at the welts on my neck and arms (which I thought I was so surreptitiously scratching), and at the rain barrels standing sentry under my drain pipes, and asked if I wanted a few starts.
"They're called Mosquito Plant. The mosquitoes hate them! Plant them by your back door, and by where you grill out, and they'll leave you alone! You should try it!"
I was intrigued. I'd heard of citronella candles, of course, and citronella grass, but citronella geraniums were new to me.
"Just planting them in the ground repels the mosquitoes? You don't have to rub the leaves on your skin or make infusions of the oils or anything?" I asked. I have notoriously sensitive skin, and didn't relish the thought of doing yet another skin test on my inner elbow to see if I'd develop a blistering rash.
Her eyes darted away, and she mumbled, "Oh, well, that works, too. They smell so good when you rub your hands on the leaves! Do you want some?"
I have to confess, I'm a little bit of a skeptic. I love to share plants from my gardens, and regularly give away starts of plants that I'm dividing or moving, but I also have a well-formed kernel of caution down deep in my heart. When given a start of a plant, I always do my research to be sure it isn't invasive, or won't become a thug. Too often I've found that if someone has more of a plant than they know what to do with, that means it won't play nicely and stay where I've put it.
First, the good news. Citronella geranium, Pelargonium citrosum, is a tender perennial, so it can be grown either as an annual, or potted up and brought inside for the winter before the first hard frost hits. It is easy to grow in full sun or partial shade, and is fairly drought-resistant, though it does appreciate regular watering while it is getting established. It rarely requires fertilizer, though it does appreciate being cut back to promote a more bushy form. It doesn't spread or self-seed prolifically, growing to a height and spread of around 24 inches. It has deeply lobed, lacy leaves, and the eye-catching pink and magenta flowers alone make it worth growing. Like many scented geraniums, you have only to brush against the leaves, or rub them gently between your fingers, to release their fragrance. When I sniffed at the leaves, they did, indeed, have a pleasant, lemon-citrus smell that was very reminiscent of ubiquitous citronella candles of my childhood camping trips.
Bad news was soon to follow, however. The plant was developed in the late 1980's by a Dutch horticulturist, Dr. Dirk Van Leeni, who claimed it was a genetically engineered hybrid of an African rose-scented geranium (Pelargonium graveolens) and Chinese citronella grass (Cymbopogon nardus), which is the source of the citronella oil used in so many insect-repelling products. This was later exposed as a hoax. The plant was actually a scented geranium, with a fragrance that strongly resembled the familiar smell of citronella. The Herb Society of America publishes a Pelargoniums Guide in pdf format, which provides these telling details about the supposed mosquito-repelling citronella geranium: "The plant's oil composition was very similar to rose geranium, including only .09% citronellal (one of the active components in citronella oil). The citrosa plant did not protect human subjects from mosquito bites more than controls, and in one field trial mosquitoes actually landed on the plant."
A New York Times article from 1991, shortly after the public release of the highly-touted plant, also describes a preliminary study done to see if proximity to the plant would actually reduce the number of mosquito bites. Their results were disappointing, as well:
"Canadian scientists did a preliminary study at the University of Guelph in Ontario because there were so many inquiries from growers," said Carl Schreck, an entomologist with the United States Department of Agriculture's research service in Gainesville, Fla. "But they found that when they put their arms in a cage with the plant, the mosquitoes bit them just as readily as without the plant. The advertising is quite misleading, and there's no scientific data to back it up." 
It seems many people are only too happy to believe the claims that these attractive plants will dispel the clouds of mosquitoes that descend as soon as we set foot outside. A quick internet search will yield many sources that still promote the false information about the parentage and effectiveness of the plant, despite the scientific and anecdotal evidence to the contrary. Even true citronella grass, Cymbopogon nardus, must be applied to the skin to be effective as a repellent. Simply planting them around your deck or pool area won't discourage the mosquitoes from sampling the tempting array of humans gathered there. Lemon thyme (Thymus x citriodorus) and lemon balm (Melissa officinalis) are more effective as very mild natural mosquito repellents than the citronella geranium, and have the additional bonus of being perennial plants.
In the end, I didn't receive any of the offered plants. Perhaps she was slightly offended when I gently questioned the amazing mosquito-repelling abilities of the offered plants, or perhaps she really did run out because she'd offered them to too many people, as she explained the next time our paths crossed. In either case, I was sorry, both because I hate to give offense when someone extends a genuine offer, and because I would gladly have added this pretty little plant to my borders, on the merits of its scent and blossoms alone.
 American Herb Society Factsheet on Pelargoniums, found at: www.herbsociety.org/factsheets/pelargoniums_fact.pdf
 Raver, Anne. "Citronella Without the Flames," New York Times, July 25, 1991. Found at http://www.nytimes.com/1991/07/25/garden/citronella-without-the-flames.html
In order of appearance. Many thanks to the photographers who make their work available through Flickr Creative Commons and Dave's Garden Plant Files. Pictures have been used in accordance with the terms of usage of those respective sites. Click on the links in photo credits to see the original image.
Thumbnail image of citronella geraniums blossoms: Flickr Creative Commons, submitted by photographer Santi. Some rights reserved.
Mosquito: Flickr Creative Commons, submitted by photographer John Tann. Some rights reserved.
Close-up of bloom: Flickr Creative Commons, submitted by photographer Clint. Some rights reserved.
Plant with blossoms: Dave's Garden Plant Files, submitted by Dave's Garden member jenica, of Hobbs Farm and Greenery. Used with permission, all rights reserved.