Mosquito repellent plants - fact or fiction?

Last year we published an article on the most common plants that allegedly repel mosquitoes.

Now that we’re into the mosquito season and we’d like to enjoy family time outdoors, repelling mosquitoes is on all of our minds. None of us likes chemical-smelling mosquito repellents, so it’s appealing to think about plantings that repel mosquitoes. We’ve all heard of “Mosquito Plants”, hyped as having the ability to drive mosquitoes away. Indeed, there are plants that mosquitoes don’t like. Citronella is the best known. A tall grass native to climates with no frost, Citronella won’t survive winter in Ohio.

A better choice is Bee Balm (Monarda or Horsemint), an adaptable perennial that repels mosquitoes much the same as citronella. It gives off a strong incense-like odor which confuses mosquitoes by masking the smell of its usual hosts.

Another mosquito repellant plant is the Marigold, commonly grown as an ornamental border plant. Marigolds contain Pyrethrum, a compound used in many insect repellents, and have a distinctive smell that mosquitoes dislike. If they are positioned near mosquito entry points such as open windows, the smell may deter mosquitoes from going past this barrier.

Ageratum, also known as Flossflower, also emits a smell that mosquitoes find offensive. Ageratum secretes coumarin, widely used in commercial mosquito repellents.

Catnip is a natural mosquito repellent. Entomologists at Iowa State University report that catnip is ten times more effective than DEET, the chemical found in most commercial insect repellents. In comparison tests, a ten-fold higher concentration of DEET was required to obtain results similar to those of Catnip.

You’ve probably seen “Citrosa” plants advertised as “guaranteed to repel mosquitoes.” Suppliers claim the plants are a “unique genetic combination” of scented geranium and citronella grass. We’re sorry to report that Arthur Tucker, Ph.D., plant fragrance specialist at Delaware State College, says this “miracle plant” contains only 0.09 percent citronella. “If you want to grow a plant that might help repel mosquitoes, there are several that would probably be better choices,” Dr. Tucker says. He adds that G. A. Surgeoner, Ph.D., of the University of Guelph in Ontario, found that Citrosa in a pot (as it is shown in the ads) has no significant effect against mosquitoes.

The fact is that no plant – Citrosa, catnip or even citronella grass itself (a very hard to find 6- foot-tall tropical plant) will repel mosquitoes just sitting in a pot. Plants release significant amounts of their repellent oils only when their leaves are crushed. Rubbing the crushed leaves on your skin is the only really effective way to use these sweet-smelling natural insect repellents.

Citronella is the most common natural ingredient used in formulating mosquito repellents. The distinctive citronella aroma is a strong smell which masks other attractants to mosquitoes, making it harder for them to find you. Most outdoor products on the retail market contain less than 2% essential oils, far less than needed to be effectively aromatic.

Citronella candles and incense sticks are only effective if the air is still enough for their scent to linger in your outdoor living area. If there is a breeze, rubbing or spraying repellent on your clothes or skin will work better.

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