The unusually wet summer we’re having is a boon for mosquitoes. During seasons when we’d like to enjoy ourselves outdoors, repelling mosquitoes is on all 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, however the name Citronella is widely used for two very different plants; Citronella grass (also called Lemongrass), and a variety of scented Geranium with a lemony fragrance (Pelargonium citriodorum).
Citronella grass won’t survive winter in Ohio. A tall grass native to climates with no frost, it is widely grown as a source for citronella oil extract, the most common natural ingredient used in formulating mosquito repellents. The distinctive citronella aroma is a strong smell which masks your own body odor, making it harder for mosquitos to find you.
Lemon-scented Geranium isn’t a hardy perennial in Ohio either. You’ve probably seen this plant advertised as the “Citrosa plant” or even the “Mosquito Plant”, a “unique genetic combination” of scented geranium and citronella grass guaranteed to repel mosquitoes. 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 will repel mosquitoes just sitting in a pot or growing in your flower garden. 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 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.
Still, it may be worthwhile to grow insect-repelling plants if they are hardy and attractive. A good choice is Bee Balm (Monarda or Horsemint), an adaptable perennial with a citronella-like scent. It gives off a strong incense-like odor which confuses mosquitoes by masking the smell of its usual hosts. Ageratum, also known as floss flower, also emits a smell that mosquitoes find offensive. Ageratum secretes coumarin, widely used in commercial mosquito repellents. Another mosquito repellant plant is the Marigold, commonly grown as an annual 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 might deter mosquitoes from going past this barrier. 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 Catnip. Nepeta faasseneii, a cousin of Catnip commonly called Catmint, is one of our favorite garden perennials.
There are plenty of attractive, hardy flowering perennials that will enhance your landscape and may have some benefit as mosquito repellents. Actual Citronella isn’t one of them.
Steve Boehme is a landscape designer/installer specializing in outdoor living spaces. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.