The truth about “pest-repelling” plants

These bright flowers are super hearty — French and signet varieties can be planted throughout summer — and they are often used as a "companion plant" by gardeners. So, do they also ward off mosquitoes? Well, while the flowers have been found to have powerful insecticidal properties, there's not much evidence that just planting them around will ward off bugs. Some gardeners still claim their strong sent will keep flying pests away, while others claim their roots keep common garden insects from munching on your plants. But, unless they are turned into an actual pesticide, these flowers probably won't help anymore than a citronella candle.

Now, does basil keep pests away from you or other plants? Well, maybe! There’s not much in the way of studies to back up the claim some make about its strong scent warding off flying pests, but some gardening enthusiasts believe it still makes a great companion plant. The Farmer’s Almanac recommends planting it alongside vegetables to protect them from tomato hornworms (which go after more than just tomatoes) and other gardening experts believe they protect tomatoes from spider mites. Regardless of whether or not this herb wards off insects, it’s a great thing to keep on your deck or kitchen windowsill to spice up your cooking. Just be cautious about planting it in your cottage garden, as it’s not native to Ontario.

Another herb that smells great to us, but some theorize is abhorrent to insects, is rosemary. The Farmer’s Almanac says it can deter cabbage moths, which are detrimental to many edible plants. But what about mosquitoes, you ask? Well, much like basil, it’s probably not potent enough to keep them away. While many plants have some sort of bug-repelling properties, they don’t actually repel bugs unless certain compounds found in their petals or leaves are released or distilled. Even then, it's unclear how much of an effect this will really have. However, this probably explains why some people recommend burning rosemary, believing these compounds are released in their smoke. We were unable to find any scientific evidence to back this up—but we’re sure burning rosemary smells real nice!

This weed will bring all the cats to your yard! But will it keep pests out of it, you ask? Some studies have found that nepetalactone, the essential oil that gives catnip its signature kitty-enticing scent, is more effective than DEET. That doesn’t mean planting the stuff around your cottage will infuse the air with this mosquito-repelling oil. More importantly, catnip is a member of the mint family and considered a weed. Best to keep it out of your garden.

According to the Farmer's Almanac, fragrant lavender repels moths, flies, fleas, and mosquitoes. However, some scientists don't think it's quite up to snuff. Cheryl Ann Farr, a professor of textiles and clothing at Oklahoma State University, told the New York Times that there's little evidence the dried herb wards off moths. Much like the other herbs we've looked at, lavender may have some pesticide properties, but they won't create a mosquito-free space.

Geraniums provide a nice, bright pop of colour to decks and window boxes, and, if you crush the leaves between your fingers and rub them over your skin you may enjoy some all-natural pest control. However, you should definitely do a swatch test first by rubbing a small amount on your skin and waiting a day or so to make sure the compounds don't irritate your skin.

While we may hope that somewhere out there is an all-natural, non-toxic bug spray, "bug-repelling" plants seem to be more fiction than fact. While many plants have pesticide properties, planting them in your garden or on your deck is unlikely to result in a pest-free space. Plus, many of these plants aren't native to Canada in the first place, which is just one more reason not to buy into the myth.