We wish this was true!
Over the last few years, we have been repeatedly asked for certain plants that have been touted as being able to repel mosquitoes. With the general notion that simply planting these will stop mosquitoes from entering your yard. I have many of these plants in my yard and still have mosquitoes (what got rid of them, was turning over a full container of water, in my neighbors side yard). If this were true, it would have been common knowledge, long before it hit the internet. Mosquitoes may not choose to land on “those” plants, but having “those” plants in your yard, won’t stop them from landing on you. Plants have been used for millennia to deter pests, some work better than others and most are insect specific. It is not the plant that repels insects, but a chemical in the plant that works.
Google is so handy!
I am one of those critical skeptics. I Googled “plants that repel mosquitoes” and got 800,000 + hits. I had to read down through 8 pages, before I found an article about a study at the University of Guelph in Ontario, that refutes the mosquito repelling properties of Citronella plant (Pelargonium citrosum), which is a citronella scented geranium. https://byf.unl.edu/Citronella
When I Googled “plant-based mosquito repellents” I got 144,000 hits. Most were companies advertising their “natural” products. The 1st hit was this one, about the 4 most commonly used ingredients in “natural” mosquito repellents. https://www.pesticide.org/Alternatives/home-and-garden-toolbox/pest-solutions/plant-based-mosquito-repellents
The second hit was the kind of thing, I was really looking for. This is, where I suspect, this whole thing started. I think many people reading this review, didn’t understand it, read too much into it or they could have chosen to ignore Table 1. This a scientific review, published in 2011. The review sites 111 other studies, papers, articles, charts and tables. Parts of this are not an easy read, but worth doing. I found the tables most interesting.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3059459/
Unfortunately, very few whole living plants were cited, most of the studies are for extracts and oils that were burned in oil lamps or applied directly to the skin. In others studies, the plant or leaves were burned. The plants listed in Table 1, contain many species we are familiar with, but the varieties are different from the ones we commonly see available here. For instance, Tagetes minuta is on Table 1. This is a type of marigold with tiny flowers and can reportedly get up to 10 foot tall (yikes). In California it’s considered a CDFA class A noxious weed, each plant producing tens on thousands of seeds. The lists of mosquito repelling plants, on the internet and in print, show pictures or name French Marigolds (Tagetes patula), Mexican Marigold Mint (Tagetes lucida), Copper Canyon Daisy (tagetes lemonii) or African Marigolds (Tagetes erecta). In the study cited, Tagetes minuta was applied topically (to the skin) or the fresh leaves were scattered in door ways, and “reduced human landings indoors”. No scientist worth a federal grant would make the assumption that you can replace one variety for another and expect a similar outcome. The same scientists wouldn’t assume that having plants in the yard could recreate the findings either.
It basically says that some chemicals in plants, do repel mosquitoes, to some extent. But, you would need to extract the chemical from the plant. This is so simple, that it could be done in any high school lab. Then mix it in the right concentration, with the right additives, apply it to yourself and hope that you don’t have a reaction (see Table 2), then reapply often. This review also states that there are just are not enough studies to conclude positively that the natural extracts in question work better, or are safer, than the chemicals people are trying to avoid.
I dug around the internet…a lot…and couldn’t find any scientific paper, review, study, article, or thesis that can back up the claims that having “those” plants, in your garden, will keep mosquitos out of your yard. The review above is cited over a hundred of times on other sites, in several languages.
Other reading
The EPA calls a chemical derived from a plant a biochemical. Biochemicals require less testing…why should they get preferential treatment…arsenic and mercury are “natural”. If you’re interested in further reading about testing and effects of biochemicals, try this Biopesticide Re-registration Eligibility Document. It’s for p-Menthane-3,8-diol, which is derived from Eucalyptus. Yet it’s synthesized chemically in a lab for quick, large-scale production…does that count as natural? Most of it is technical, but hey, we all need a challenge.
https://www.epa.gov/opp00001/chem_search/reg_actions/registration/related_PC-011550_1-May-00.pdf
This product will be up for review, next year. These types of documents are available for public review. This particular document is a good example, but you can read about any product out there.
A challenge!
Simply having “those” plants in your yard, will not repel mosquitoes (except from landing on the plant). You could try planting your yard solid with them and lay down in between the plants…it’s just hard to keep an eye on the barbecue from that position. Using extracts and oils from “those” plants, will work to deter mosquitoes to varying degrees. The difference between extracts or oils from plants and the entire plant, can be compared to beef broth and the entire cow…having a cow in your kitchen will not make your soup better. I tried cutting fresh basil and rubbing it on my arms and legs. It didn’t make the mosquitoes stop biting me, but I did get a craving for pesto. Another day, I tried mint, still got bit and that made me want gum. When I tried lemon thyme, I stuck some fresh sprigs in the top of my socks. The sprigs kept falling out (which was annoying) and irritated my skin. Now, if you figure out a method of strapping these “mosquito repelling” plants to your ankles and not get dirt in your socks, let me know.