Mosquitoes are a pain for every gardener, and over the years a number of plants have been recommended to repel mosquitoes. Almost all of these plants are fragrant and include such things as catnip, citronella grass, beebalm, marigolds, lemon balm, lavender, geraniums, thyme, wormwood, rosemary and various mints. If you plant these in your garden you will have less mosquitoes – or so the proponents claim.
Will plants growing in your garden or on your deck keep mosquitoes away?
Why Fragrant Plants?
Why is it that all of the recommended plants are fragrant?
One can only guess at how these legends get started, but we do know that mosquitoes can smell us. They can sense the presence of various chemicals in the air and they can even smell the carbon dioxide you breath out from 50 meters (150 ft) away.
Deet, the most common mosquito repellent, is also fragrant. I think we have conditioned to think that to be effective a mosquito repellent needs to be fragrant.
Consider this – mosquitoes can smell or sense carbon dioxide that is completely non-fragrant to humans. Maybe we should be looking at non-fragrant plants to repel mosquitoes?
Do Fragrant Plants Repel Mosquitoes?
The citronella plant, also called citronella grass, does not repel mosquitoes. It gives off very low levels of fragrance which have little or no effect on mosquitoes.
The mosquito plant, Pelargonium citrosum, has been tested on human subjects, as reported in Mosquito Plant, Pelargonium Citrosum – The Citrosa Plant , and it has no effect on mosquitoes even though it is quite fragrant.
There are reports that there are fewer mosquitoes in eucalyptus groves – but most of us can’t grow these. Some reports have looked at plants that are used in Africa, reference 2, as natural mosquito repelling plants, but none of the plants reported include the fragrant ones on the above list and testing was done inside experimental huts.
I found no scientific studies that looked at the repellency of garden plants. Many web sites list plants that repel mosquitoes, but none provide a reference to their source of information. Dr. Tucker, a fragrance expert (ref 3) stated that “plants release significant amounts of their repellent oils only when their leaves are crushed . The important fact to remember is that no plant – citrosa, lemon thyme or even citronella grass itself will repel skeeters just sitting in a pot.”
Except for anecdotal stories, I have found no evidence that garden variety plants repel mosquitoes to any significant degree. The one plant that was specifically marketed for the job, mosquito plant, Pelargonium citrosum, was tested and found not to work.
Extracts from a number of fragrant plants have been tested and several do repel mosquitoes. But this is only after the active ingredients are concentrated and applied directly to the skin. The effectiveness of most extracts that work is short lived to 2 hours or less. In comparison, low concentrations of DEET are effective for 6-8 hours.
The fact that concentrated plant extracts, when applied to the skin, repel mosquitoes does not mean the plants will have the same effect.
For more details on natural plant repellents have a look at Mosquito Repellents – Best Options.
Do Plants Repel Mosquitoes?
It is very likely that some smells from plants affect mosquitoes. However, the concentration of such odors are very low and therefore have a limited effect. It seems highly unlikely that a plant 5 feet away, or sitting beside you on a patio will keep mosquitoes away.
If you feel this conclusion is incorrect, please post a reference that contradicts this conclusion. Don’t just tell me that the plants work for you. Find me a scientific study that shows plants repel mosquitoes.
What Does Work for Mosquitoes?
You will see from the above list that most mosquito repelling devices either don’t work, or work in a very limited way. So how do you keep mosquitoes from biting?
DEET and Picaridin are still your best choice for both safety and efficacy.
Here are some other posts that might interest you.
1) Fragrant Mosquito Repellents: http://www.huffingtonpost.com/2012/05/29/fragrant-mosquito-repellants-mint-chocolate_n_1553496.html
2) Repellency of Live Potted Plants Against Anopheles Gambiae From Human Baits in Semi-field Experimental Huts: http://www.ajtmh.org/content/67/2/191.short
3) Mosquito Repellent Plants: http://www.ipm.iastate.edu/ipm/hortnews/1993/5-26-1993/plant.html
3) Photo Source: Sanofi Pasteur