Mosquito Plants

There are many herbal preparations that claim to keep mosquitoes away but how effective are they? The gold standard of mosquito repellants is DEET, a chemical many people want to avoid. There are some plants that do have mosquito repellant properties and in this article we will discuss them.

First of all there are no plants that you can just sit on the patio or plant around the house that will effectively repel mosquitoes, despite all those advertising claims. No objective studies have ever found a plant that will do that. The chemicals that repel insects must be extracted from the plants in some way and applied to the skin. Even burning the chemicals in a candle or as incense has little effect. Most studies find that burning a plain candle is just as effective as burning a citronella one.

Citronella
True citronella really does repel mosquitoes quite effectively. It is a rangy, rough grass like plant that grows in tropical areas. If you can find the plant for sale, northern gardeners can grow it in pots. In the far south citronella has escaped cultivation and may become a pest. It can grow up to 6 feet tall. Citronella is cultivated in several areas of the world and the oil distilled from it is processed into a variety of products.

Fresh citronella oil has a somewhat lemony scent. The active ingredient in citronella oil that repels insects is citronellol. Many other plants also contain this chemical in lesser amounts. In several studies a 10% solution of citronellol was almost as effective as DEET in repelling mosquitoes- for 15 minutes.

That is the problem with using citronella as an insect repellent. It must be used in a very strong concentration and the effect wears off quickly. Citronella is only effective if applied to the skin. That causes another problem, many people are allergic to strong concentrations or their skin becomes irritated. Citronella oil is absorbed through the skin and some studies are linking exposure to the chemical to liver damage and cancer.

Most citronella products you buy at the store are so diluted that they contain almost no active ingredient. It is a waste of money to buy citronella oil or candles to burn unless you just like the smell. There are some good, herbal preparations for repelling mosquitoes that include citronella in their ingredients but all must be applied frequently.

Citrosa, Mosquito Plant
The citrosa plant (Pelargonium citrosum -van Leenii') sometimes advertised as Mosquito plant, Mosquito Shoo, and other assorted names, is useless as a mosquito repellant. No plant repels mosquitoes just by sitting near you. This plant is actually a scented leaved geranium and it does have a very small amount of citronellol in it just as many other plants do. You would have to crush the leaves and rub them on your skin for it to have the most fleeting effect.

Thousands of these plants are sold each year, even though they don't work and don't even have a pretty flower or form to redeem them. Common Lemon Balm has 3-4 hundred percent more citronellol than Citrosa.

Geraniol
Geraniol is not a plant but a chemical found in many plants, including citronella, lemon grass, roses, geraniums etc. It is used as a fragrance and as a flavoring ingredient in a number of products. Experiments at the University of Florida found it quite effective at repelling mosquitoes. The problem is once again, that it causes skin irritation and it also irritates the eyes.

Soybean Oil
Surprisingly enough, soybean oil is a pretty effective insect repellent and doesn't cause the skin irritation like some other chemicals do. The effects do not last as long as Deet. It stains clothes and feels "greasy" so some people object to it. Some soybean oil based products are now on the market. If I were going to make my own mosquito repellent I would start with a soybean oil base.

Other Plants with Insect Repellant Properties
Some plants have chemical ingredients that when extracted, do have mosquito repellant properties. The problem is that the active ingredients are costly and hard to extract or they have some serious side effects. A chemical found in mints for example, is effective as an insect repellant but some studies have found kidney damage and genetic damage when it is used. Lemon Balm, Lemon Thyme, Catnip, Agastache, Marigolds, Rosemary, and coconut oil have also been found to repel insects to some extent.

A mixture of several essential oils from the plants listed above and some soybean oil might make a fairly effective insect repellent. You would need to apply it frequently. Before using it on large areas of the body I would try it on a small area to test for an allergic reaction or irritation. There are several "natural" insecticides now on the market that vary in effectiveness.

Other Ways to Control Mosquitoes
Keeping the grass and vegetation around the home trimmed and emptying all places where water could stand and allow mosquitoes to breed, reduces the population. All water that can't be emptied should be treated with BT, a naturally occurring bacteria that kills mosquito larvae and is harmless to humans and animals. It comes in floating briquettes or granules to use on large areas of water.

Other things that do not work to control mosquitoes are ultrasonic devices and light traps. Some traps using carbon dioxide and pheromones show promise but are expensive and each trap appeals to different species of the hundreds of mosquito species in the US.

Deet is the most studied insecticide in the world and has been used for over 40 years. It is a synthetic chemical product but if label directions are followed it is extremely safe. Since mosquitoes can carry deadly diseases, keeping them from biting you is extremely important.