As the outdoor season approaches, many homeowners and outdoor enthusiasts look for ways to control mosquitoes. With all the publicity about the West Nile virus, mosquito repelling products are gaining in popularity. But many commercial insect repellents contain from 5% to 25% DEET. There are concerns about the potential toxic effects of DEET, especially when used by children. Children who absorb high amounts of DEET through insect repellents have developed seizures, slurred speech, hypotension and bradycardia.
There are new DEET-free mosquito repellents on the market today which offer some relief to those venturing outdoors in mosquito season. But there are also certain plants which are easy to grow and will have some effect in repelling mosquitoes from areas of your home and garden.
Commonly grown as ornamental border plants, marigolds are hardy annual plants which have a distinctive smell which mosquitoes, and some gardeners, find particularly offensive. Marigolds contain Pyrethrum, a compound used in many insect repellents.
Marigolds prefer full sunlight and reasonably fertile soil. Although marigolds can be planted from seed, starter plants are inexpensive and readily available at most garden centers. Although an annual, marigold will often reseed itself in favourable conditions, or the gardener can easily collect seeds for future germination. Established plants will need to be thinned, and flowers should be dead-headed to promote additional blooms.
Potted marigolds can be positioned near entrances to your home and any common mosquito entry points, such as open windows. The smell may deter mosquitoes from going past this barrier. While marigolds can be used as border plants around the patio, we do not advise putting marigolds on the patio table since the bright blooms may attract wasps.
Besides repelling mosquitoes, marigolds repel insects which prey on tomato plants, so you may want to plant a few marigolds in your tomato bed for added protection.
Catnip is a natural mosquito repellent. In August 2010, entomologists at Iowa State University reported to the American Chemical Society that catnip is ten times more effective than DEET, the chemical found in most commercial insect repellents. According to Iowa State researcher Chris Peterson, the reason for its effectiveness is still unknown. “It might simply be acting as an irritant or they don’t like the smell. But nobody really knows why insect repellents work.”
In the laboratory, Peterson put groups of 20 mosquitoes in a two-foot glass tube, half of which was treated with nepetalactone, a biologically active characteristic constituent of catnip. After 10 minutes, only an average of 20 percent – about four mosquitoes – remained on the side of the tube treated with a high dose (1.0%) of the oil. In the low dose test (0.1%) an average of 25% – five mosquitoes – stayed on the treated side. When the same tests were conducted using DEET (diethyl-meta-toluamide), approximately 40 to 45% – eight to nine mosquitoes – remained on the treated side. A ten-fold higher concentration of DEET was required to obtain results similar to those of the Catnip.
Catnip, Nepeta cateria, is very easy to grow. This perennial herb is related to mint, and grows readily both as a weed and a commercially cultivated plant in most areas of the US.
While catnip will repel mosquitoes in close proximity to the plant, some people apply crushed catnip leaves or catnip oil for more robust protection. Bear in mind, however, that cats will respond to you similarly as they would respond to the plant itself. Cat owners may want to choose an alternative plant for repelling mosquitoes.
While the plants mentioned in this article have been shown to have mosquito-repelling properties, there are environmental variables that can mitigate their effectiveness. A breeze may direct odors in the opposite direction if advancing mosquitoes, reducing the plant’s effectiveness.New formulations of non-toxic mosquito repellents are commercially available, and are advised for people who want to enjoy the outdoors without the annoyance of persistent mosquitoes.
Also known as Beebalm, Horsemint is an adaptable perennial plant which repels mosquitoes much the same as citronella. It gives off a strong incense-like odor which confuses mosquitoes by masking the smell of its usual hosts.
Horsemint is a fast growing, shade-tolerant and drought-resistant plant which reaches a height and width of 2 – 3 feet. It does well in dry, sandy soil and can tolerate salty conditions, which is why it is often found in coastal and beach areas. Horsemint seeds can be sown indoors in trays for later transplanting, or sown directly into the ground in late summer in colder climate zones. Midwest and Eastern growing zones are favoured for growing horsemint.
Mature horsemint plants can be divided in spring and fall by dividing into small sections and transplanting into permanent locations. Horsemint can also be planted in pots for moving indoors in cold climate zones.
Horsemint leaves can be dried and used to make herbal tea. Its flowers will also attract bees and butterflies to your garden.