Mosuito Plants - Or Maybe Not

Unless you're just back from a trip to Mars, you've no doubt seen the "citrosa" plant advertised in newspapers and magazines in the United States and Canada as "guaranteed to repel mosquitoes." The supplier claims the plant is a "unique genetic combination " of a scented geranium and citronella grass (which does produce the citronella oil used in mosquito-repelling candles and the like). Many of you have written to us asking if this good news could possibly be true.

Well, We're sorry to report that all the experts we've checked with say "no." In fact, Arthur Tucker, Ph.D.., plant fragrance specialist at Delaware State College in Dover, tells us that chemical analysis of this "miracle plant" revealed that it contains only 0.09 percent citronellal (one of the main ingredients in citronella oil). Some forms of lemon balm beat that by a factor of around 400 (38 percent citronellal), he points out.

"If you want to grow a plant that might help repel mosquitoes, there are several that would probably be better choices," Dr. Tucker says. He adds that G. A. Surgeoner, Ph.D., of the University of Guelph in Ontario compared a potted citrosa plant (just sitting there) and its crushed leaves to DEEP WOODS OFF (which contains the powerful chemical DEET, the active ingredient in most rub-on insect repellents) and found that the citrosa in a pot (as it is shown in the ads touting its alleged repellent powers) has no significant effect against mosquitoes.

Crushed citrosa leaves, however, do offer some protection - they have 30 to 40 percent of the repellency of DEET. But crushed lemon thyme (Thymus X citriodorus) has 62 percent! So lemon thyme should work better than the much-ballyhooed citrosa plant. Which is nice because thyme costs much less and is winter-hardy while the citros is not. (Lemon thyme is available from many herb suppliers, including Companion Plants, 7247 No Coolville Ridge Road, Athens, OH 45701; and Richter's, Goodwood, ONT, Canada LOC 1A0.

The important fact to remember is that no plant - citrosa, lemon thyme or even citronella grass itself (a very hard to find 6- foot-tall tropical plant) will repel skeeters just sitting in a pot. Plants release significant amounts of their repellent oils only when their leaves are crushed, Dr. Tucker says. If you want to go that route, rubbing the crushed leaves on your skin is probably the best way to use these sweet-smelling natural insect repellents. (Be sure and "patch test" yourself for any allergy to these leaves by testing a small amount repeatedly on your inner forearm for a day or so; if there's no irritating skin reaction or redness, it's likely safe for you to rub away!)

In the meantime, why not grow some mosquito repellent of your own? If you have a sunny, well-drained patch of lean garden soil, try planting some catnip. The plant you need is a perennial herb called Nepeta cataria. Closely related to ornamental catmint, or Nepeta faassenii (or N. mussinii), catnip is generally grown as a cat-pleasing or medicinal tea herb rather than for its looks.

Catnip is far from ugly, but its gentle blue flowers are definitely out-produced by its masses of softly hairy, gray-green foliage. Like most herbs, it prefers well-drained soil and plenty of sunlight. If you garden on heavy clay, you may succeed better with catnip and other herbs if you give them a mounded bed or grow them on a slope to improve winter drainage.

The first year you plant catnip, you may need to water it a time or two, especially if next summer is as hot and dry as this one has been. However, fall-planted herbs, including catnip, often need very little water the following summer. Fall and winter rains can help plants create deep, strong root systems that increase the natural drought resistance of catnip and many other herbs.

Don't feed your fall-planted herbs, but do mix some compost into their planting soil. A mix of half compost, half native soil is usually just right. Top off the soil with a light blanket of compost (2-3 inches) to help feed those actively growing roots through the cool months.

Even in spring, don't feed your herbs with anything but compost, or at most a mild all-purpose organic fertilizer such as Whitney Farms 5-5-5. Adding too much fertilizer can cause lush overgrowth in many herbs, leading to dilute or low-quality essential oil production. In some cases, herbs such as creeping thymes can be killed by commercial fertilizers, so when in doubt, use only a very mild fertilizer and apply it at half the suggested application rate.

This summer, I experimented with making both catnip vinegar spritzers and catnip infused oils. Both did a fine job of keeping mosquitoes and no-see-ums at bay during our warm summer evenings. If you would like to try this yourself, here are the simple recipes I used:

Mosquito Plant

The Mosquito Plant is a genetically engineered geranium hybrid with a unique characteristic: it repels mosquitoes! It is easily grown as a potted patio plant, and easily enjoyed for its attractive foliage and sweet lemony scent, as well as for its mosquito repelling powers. It produces a leafy, attractive, foot-tall plant during its first season.

The Mosquito Plant was created by a Dutch botanist, who genetically incorporated traits of the Chinese citronella grass into a scented African geranium. The resulting cultivar still had the growth and habit of the geranium, and its sweet lemony citronella scent. Citronella is the substance in citronella candles, which have long been used to deter mosquitoes. It doesn't harm them, but they don't like citronella and avoid it. It is most effective as a repellent if you crush a few leaves and rub them on your skin. This releases the citronella and a sweet perfume.

Like most geraniums, the Mosquito Plant is normally potted and grown outdoors during the warm season (after last and before first frosts). During the colder seasons the plants can be wintered-over indoors. In the warmer southern zones Mosquito Plants can be grown outdoors year-round where the plants can reach a mature size of 3 to 4 feet high and wide.

Planting and Care:

New plants can be potted in a 4-inch or larger pot. Or they can be grouped in a patio planter spaced a foot apart. Use any potting soil recommended for geraniums. Keep watered and occasionally feed with a soluble plant food, as you would any potted plant. Mosquito Plants like full sun, but do well in partial shade. In the fall, you can move the plants indoors to enjoy as houseplants, or winter them over with your other geraniums in a heated garage, near a window or under grow lights.

During the summer, put potted plants on patio tables and near lounges to keep mosquitoes at bay. For even more protection, crush and rub the leaves on your skin for a sweet, natural perfume that bugs mosquitoes.

I can still see the veil of foggy mist off in the distance and hear the rumble of the obese tanker truck as it slowly crept down our street seeking out its prey. Mom yelling from the house to get inside and friends scurrying away so as not to become covered with the dewy mix were nightly summer occurrences. Thinking all safe after the commotion passed, we would return to our innocent games on grass laden with freshly sprayed pesticide. It was called Mosquito Abatement. The funny thing was that there never seemed to be a shortage of mosquitoes. The year was 1964; the city was Houston.

It was during this period that my childhood pet Boxer, bitten by a mosquito he couldn't protect himself from and worked into a frenzy as my Mother sprayed him with toxic flea repellent he couldn't escape, fell down never to rise. Last summer we were told that one of our dogs had heartworms, a fairly new occurrence in our area brought by the mosquito. Fortunately, there are courses of treatment and preventative measures now, and our furry friend will be OK.

It is no wonder, though, that the mosquito is a hated foe. You are probably wondering what this has to do with plants. It has been more than a decade since the introduction of the so called Mosquito Plant. Anxious to arm themselves with whatever ammo might be available, consumers were more than ready to be told that there was a magic plant that, if just placed on the patio, would make our tiny winged enemy, the mosquito, turn and run. The plant was supposed to have been engineered by a Norwegian scientist, a Dr. So and So with a very impressive sounding name, and it was introduced by a well known and 'respectable' plant purveyor. A member of the Scented Geranium family, this plant was called the Citrosa Geranium, after Citronella oil. It showed up in Supermarkets, High End Catalog Companies and was even on the Home Shopping Network. The prices were high, but the promise of no more mosquitoes was a powerful marketing tool and the plants flew off the shelves.

It didn't take long for someone to start scrutinizing this plant and what they found was, at the time, really shocking. Not only was there no famous scientist, there was so little Citronella oil in the plant that even crushing it and rubbing it on the skin would do little to protect someone from the dreaded mosquito. Organic Gardening Magazine reported that Lemon Thyme had a much higher concentration of the needed chemical, Citronellol, and we all know that Lemon Thyme coexists peacefully with mosquitoes playing all around.