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Keeping Miserable Mosquitoes Away from Outdoor Areas


Q. What can I use in my yard to control mosquitoes? When it rains the lawn in the back stays damp, and I guess that's what attracts them. Thanks,
    ---Debbie in Aberdeen, Maryland
I installed a patio in a shady corner of my yard, and now I'm overwhelmed with mosquitoes assaulting me during their prime time of early evening—which is also my prime relaxing time! There is no standing water nearby. I just read your warning about rain gutters being a hidden breeding ground, but the mosquitoes are really only prominent in my patio area, not other places near the house/gutters. Could they be breeding in damp grassy areas nearby? And if so, can I spray with BTI to control them?
    ---Elaine in Narberth, PA
A. Mosquitoes can and do breed in grassy areas that stay wet—but so do wonderful and beneficial lightning bugs, so I appreciate that you're already suggesting a skeeter-specific method of control that's non-toxic to other low-to-the-ground creatures. Yes, BTI—a naturally occurring soil organism that prevents the successful march to adulthood of all biting flies that breed in water—is a very intelligent choice here. (For those of you now scratching your heads, mosquitoes are technically in the fly family. It's a big family!)

But I wouldn't spray it. In addition to the familiar donut-shaped BTI 'dunks' that are ubiquitous in hardware and home stores this time of year, BTI is also available in granular form. I personally use the granules in wet spots around my house to prevent mosquito, gnat, and blackfly breeding without harming toads or the wonderful 'glowworm' lightning bug larva down there. (Despite their common names of FireFLY and lightning bug, these flashing wonders are actually beetles, and unaffected by BTI.)

And don't neglect 'mechanical' control. One very effective way to keep mosquitoes—and no-see-ums, gnats and other small flying biters—out of an outside area is with a big fan blowing them away. It'll also help keep you a little cooler. Just make sure it's plugged into an outlet equipped with a Ground Fault Interrupter (GFI) for safety.

Q. Do mosquito repellents made from garlic really work? I've seen them advertised at my local green building supply store and online. Can you tell me anything about the one called "Mosquito Barrier?"
    ---Krystal in Ashburn, VA
A. I've had very good results with outdoor garlic sprays. There are many brands out there; the one you specifically mention, "Mosquito Barrier," may have been the first garlic oil-based spray marketed as a non-toxic mosquito fogger, and it certainly has a very high concentration of active ingredient. The pungent garlic aroma in these products dissipates to our nostrils after a few hours, but the sprays are said to deter all biting insects for two to six weeks, depending on rainfall and such.

Q. Are there any plants that can be put in containers on a deck or planted in the ground nearby to naturally repel mosquitoes? Did I read somewhere that marigolds could help? Thank you!
    ---Millicent in Federalsburg, on the Eastern Shore of MD
A. Let's discuss marigolds first, Millie, as you almost certainly have heard such a tale. Although these pretty posies have been reputed to repel pests ranging from mosquitoes to slugs, rabbits, and all the way up to deer, they do none of those things. As anyone who ever fell for those promises can assure you, rabbits, slugs, deer, groundhogs and virtually every other herbivorous garden pest greatly enjoy snacking on the tasty little posies. The only scientifically verified use for marigolds I've ever seen is their ability to deter root-knot nematodes, a serious pest of Southern crops. And even then, the grown flowers must be plowed into the soil to negate the nematodes.

And no plant sitting in a pot or in the ground will repel mosquitoes. But many plants DO have that ability when you crush up their leaves and rub the aromatic leaves on your skin. In University studies, lemon scented thyme was the clear winner; as effective as some formulations of DEET. And it's an ideal plant to grow in a container. Unfortunately, lemon thyme is also a very small plant with small leaves, and you'd need a lot of plants to insure a steady supply of summertime slap prevention. But it would be worth growing a lot of it; I grew lemon thyme again this year after a few years without having it around and am astonished by the citronella-like pungency of this attractive little herb.

But mostly I rely on the lemon balm in my garden. It's almost as effective as lemon thyme, rapidly achieves a large size, and is "easy to grow", which is hort-speak for a plant that falls somewhere between aggressive and invasive. Luckily, growing lemon balm in a container is a great way to help control it.

And last time I checked, catnip was still a big contender in the mosquito-repelling plant world, with research showing it can beat lemon thyme in some measures of potential effectiveness (and perhaps invasiveness).

Whatever pungent plant you choose, cut or pull off whole stems, turn the stems upside-down (for easier leaf removal), strip off all the leaves and rub the leaves on exposed areas of your skin. I also drop the cleaned branches on the ground around my feet for a little extra protection. No matter which plant you choose, try a small amount on a small area of your skin first to insure that you don't have an allergic reaction.

Oh, and if your plant containers have saucers or dishes underneath, ditch those dishes—all they're good for is holding water that drowns plants and breeds skeeters....

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