Friday, January 8, 2010

Getting rid of gnats in houseplants

Remember a few months ago I was having a problem with all kinds of critters like whiteflies in the warm weather? I thought I would have a reprieve in the winter, but it seems that I'm being overrun with gnats now.

Gnats (or going by their official name, "fungus gnats") are the same general size as fruit flies (which are tan) or whiteflies (which are, of course, white), but are black. They don't bite or even hurt the plant (except for really young plants and roots) or anything like that, but they're super-annoying because like mosquitoes, they like to buzz in your face and your houseguests' faces at the most inopportune times.

For the past week, I've been obsessing with getting rid of these critters, so I've searched high and low on the Internet for answers. I suppose solace is to be taken in the fact that if these things are bothering you, you're certainly not alone.

Here are some tips for getting rid of them.
  • First and foremost, get them at the source. Gnats love to lay eggs in houseplants, especially houseplants that are overwatered and have decaying matter in the pots. Here are some basic things you can do short of throwing your houseplants out:

    • Let your plants dry out completely between waterings. This will kill any eggs and larvae that managed to slip in. Your plant will wilt, but it'll survive, but the fly eggs and larvae won't.

    • Clear out any dead foliage in your plants. Gnats love decaying plant material.

    • Repot your plants with clean soil.

    • Consider piling a bunch of sand on top of your soil.

    • Consider using saran wrap or aluminum foil to cover up the top of your flower pot so the soil is not exposed and flies can't get in.

  • Use cinnamon. That's right, cinnamon. Buy a huge jar at BJs or Costco, and dust a whole lot of the powder onto your houseplants' surface. Any flies on there will scram, because they hate the smell. And they'll never lay their eggs there.

  • Get a handheld vacuum cleaner (I like the Dyson Handheld Vacuum). When you see one, suck it up. Not only do you get rid of one more gnat, you get the enjoy the satisfaction of seeing them buzz around in the canister instead of in your face like some kind of odd science fair experiment.

  • Make your own trap. Just get a jar with a tight lid. Fill it with a substance that gnats can't resist, cover the lid, and poke holes in it. The gnats will fly into the jar but they won't be able to fly out, so in a bit of poetic justice, they'll end up drowning in the very concoction they so greedily tried to get. There are a million suggestions of what to add into the jar, I've heard people say the rind of a lemon, white wine, apple cider vinegar, an old piece of a banana peel or lemon.

  • Invest in some Yellow Sticky Traps from Gardener's Supply Company. These worked like a charm with whiteflies before, and they seem to be working like a charm with the gnats. The critters are attracted to the bright, very sticky yellow paper and will fly right into them to their demise. As a bonus, they'll act as a "fly detector" too...put them around your Aerogarden and around your houseplants, and the one with the most flies stuck to it will provide a hint as to where the bugs are laying their eggs.

  • Make sure there's no standing water or rotting food in the house.  If there are, gnats will find them before you do.

  • If nothing else, you have a chance to practice your "Mr. Miagi". You don't have to use chopsticks, but it's definitely in your best interest to use your kung-fu skills to smack them with your hands as soon as you see them. An adult can lay 150-300 eggs at a time, so you need to eradicate them as soon as you see one. They are rather quick--there was one the other day that I couldn't get no matter how quickly I clapped my hands, so it ended up sounding like I was giving it a round of applause.

  • Some people swear by hydrogen peroxide. You basically mix 1 parts H2O2 to 4 parts water, and then water your plants like normal. The mixture will supposedly destroy the gnat larvae in your plants as O2 is released (think of how peroxide reacts when you put it on a cut), but then after the reaction turn to good old fashioned H2O. For me, this didn't quite work, but if you happen to have peroxide around the house it's worth a shot.
  • Now, where your Aerogarden is concerned, gnats love moisture, and they WILL find the hole in your seed pod. And there is nothing quite as revolting as seeing a bunch of little white larvae in your seed pods. Once your plant is mature, consider taking a little aluminum foil and covering up the hole, and constantly checking the leaves and the waters for critters.   
I'm not sure how all these gnats got into my house, but I'm trying all of the above to get rid of them. What seems to be working the best are the yellow traps, which I've taped to the sides of my Aerogarden. The next best thing, believe it or not, is the white wine. Each morning I see a few more flies in the jar who partied just a little too hard the previous night.

UPDATE: Since I wrote this a few years ago, I've had to deal with a couple more infestations. Here are two other tactics that work well, if none of the above work for you.
  • Beneficial nematodes. These are microscopic parasitic worm-like organisms. Now before you start freaking out, I should say that these are good parasites. They're harmless to humans, pets, and plants, but deadly to fungus gnats. Specifically, once you release these little guys into your houseplant's soil, they'll home in on the fungus gnat larvae and (get ready to get disgusted), bore into their bodies and release a bacteria that kills the larvae within 48 hours. Then, like Luke Skywalker living in his Tauntaun, it'll use the shell of the body, feeding off of it and the bacteria. Long story short, after a while all your fungus gnat larvae is quite literally dead meat.

    Nematodes are easy to use; I've bought them from Gardener's Supply Company and from Amazon and have had good success with both in the past. In both cases, you're sent actual live nematodes in the mail (usually packed with an ice pack to keep them live during shipment). They'll be embedded in a spongy material (in the case of Gardener's Supply) or look like a white powder (from Amazon), which you mix into a gallon of water. If you look really, really carefully, you'll notice tiny little squirming things, who will be your new best friends. You water them into your plants and let them do their thing. 
  • Nematodes worked for me wonderfully the first time I tried them, but for some reason the second time I tried them they failed--the number of gnats got less but there were enough survivors to spawn a new generation--and because nematodes are pricey I couldn't afford to spend more money. That's when I turned to Gnatrol. Unlike nematodes, Gnatrol is not a living organism, but rather a bacteria found naturally in soil. Instead of being eaten, gnat larvae eat this bacteria (Bacillus thuringiensis subspecies israelensis) and then the bacteria produces proteins that react with the larvae's gut lining, basically making them unable to eat. Sure, it sounds a little mean, but after weeks or months of breathing in random gnats, you'll be thankful for it. 
Hopefully one of these tips can help you finally get rid of fungus gnats. 

1 comment:

Gardener's Supply said...

Thanks for suggesting our sticky traps for the fungus gnats. Another good option for houseplants are beneficial nematodes. The come in a product called Gnat Guard.,34-299,default,cp.html

Good luck in the battle. -David, Gardener's Supply