Fungus gnats live in soil. The gnats lay their eggs in the soil and their larva feed on the decomposing matter, they pupate and hatch into flying gnats which starts the cycle all over again. The best way to get rid of them is to break this cycle.
Put a thin layer (approximately 1/8th inch) of fine, clean sand on top of the soil in your containers; this keeps the adults from laying eggs and any pupae/larva from hatching. Trap any adults flying around with sticky traps or even a saucer of juice. That's it! Simple and it works. Stop the cycle and no more gnats!
Source: I work at a plant nursery and listen to gardening radio programs. A few years ago, on Garden Compass, this is what they suggested. I have been giving this tip to my customers ever since, and it has always worked, no complaints!
By LeeAnn from Redding, CA
This sounds great! What kind of sand do you use?
Doesn't the sand wash into the soil when you water?
I recently was given four large houseplants and now I have little black flies everywhere. I have also noticed little tiny bugs in the soil. How do I get rid of them? And I was also wondering if house plants carry bed bugs?
Diatomacious Earth. I always keep DE on hand for the animals and me too. The food grade can be used in the garden. On your indoor plants, sprinkle on top of soil. As it gets wet you will replace but the flies are hatching from the soil. Break the cycle. Easy. Natural.
Put playground sand on the top of the dirt. You can get it at walmart. Work's great. I think it keeps the flies from being able to hatch and get out of the sand.
I have little water flies. They like the damp ground in my indoor plants. How do I get them out of my house?
By Pat C.
Hairspray will kill them if you are dealing with just a few.
Mix a solution of 1 cup balsamic vinegar and 2 or 3 tbsp. of Dawn dish soap into a small cup or several small cups. The gnats will be attracted to it and climb in.
Or you could save jars and clean them out and pour vinegar into them and poke holes in the top of the jar.