How to prevent gnats from taking over indoors

Credit: iStock / lightkeeper

Q: I had gnats and at the time I was caring for two very small children. I was unable to treat the gnats right away, and they spread, wiping out my entire (15-year-old) collection of houseplants. I gave up on plants for two years but brought them back into my house again to find the gnats are, once again, making a comeback.

I have been extremely over-cautious with watering, always watering in a sink, allowing water to drain completely, waiting for soil to be practically parched before I water again. I am sure there is an outside source infecting my plants.

I have heard to use sterile soil or some sort of man-made non-soil to prevent this? What are your thoughts on this?

Also, the article “Fungus Gnat Help” recommends applying a mite to a indoor houseplant? Sure, this may work to get rid of the gnats but what then of the mites living in your houseplants?

I will take any suggestions to rid myself of these annoying pests, aside from getting rid of my plants, again. I love having plants, and having them back in my house again reminded of how much I missed them.

Hopefully these few ideas will help you with your challenge:

1. Always use sterilized soil indoors, if possible mulch your existing soil with 1 inch of sterilized indoor soil.

2. Consider hypoaspis. Yes, you will have predatory mites on your house plants, but they are inconspicuous, beneficial and non-invasive. Check out the bug lady’s website at

3. Hang up yellow sticky cards to trap the flying gnats and cut off their life cycle.

4. Be sure not to over water, and always allow your soil to dry out before watering; fungus gnats love wet soil!

5. Haul your plants out doors this spring and rinse with Safers insecticidal soap and water.

6. Increase air circulation around plants, prune, open a window, be sure containers drain.

7. Fertlize your plants to keep them healthy and resist gnats; go for an organic 4*2*3. A product such as RainGrow would be helpful.

Best of luck! Today I am taking all my houseplants out to give them an annual wash and when I bring them in will feed and mulch. I find this really helps to keep them pest-free.