Question
Every plant in my house is now infested with tiny black flies or gnats.  How do I get rid of them without repotting all of my indoor plants (about 25).  They are flying all over the house and driving us crazy!!HELP!!!

Answer


Hi Cynthia,

Fungus gnat larvae live in decaying organic material (wet soil and rotting roots) where they feed. As adults they develop wings and fly out of the soil. The winged adults live for only about a week before laying eggs in damp soil and dying.

Start by assessing your plants and determining if there are any infested plants that you are willing to discard. For all of your remaining plants, scrape off and discard all loose soil from the surface that is not in immediate contact with roots. Gnat larva tend to live close to the soil surface so this will help eliminate many of the larvae. This will also allow the soil to dry out deeper into the pot.

Then, keep your plants as dry as possible. That means not watering them until they are close to wilting. For most plants the soil can dry about a quarter to a third of the way deep into the pot, but some can dry much deeper into the pot before wilting. This drying out will deprive the larvae of the necessary moisture they require. It will also help prevent decaying roots.

After about a week, you should start to see a noticeable decline in the flying gnat population as they die off and are not replaced with as many new gnats. It may take 4-6 weeks before you get rid of all or most of the gnats, so patience is required. Once the gnats are gone, continue to keep your plants as dry as possible otherwise the gnats may return.

I have written an article on plant pests that I will email for free to you (or anyone else) who sends a request to me at [email protected].

Please let me know if any of this is unclear or if you have any additional questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

Visit my website at  www.HorticulturalHelp.com