Madi from Oceanside, CA
Adults live about 7 to 10 days and deposit eggs on or in moist soil. The females lay from 100 to 300 eggs in batches of 2 to 30 each in soil containing decaying organic matter. The eggs hatch in 4 to 6 days and the larvae feed for 12 to 14 days. The pupal stage is about 5 to 6 days before adults emerge. Repeat.
The adult gnats are an annoyance, but they won't hurt your plants. The larvae, however, can damage the feeder roots and root hair causing a general loss of vigor to some plants.
The best way to prevent fungus gnats is to use a sterile potting soil mix when re-potting (one that is free of bark chips) and to make sure your pots have good drainage. These guys need a moist environment to feed and continue breeding. So if possible, it's a good idea to let the surface of the soil dry out as much as you can (without injuring the plants) between watering. This works well to kill the larvae.
Here are some other things to try:
Ellen
By tonya
By Joyce
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How do I get rid of little bugs that look like fruit flies in my houseplants?
Set out some apple cider vinegar in a bowl, with 1/2 teaspoon of vegetable oil, and a piece of apple or a banana peel and let it set out.
I have problems with gnats (I think that is what they are). I've noticed them throughout the house and they are coming from my plants.
How can I get rid of gnats! I have a lot of indoor plants and all of a sudden I am plagued by gnats. Have tried a mixture of cornmeal and water but can't get rid of them completely.