Small Flies in House Plants

When I first moved into my new home, I didn’t have anywhere to store my garden soil so I left a large bag of it our in the rain. I found out later that this water logged soil had picked up some pests from outside. But there were ways to handle the pests without harming the plants in the soil.

Before using these tactics, research the particular variety of plant that you have and make sure it can tolerate these practices.

This is a good alternative to throwing out an entire bag of soil.

The flies in potting soil are likely fungus gnats, which are small flies that are attracted to organic matter. 

How to get rid of fungus gnats

• Dry out the soil: Let the top 1–2 inches of soil dry out before watering again. 
• Use sticky traps: Hang yellow sticky traps near the soil to trap adult fungus gnats. 
• Use hydrogen peroxide: Mix one part hydrogen peroxide with four parts water and pour into the pot to kill larvae and eggs. 
• Use vinegar traps: Mix a few drops of dish soap with white vinegar and place near the plants. 
• Use beneficial insects: Use nematodes, predatory mites, or Bacillus thuringiensis to eat the larvae and pupae. 
• Use coarse grit: Layer the surface of the soil with coarse grit to create a barrier. 
• Use neem oil: Dilute neem oil with water and apply to the soil to kill larvae. 
• Use pyrethrin sprays: Spray the soil to kill larvae and adult gnats. 

How to prevent fungus gnats 

• Discard the top layer of soil and replace it with sand.
• Water from the bottom.
• Only water when the top couple of inches of soil is dry.