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indoor plants #817068

Asked November 30, 2022, 10:22 AM EST

how can I get rid of flies from indoor plants. The flies look like fruit flies, but they are not. They are small and slightly lighter in color. How can I prevent this and what should I do to infecting other plants.

Hennepin County Minnesota

Expert Response

These are fungus gnats. They thrive in soils that are constantly wet due to overwatering and / or poorly drained planters. The larvae feed on fungus that grows in the soil and on roots in these wet conditions. The larvae pupate and emerge as the flying adults. Sometimes these insects come indoors with plants that have been outside all summer. 


Managing insects on indoor plants has several recommendations for dealing with these pests. For fastest relief, my recommendation is to repot your plants with new potting soil and new pots or pots washed in hot, soapy water. When you remove the plants from their containers, wash off the roots to remove any larvae / pupae. Check your plant's roots. They should be creamy white and firm. If roots are brown and mushy (root rot), prune these off. If a majority of the roots on a plant are rotted, you should dispose of the plant. It will not have enough root mass to grow well and will eventually die. Roots need both air and water to grow well. This is why drainage is so important to plant health.

Overwatering is the number one way we kill houseplants. TLC (tender loving care) becomes TMC (too much care). So avoid watering plants on a schedule like every Saturday morning. Water your plants only when they are dry and allow plants to dry out between waterings. Make sure your planters drain well and plants are not left sitting in water. To water, set the potted plant in the sink, water and allow excess water to drain completely. Then return your potted plant to its original location. 

After repotting, place yellow sticky traps (available online and in garden centers) in your plants to trap any remaining fungus gnats. They are attracted to the yellow color. Replace the traps if they become covered ion fungus gnats. You can stop using them when you see no more insects on them.
Julie Weisenhorn Replied November 30, 2022, 10:41 AM EST

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