September 30, 2020

Are Your Plants Host to Uninvited Guests?

If you love houseplants, chances are you’ve had to deal with the annoyance of fungus gnats, also known as soil gnats. These small, dark-colored flying insects, which look similar to fruit flies, live in the soil of your indoor plants, with their larvae feeding on plant roots and fungi. The adult gnats make their irksome presence known when you water your plants or disturb the soil somehow.

Fungus gnats are attracted to the moist potting soil and decaying plant matter at the base of indoor plants. Their larvae may have been present when you acquired the plant at a store or nursery, so they weren’t visible until you got the plant home, at which time the larvae hatched into the adults. Infestation can also occur if your houseplant was outside for a period of time.

Fungus gnats don’t bite and usually don’t cause harm to mature, healthy plants. However, in young seedlings and fragile plants, they can cause yellowing, stunted growth or even death.

How to Get Rid of Gnats in Houseplants

Wondering how to get rid of gnats in the house, which buzz exasperatingly around you and your plants? Even though your first instinct might be to grab the bug spray, this is a limited solution because more gnats will simply hatch from the larvae in the soil.

More effective measures to rid your home and plants of fungus gnats involve targeting the larvae. Consider these simple ways to say goodbye to pesky gnats for good:

1. Don’t overwater your plants. Fungus gnats lay their eggs in the top inch of moist soil around the plant. Reducing excess moisture therefore hinders the eggs from developing into larvae. Allow the soil to dry out between watering — not to the point of the plant wilting, but leave enough time so that the soil is not continuously moist. The eggs and larvae usually die in dry soil, plus adult gnats are discouraged from laying new eggs. Furthermore, make sure your potted plants have adequate drainage.

To prevent future gnat infestations, water your plants from the bottom so that the top layer of soil stays relatively dry.

2. Soap and Water. Add a few drops of liquid dish soap or liquid castile soap, available at many major retailers, to a cup of water. Spray the top of the soil with this mixture to kill the gnat larvae. Repeat this in a few days to ensure you’ve completely destroyed all of them.
3. Layer with Sand or Gravel. Since fungus gnats’ eggs are in the top inch of soil, cover this with sand or gravel to create a dry environment. With the resultant lack of moisture and fungus on which to feed, adult gnats won’t lay their eggs there.
4. Soil Replacement. You might consider scooping the top inch of soil off your potted plant and disposing of it outdoors. Replace with fresh potting soil that has been in a sealed bag. Also, make it a habit to store unused potting soil in an airtight container, to keep gnats from getting into it and possibly laying eggs.

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