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How To Kill Gnats In The Soil - An Overview

How To Kill Gnats In The Soil – An Overview

Do you know how to kill gnats in the soil or do they keep annoying you repeatedly and destroying your houseplants?

Fungus gnats or soil gnats are some of the most common and annoying indoor pests.  These pests are attracted to high moisture and humidity.

You will start by noticing a harmless adult fly around your houseplants or gather around a closed window.  They are non-biting but they become a flying nuisance.

At the larvae stage, they feed on your soil damaging the tender roots of your plants. The worst thing about fungus gnats is that they infest any indoor plant growing in soils. This means, if you have indoor plants, they will get into every one of them.

In this article, we will learn how to get rid of these annoying pests for good!

How To Identify And Kill Gnats In The Soil

The adult fungus gnats are delicate, grayish-black, mosquito-like flies that measure about 1/8 inch long.  They have long legs and one pair of clear wings. They are not strong fliers and are noticeable around the potted plants, especially during watering.

Larvae or maggots have a shiny black head and an elongated whitish transparent body measuring about ¼ inch long.

Fungus gnats look the same as fruit flies, and most people seem to mistake these two.

How To Identify And Kill Gnats In The Soil

However, they are not the same type of bug. Fruit flies are interested in the fruit smell that fills the house and do not destroy the plants.

The Fungus gnats love to lay their eggs in damp soils where the larvae hatch and feed on fungus, small roots, and other organic matter in the soil.

Here’s an easy way to tell the difference.

  • Fungus gnats are tiny black bugs in the plant soil that fly around the plants.
  • Fruit flies are insects that fly around a fruit or the garbage disposal in your kitchen.

Do Gnats Kill Plants And Soil?

No, fungus gnats do not kill your houseplants. These pests are a nuisance because they fly around the house but rarely destroy your plants. Sometimes, if the infestation is heavy, they may cause root damage but in most cases, fungus gnats will only eat rotting roots.

Even though they are not a major problem for your plants, they are likely to drive you crazy.  Who wants all these flying insects all over their house?

Before we figure out how to eliminate them, it’s best to first understand where they come from in the first place.  Then we can make sure they never come back.

Do Gnats Kill Plants And Soil

Where Do Fungus Gnats Come From?

Fungus gnat infestation can come from anywhere.  The most common way that these insects can get into your house is if they are in the soil of your newly purchased plant.  Alternatively, they can also be in a bag of potting mix that you can bring indoors.

Fungus gnats can also be brought in with a plant that was outdoors during the summer. Worse still, they can fly in through the screen of an open door or window.

The Fungus Gnats Cycle

Fungus gnats adults have a lifecycle of about a week.  They lay up to 300 eggs in rich, moist soils and within 4 to 6 days, tiny larvae emerge.  They begin feeding on fungi, plant roots, or organic compost during their 2 week period.

Their pupae stage lasts 3 to 4 days before these young adults leave the soil and begin to fly around as adults.

The entire Fungus gnats life cycle from egg to adult may be completed in only 3 to 4 weeks depending on the indoor temperature. Because of their productivity and relative short gestation, the potted plants can host them at each stage — egg, larvae, pupae, adult —all in multiple generations at once.

Due to this, fungus gnat treatment requires repeated applications until there are no remaining eggs.

Kensizer 20-Pack Yellow Sticky Gnat Traps Killer for Indoor/Outdoor

Severe Infestation Damage

As much as we have said these gnats do not cause any harm to the plant, a severe infestation may cause some damage. The larvae are the most damaging to cuttings, seedlings, and young plants. Plant symptoms for heavy infestation include:

  • Sudden wilting
  • Yellowing
  • Loss of vigor
  • Poor growth
  • Loss or death of the plant

Plants that are lost to injury include:

  • African violets
  • Carnations
  • Geraniums
  • Poinsettias

How To Get Rid Of Fungus Gnats In The Soil

It is critical to undertake fungus gnat control as a measure to keep your house free of these annoying insects.

Here are ways to control Fungus Gnats

Inspect your plants thoroughly before purchasing for any signs of insect pests. Carefully turn up soil near the base of the plant looking for the glossy, clear larvae.  Do not buy any plant that has any signs of these gnats.

Fungus gnats thrive in damp soils; therefore, do not overwater your indoor plants, especially during cold months when plants use less water. When potting, avoid using water-holding containers, organic material like peat moss that may encourage egg-laying.

If you notice these pests are already present, leave your soil to dry to a depth of 1 to 2 inches between watering. This will kill the larvae and inhibit the development of eggs.  The dry soil also makes it less attractive to egg-laying females.

Use yellow sticky traps placed horizontally on the soil surface to capture large numbers of egg-laying adults. The gnats are attracted to colorful sticky traps so use yellow or pink ones.  Once stuck to the trap, you can easily remove them from the trap before they lay more eggs.

Use hydrogen peroxide as a soil drench by mixing 1-part peroxide with 4-parts water.  Pour it through the soil at the root zone until it comes out of the base of the pot. The peroxide kills these fungus gnat larvae on contact.

Use neem oil as an effective soil drench to combat fungus gnat larvae. Dilute the oil with water according to the manufacturer’s directions and drench the soil directly at the roots of the plant. You may also spray the upper part of the plant to keep adult gnats at bay.


It is easy to kill gnats in the soil using organic solutions that will not harm your plants or pets and is not toxic to your house environment. Go ahead, choose your favorite solutions, and eliminate these fungus gnats for good!