How To Get Rid Of Fungus Gnats


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Wondering how to get rid of fungus gnats? It’s not as hard as you think! Learn how to prevent and control gnats in your houseplants and seedlings naturally.

Having a home filled with houseplants can be a wonderful thing especially in the winter. It brings a warm and cozy feel to your home and a reminder that spring will come.

But keeping houseplants or starting seeds indoors can also bring unwanted pests into your home and cause damage to your plants.

One of the most common houseplant pests are fungus gnats and they can cause a lot of damage if left untreated.

The goodness is that they aren’t that hard to get rid of and prevent from coming back.

Close up of an adult fungus gnat. Text overlay reads How to get rid of fungus gnats.

What Are Fungus Gnats?

Fungus gnats are a small fly, about the size of a fruit fly, and a common pest for indoor houseplants.

The adult flies are tiny ranging in size from 1/16 to 1/8 of an inch (15 to 3mm) long while the fungus gnat larva can be up to 1/8 of an inch (3mm) long.

Adult fungus gnats are greyish to black in color and have either gray or transparent wings.

You might confuse them with mosquitoes because of their long legs and antennae. When they fly they are more erratic and slower than other flies this is another reason they can be confused with mosquitoes in your home.

The larva have a white or transparent body with a small black head and can be found on the soil surface or just underneath.

Lifecycle

Adult fungus gnat on a leaf.
Adult fungus gnat on a leaf.

Fungus gnats have 4 growth stages, egg, larva, pupa, and adult.

When a female gnat lays her eggs in the soil they take about 3 days to hatch in warm soil of 75F. After hatching the larva quickly grow through 4 instar stages before forming pupae 10 days later.

The pupae will emerge 4 days later as adults and the cycle starts again. The lifecycle averages 17 days but in warmer weather can be faster.

Adult gnats live for about 10 days and they can lay hundreds of eggs during that time.

Fungus Gnat Damage

Fungus gnats don’t bite and are more of an annoyance to people than harmful but they can cause a lot of damage to your houseplants or seedlings.

The larva feed on the fungus in the soil but as their populations get out of hand they can start feeding on plant roots. This of course can set back or kill your plants.

It’s especially bad for young plants and seedlings with a small root system. These gnats can also spread pathogens that cause damping-off disease another common problem with seedlings.

The damage can look similar to root rot and other soil problems. The plants lower leaves will start to turn yellow and fall off, and the plants growth may slow or stop.

In an extreme outbreak, the plant may even die if the roots are damaged badly enough.

When trying to find out if it’s a fungus gnat problem compared to root rot watch around your plant to see if you have tiny flies hovering around.

How To Get Rid Of Fungus Gnats

Yellow Sticky Traps

Yellow sticky trap covered in gnats.
Yellow sticky trap covered in gnats.

One of the easiest ways to control fungus gnats is yellow sticky traps. These small squares of yellow paper are covered in adhesive and can be placed on top of the soil or on small holders just above soil level.

Adult gnats are attracted to the color yellow and when they land on the traps they become trapped. While they work well for adults they won’t do anything to get rid of the larva.

Apple Cider Vinegar Traps

One of the simplest and cheapest solutions is to make a trap using apple cider vinegar. There are two easy versions of this trap you can make.

The simplest way is to take a shallow container and pour a little water, and apple cider vinegar inside. Then add a few drops of liquid dish soap and place the container near your potted plants, or on top of the soil if there is room.

My preferred way is to make a simple trap out of an empty pop bottle just like the one I use for getting rid of fruit flies.

Cut the top part off, then add half a cup of water and cider vinegar in the bottom, with a few drops of dish soap.

Then place the top part of the bottle upside down into the bottom part forming a funnel.

The smell of the cider vinegar attracts the gnats and they get trapped inside.

Neem Oil

Neem oil can also be used as a soil drench to help with soil fungus and to get rid of fungus gnat larva.

Remember to never use pure oils on your plants, dilute the oil using the manufacturer’s directions and water your soil with it. You can also spray the plant leaves to help deter adult gnats.

Hydrogen Peroxide

Hydrogen peroxide is my go-to way of controlling fungus gnat larva and other soil fungus problems in my houseplants.

Using a 3% mix one part hydrogen peroxide with four parts water and water your plants with it once a week until the gnats are gone.

Avoid getting this on the plant leaves as if the peroxide mix is to strong it can damage the leaves.

Flypaper

Yellow sticky fly ribbons can also be used to trap fungus gnats. Although they work well they are large and a bit more than you need to deal with the problem.

If you can find them using the smaller yellow sticky traps is a more practical option.

Soap And Water Spray

Both the adult fungus gnats and their larva are easily killed by good old soap and water.

Place a cup of water into a spray bottle and add a few drops of dish soap. Spray the top of your soil every few days with this mixture to kill the emerging larva.

If you see any adult flies buzzing around your plants you can also spray them with the soap mixture.

How To Prevent Fungus Gnats In Houseplants

Keep Soil Dry

Fungus gnats love moist soil, so letting your houseplants dry out a little between waterings can help to stop or slow down an infestation.

Just like when you have an outdoor garden, letting the top inch or two of soil dry out before you water the plant is best both for preventing root rot as well as gnats.

When adult gnats find your plants they may not want to lay their eggs in the dry soil as they know it’s not the best place for the larva to grow.

Water From The Bottom

Bottom watering is an easy way to water your houseplants and can help prevent you from overwatering.

Place your plants in a tray of water and let it sit just long enough to soak up enough water while keeping the top inch of the soil dry.

If you are trying to stop an outbreak of gnats but your plants need watering this can be a good middle ground.

Use Gravel Or Sand Mulch

Fungus gnats lay their eggs on the top of the soil. If you replace the top inch of soil in your house plants with sand or gravel it helps to create a dry environment without the natural fungus they feed on.

With a lack of food available the adult flies are less likely to lay their eggs in the soil around your house plants.

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