How to Get Rid of Fungus Gnats in Your Houseplants (Once and For All!)

It’s never fun to bring home a new houseplant and THEN discover it has an infestation of fungus gnats!

It’s also NOT fun when those gnats seem to take over your house and other plants in what seems like a split-second.  But it can (and does) happen. Here are some of the best tips and tricks to get rid of those pesky gnats.

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What IS a Fungus Gnat?

Getting rid of a plant pest is easiest when you know a little background about the pest.

Fungus gnats are very common with houseplants, especially plants that are kept in humid locations and have continuously moist soil. The gnats are quite small at around 1/8-inch long – they sort of look like a fruit-fly. The larvae are worm-like in shape, are about 1/8-inch long, have a white almost transparent body and a black head. (Click images to enlarge)

There are two stages of a fungus gnat – the larva stage and the flying (adult) stage. The flying gnats don’t pose a problem for houseplants – they are just seriously annoying when they fly in your face! The adult gnats don’t bite, so they are harmless. It’s the fungus gnat larva that causes problems. The larvae live in the soil and feed on plant roots.

In order to get rid of fungus gnats, you need to get rid of the flying adults and the larvae. The adults only live about a week, but they can lay around 300 eggs! The larvae ‘hatch’ in about 5 days and start feeding on your plants roots. The larvae live in the soil (eating) for about 2 weeks before they emerge from the soil and start flying in your face. This cycle continues until you finally eradicate them, which typically requires repeated applications and techniques until all the eggs and adults are gone.

How to Tell If Your Houseplants Have Fungus Gnats

Trust me on this – you will definitely know when your plants have fungus gnats!

You’ll see the flying adults all around your plants, especially when you water the plants.

You might also see symptoms in your plant’s leaves as the larvae are damaging the plant’s roots – for example, wilting leaves, leaves turning yellow, or stunted growth.

How to Get Rid of Fungus Gnats

Getting rid of fungus gnats requires you to get rid of the flying adults and the buried eggs and larvae.

Because of the continuous growth cycle of fungus gnats, eradication is not usually a once-and-done thing. Several applications and techniques are typically necessary before you get rid of all the fungus gnats. The sooner you start this process, the sooner you’ll be able to eat your dinner without bugs flying in your face.

Here are some tried-and-tested methods of getting rid of this pest. I recommend you use each of these techniques.

Yellow Sticky Traps

Let’s start by trapping as many flying adults as you can.

• Place a yellow sticky trap into your potted plants. Gnats are attracted to the yellow color and will become stuck on the traps as they emerge from the soil. When the adults are trapped, they can’t lay eggs – so you’re removing one part of this vicious cycle.
• When the sticky trap is full, replace with another.  Depending on how many fungus gnats you have, a sticky trap can last a month or more.
• You don’t have to place a sticky trap in every single plant you have. One sticky trap will attract gnats from several nearby plants, so using one trap roughly every 6 plants or so will work.

Biological Control

The next step is to get rid of the eggs and larvae in the soil. While the eggs are laid in the first 1- to 2-inches of soil, the larvae burrow down deeper, so reaching all the soil is needed.

Mosquito Bits are not just for mosquitoes – these bits also kill fungus gnats larvae in the soil. Mosquito Bits are a biological control – Bacillus thuringiensis – that is non-toxic and is a naturally occuring bacteria. There are a couple of ways to use Mosquito Bits – either dissolved in water, or directly on top of the soil.

• Sprinkle Mosquito Bits on top of the soil of an infested plant. When you water the plant, the water will release the active ingredient in the bits into the soil, killing the eggs and larvae. Each time you water your plant, more of the Mosquito Bits will seep into the soil. Repeat this for at least three waterings, or until the fungus gnats are gone. Having Mosquito Bits on top the soil acts as a top-dressing that also helps deter adult fungus gnats from laying their eggs in the soil.
• Mix Mosquito Bits with water, then use the water to water your plants. Mix about 4 tablespoons of Mosquito Bits per 1 gallon of water. Allow the bits to soak for at least 30 minutes before using the water. Water plants as usual for at least three waterings. Repeat as necessary.

NOTE: Mosquito Bits are safe for people and wildlife. 

Alternatives / Additions:

• As an alternative (or addition) to Mosquito Bits is a product called AzaMax. The active ingredient in AzaMax (azadirachtin) helps to kill the fungus gnat larvae in the soil. Mix 1 tablespoon AzaMax per 1 gallon of water and water the infected plant every 5 days (or when you water the plant).
• Another alternative (or addition) to Mosquito Bits is using Beneficial Nematodes. Nematodes are very tiny, microscopic worms that kill fungus gnat larvae. Mix 1/4 teaspoon of nematodes per 1 gallon of water, then water plant as normal. Nematodes are safe for people, pets, and plants.
• As an alternative to using Mosquito Bits, systemic insecticide granules are also helpful in the control of fungus gnats. Add the granules into the soil and water them in. The pesticide will be absorbed into the roots of your plants, killing the larvae that feed on the roots.

Neem Oil

To completely get rid of fungus gnats, you will also need an insecticide to kill the pests on top the soil.  A product, such as Neem Oil, can be very helpful.

• Spray Neem Oil onto the surface of the soil, and on the plant or pot where there are fungus gnats. Neem Oil kills eggs, larvae, and flying fungus gnats (as well as other pests).
• Spray enough Neem Oil to really give the top layer of soil a good drenching.

NOTE: Neem Oil is safe for using around people and pets.

Additional Tips to Prevent Fungus Gnats

The techniques above will help you control fungus gnats that are already in your plants, but you can also prevent fungus gnats from entering your home in the first place.

• Inspect new plants before you bring them home – When you’re buying plants, make sure to look closely at the plant for signs of fungus gnats. You can also scratch into the soil a little bit to look for larvae. If you see gnats flying on the plant or soil, or larvae in the soil, it’s best to pass on that plant. TIP: A small, pocket-size magnifying glass can help you see the larvae in the soil.
  NOTE: If you decide to buy the plant anyway, keep it isolated from your other plants until you’ve treated it for fungus gnats. Once the gnats are gone, you can introduce the plant to your other houseplants.
• Inspect potting soil before you use it – Before using a bag of potting soil, check it (outside your house) for fungus gnats. These bags are not air-tight and the soil in the bags is often very moist – a perfect breeding ground for fungus gnats. If you find fungus gnats in the potting soil, treat the soil using the methods above, then store the eradicated soil in air-tight containers until you need it.
• Don’t overwater your plants – Overwatering plants provides the perfect environment for fungus gnats to survive (and it’s not good for your plants – see How to Water Houseplants for Best Indoor Plant Growth (and Success). Make sure to let the top 1- to 2-inches of soil dry out between waterings. Adult fungus gnats are not attracted to dry soil, and are much less likely to lay their eggs there. Dry soil also stops eggs from ‘hatching’ and larvae from growing.
• Bottom water your plants – If possible, water your plants from the bottom versus the top. Since fungus gnats lay their eggs in the first 1- to 2-inches of soil, bottom watering plants keeps the water at the bottom of the pot, keeping the top soil dryer, and less attractive to adult fungus gnats.
• Protect drain holes in pots – Sometimes fungus gnats find their way into pots through the drain hole of the pot. To prevent them from getting into the drain hole to lay their eggs, cover the drain hole with a piece of nylon stocking or similar fabric. This type of fabric will keep the gnats out, but also let the water drain from the pot.
• Add a top dressing to your potted plants – By adding a top dressing to the soil of your potted plants, it helps keep adult fungus gnats from laying their eggs in the soil. A product such as sand, gravel, or pumice can be helpful – a thickness of 1/4-inch is usually all you need to top dress the soil.

Follow all these tips and tricks, and you’ll be free of fungus gnats in no time!

Do you have any additional tips or tricks for getting rid of fungus gnats? Share in a comment below!