How to Get Rid of Gnats on Indoor Herbs

Those little gnats hovering around your indoor plants can be a real nuisance. But if you have an indoor herb garden, one you have spent time and effort nurturing, you don’t want these small pests to ruin the fruits of your labor. 

Some people are lucky enough never have to deal with gnats. But if you live in a warm area with a lot of moisture, gnat infestations are more common than you think. While they are less damaging to your herbs than other pests, like aphids, they can still cause problems. 

Aside from feasting on organic material like your herb plant roots – fungus gnat larvae can spread disease, causing stress to your house plants and inhibiting their growth.

The good news is that there are many all-natural ways to eliminate gnats on your indoor herbs. But first, let’s look at what fungus gnats actually are and how to tell if you have them.

What Are Fungus Gnats?

These little critters are easily identifiable due to their long legs, antennae, and transparent wings. Gnats are tiny and look like mosquitoes, but they don’t bite. Fungus gnats come in many different species – but it is the Sciaridae family of gnats that are a problem for indoor herb gardens.

Adult fungus gnats are attracted to the warm, humid environment that is an indoor herb garden. Gnats love moist soil and do not discriminate between healthy and unhealthy plants. It also doesn’t matter what your herbs are potted in, be it a large planter or a small pot, fungus gnats have no problem setting up camp!

What makes these pests different from others is the fact they do not usually attack the herb itself, but rather the roots. Fungus gnats will feed on plant roots, root hairs, and other plant material – destroying them in the process and leaving your herb unable to access much-needed nutrients.

Fungus gnats do not live long, but they can reproduce quickly by laying up to 300 eggs in their life. Gnats will lay their eggs in the wet soil, and before you know it, your herb garden will be dealing with a full-blown fungus gnat infestation!

What Causes a Fungus Gnat Infestation?

Fungus gnat infestations are typically caused by overwatering and/or poor drainage. The warm, wet conditions are ideal for fungus gnats to lay their eggs – providing a home for the harmful larvae to grow.

In addition, if you use potting mix that is not properly sterilized, it may contain fungus gnat eggs or larvae. When choosing a potting soil for your herbs, it is always best to go with one labeled ‘sterile’ or ‘pre-sterilized.’

Signs of a Fungus Gnat Infestation

While fungus gnats do not typically attack the herb leaves, it is fairly easy to tell if you have an infestation. The most common sign of a fungus gnat infestation is the presence of adult gnats flying around your herbs. Gnats are not great fliers, so they will stick close to the soil surface and dart around swiftly – usually in large numbers.

You may even see fungus gnat larvae in the soil. Gnat larvae looks like small, white worms and will remain near the soil surface. The larvae feed on the plant roots and organic matter, so it is essential to get rid of them as soon as possible.

Another sign of a fungus gnat infestation can be stunted growth or wilting in the plants. This is because the fungus gnats cause unseen damage within the soil and prevent your herbs from thriving. It can be hard to tell if this deterioration is down to gnats or another issue, but when paired with other signs of an infestation, it is a good indicator.

How to Get Rid of Gnats on Indoor Herbs

Now we know what fungus gnats are and how to tell if you have an infestation – let’s look at how to get rid of them. While there are many chemical solutions on the market, it is best to opt for natural solutions that are effective and safe to use on herbs.

1. Repot and Refresh

If you suspect your herbs may be hosting gnats, the first step is to repot your herbs. By removing the infested soil, you are cutting off the fungus gnats’ food supply and disposing of any larvae in the soil. If your herbs have any signs of root rot, they will need to be trimmed before repotting.

Before repotting your herbs in fresh, sterile soil, always thoroughly wash the plant pot to ensure no fungus gnat eggs are left in the container.

2. Cover The Soil

Fungus gnats thrive in moist soil and lay eggs in it. To prevent them from laying their eggs and interrupting the life cycle, add a layer of diatomaceous earth on the soil surface. Diatomaceous earth is a natural mineral powder that is safe for plants. It has a sharp texture that damages the fungus gnat’s exoskeleton, thus killing them on contact.

You must only use food-grade diatomaceous earth when covering the soil of herbs.

3. Try Mosquito Dunks

If you have never heard of mosquito dunks before, they are a type of biological insecticide that contains a strain of bacteria called bacillus thuringiensis (BTI). This bacteria is safe for humans and animals, but it is toxic to fungus gnats.

To use mosquito dunks for getting rid of fungus gnats, simply place one in a cup of water (or as directed) and add it to the soil. The bacteria will kill off any fungus gnat larvae in the soil, thus preventing them from maturing into adulthood.

4. Sprinkle With Cinnamon

I know this seems unlikely, but cinnamon is a great way to get rid of fungus gnats. Sprinkle a thin layer of ground cinnamon on top of the soil surface and use it in combination with other methods for maximum effect.

Cinnamon has anti-fungal properties, making it an excellent organic way to ward off fungus gnats. Plus, it smells lovely!

5. Create an Apple Cider Vinegar Trap

Many of the solutions in this list target larvae, which is vital in getting rid of fungus gnats. For a solution that targets the fungus gnat adults, try creating an part apple cider vinegar mix. The apple cider vinegar smells like sweet, ripe fruit to the gnats drawing them away from your herbs.

To make this mix, combine equal parts apple cider vinegar and water in a container (ideally a shallow dish or wide-rimmed bowl). Add a drop of standard dish soap and cover it with some plastic wrap. Then poke some small holes in the top and wait for the fungus gnats to be attracted to the mix! The soap will break down the surface tension of the liquid, making it difficult for them to escape.

6. Use a Hydrogen Peroxide Drench

You must use food-grade hydrogen peroxide for this remedy and correctly dilute the mixture. Hydrogen peroxide is safe for use on edible plants, as it breaks down into water and oxygen once it is released. This mix isn’t potent enough to harm your plants, but it does a great job of killing off fungus gnat larvae and eggs.

To create the drench, unless otherwise specified, mix one part hydrogen peroxide (3%) with four parts water in a watering can or spray bottle. Use this mixture to water the soil, not the leaves, being sure not to saturate the soil too much.

7. Utilize Yellow Sticky Traps

The bold yellow color of sticky traps attracts the fungus gnats, trapping them on the surface. Place a few of these traps around the herbs and monitor the results, replacing them when they’re full.

Yellow sticky cards are relatively inexpensive and are the best way to monitor the population of fungus gnats in your home. Although it is important to note these traps only catch adult gnats, so you’ll still need to use other methods for the larvae and eggs.

How to Avoid Problems With Fungus Gnats

Ideally, we want to do our best to prevent fungus gnats from invading our herbs in the first place. Here are some tips to keep in mind:

• Make sure the soil is not overly moist – gnats hate dry soil.
• Ensure good drainage holes are present in the bottom of the pot.
• Inspect new plants and consider ‘quarantining’ them.
• Thoroughly check new bags of soil for signs of gnats prior to using.
• Water your herbs from the bottom by placing them in a shallow bowl instead of pouring water directly onto the soil surface.
• Keep your herb garden clean and free of decaying plant matter.
• Stay on top of maintenance by regularly inspecting your herbs and checking for signs of infestation.

Preventing fungus gnats is key to keeping your herbs healthy and thriving. But if an infestation occurs, the above solutions should help you get things back to normal. Remember, the key to success when trying to get rid of fungus gnats is persistence and patience – you’ll soon be back to having beautiful and healthy herbs in no time!