How to Prevent and Get Rid of Fungus Gnats on Seedlings

Fungus gnats can multiply by the hundreds quickly, infesting your home quickly despite their short lifespans. The rest of this article will explain what you should do if you find yourself having a fungus gnat problem, or you simply want to prevent one. 

Fungus Gnat

Fungus gnats can be prevented by watching how much you are watering your plants and minimizing the amount of decaying organic matter in your home. If you find yourself with a fungus gnat problem, they can be killed with sticky traps, flying insect spray, and apple cider vinegar. 

What are Fungus Gnats?

Fungus gnats are never a welcomed sign in any home. Small, dark insects that live in soil or fungus around the home, fungus gnats closely resemble fruit flies. 

Adult fungus gnats can be characterized by having long, slender bodies that slightly resemble mosquitos. Most of these small flies have grey-colored wings with a Y-shaped vein on them. Generally, these flies measure about 1/8th an inch. 

Fungus gnat larvae are usually white in color and have small black heads, and live in the soil of plants feeding on organic materials such as plant roots, root hairs, and fungi. 

How do Fungus Gnats Enter the Home?

Fungus gnats find their way inside your home through open doors or windows, and oftentimes find moist or decaying matter to live in and breed. This can be drains, trashcans, or other places that may contain decomposing organic matter. 

More often than not, you will be the one to bring fungus gnats inside your home. Chances are, you won’t know it until it’s too late. These small insects hide in the soil of your plants! 

Many find that their fungus gnat infestations become worse during the fall and winter, as those are the months that outdoor houseplants are brought inside to stay warm. 

Why are Fungus Gnats Bad?

Adult fungus gnats are no danger to humans or plants, as they do not feed. That being said, despite their short lives, fungus gnats can lay anywhere from 100 to 300 eggs per adult. Although adult fungus gnats are not much more than an extreme annoyance when out of control, the larvae can do a lot of damage to young plants. 

Fungus gnat larvae feed on organic material located in the soil of plants and will feast on the roots of many indoor plants. This can lead to big problems for young houseplants and can be fatal to young seedlings. 

Thankfully, there are ways to kill fungus gnats and prevent infestations in the future. 

What Will Damage To Your Plants Look Like?

Fungus gnats do the most damage to young houseplants and seedlings. They can cause wilting, yellow leaves in young plants by the larvae eating the roots. Seedlings can suffer from stunted growth or even death from this, as their root systems aren’t even fully developed. 

Fungus Gnat Leaf Damage

How to Prevent Fungus Gnats on Seedlings

Although adult fungus gnats are relatively harmless to houseplants, the larvae they breed can do quite a bit of damage to young houseplants and seedlings. Considering one adult female fungus gnat can lay up to 300 eggs during its one week of life, this can quickly become a very big issue. So how can it be prevented?

Fungus gnats are known to lay eggs in damp soil. They love decaying organic matter, and are very often found in greenhouses! Here are a couple of ways you can prevent a fungus gnat infestation in your home. 

Watch How Much Water You Give Your Plants

Because fungus gnats love moisture and will lay their eggs in the damp soil of your house plants, you should make sure that you are not overwatering your plants. To make sure that these pests don’t have the opportunity to become a bigger problem, you should try to make the environment they thrive in inhospitable.

Adult fungus gnats and their larvae are unable to survive in dry soil. By allowing the soil to dry out, you will prevent fungus gnats from laying their eggs in the soil and hatching.

If you must, you can add perlite to the potting mix. This will improve the drainage, and help prevent fungus gnats.

If you tend to overwater your plants, you should also check to make sure that any extra water in the saucers under the plant is emptied.

Water from the Bottom

Fungus gnats lay eggs in the top layer of soil your plants live in. If you water your plants from the bottom, it will allow the topsoil to stay dry and inhospitable. This will keep your plants happy and hydrated while also preventing fungus gnats.

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Minimize Debris Around the Home

Fungus gnats love decaying organic matter, especially plant debris. They will take over whatever they can find, laying their eggs there. To prevent this, make sure that any decaying organic matter, such as fallen leaves, fruit, or flowers, are cleaned up. Check your plants often and remove these items whenever necessary.

Additionally, you can look into using potting mixes that are free of composted ingredients. This can be bark fines, actual compost, or processed forest products. This can minimize the chance of a fungus gnat infestation happening.

Secure Extra Potting Soil in Safe Container

It’s really easy to use some potting soil for your plants before simply tossing the rest of the bag to the side. This makes it easy for fungus gnats to enter the bag of potting soil to lay their eggs, and before you know it, all your plants are infested, and your seedlings are dying.

To prevent this, you should store your extra potting soil in an airtight container where fungus gnat eggs and larvae are unable to survive.

How to Get Rid of Fungus Gnats on Seedlings 

If you find that the infestation has already begun, there are some extra steps that you can take to get rid of the fungus gnats. 

Use Sticky Traps

Although this step won’t get rid of the already existing larvae, it’s necessary to stop adult fungus gnats from laying even more eggs. Since female fungus gnats can lay up to 300 eggs, it’s so important that you first take steps to get rid of the source of the problem.

Sticky traps will catch adult fungus gnats flying around your home and can even be placed on little wooden stakes inserted in their soil. This will catch a ton of fungus gnats, as they love to crawl and fly around your plants.

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Flying Insect Spray

If you find that you can’t wait for traps to capture and kill the fungus gnats that have invaded your home, you can try to kill them with a flying insect spray. These are generally made with essential oils and will kill the flies quickly while being safe to use around your family and pets.

Use A Mixture of Soap and Water

You may have heard of people using apple cider vinegar to capture these pests. Although vinegar works great for fruit flies, many have found that a simple mix of soap and water is more effective to capture fungus gnats.

All you need is a cup, some water, and a couple of drops of liquid dish soap. Add this to a spray bottle and spray the topsoil of your plants with it. It will kill the larvae living there. If needed, repeat every few days.

Dispose of Topsoil Outside

Eggs already laid in the topsoil of your plants may still hatch no matter what. If you can, take out the infested layer of topsoil, dumping it outside your home. The eggs will still hatch, but at least it won’t be inside!

Sand and Gravel

As stated previously, fungus gnats tend to only lay their eggs in the very top inch of soil your plants are planted in. If you can replace the topsoil with a layer of sand or gravel, the fungus gnats will not be able to survive off the nutrient-rich fungus located in that moist soil.

Instead, they will be faced with a dry, inhabitable environment without food sources.

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Control Larva

There are a couple of different ways to control larvae if they have infested your houseplants. The first and most popular way is by using a slice of potato!

Take the potato and add it to the surface of your soil. The larvae will be attracted. By it and start feeding on it. You can use this slice to dispose of the larvae you can collect.

Final Thoughts

Fungus gnats are never a welcomed sight in any home, and they can be extremely hard to get rid of if you don’t know what they are, where they came from, or where they are breeding. 

By figuring out what the pest is and how to stop the breeding, you will be able to stop the infestation, and hopefully prevent it from happening again in the future. 

It’s important to give your seedlings a chance to grow and thrive, and allowing fungus gnat larvae to find their way into your houseplants will prevent that from ever happening.