How to Get Rid of Fungus Gnats in Houseplants Naturally

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If you have a collection of houseplants, you've probably had to deal with fungus gnats at some point. If you're a new plant parent, you'll likely face this problem sooner or later. Although a few gnats may not seem like a big deal at first, these pests multiply rapidly and can infest your growing space in no time. Fortunately, it's not too difficult to get rid of fungus gnats if you only have a few. Infestations can take longer to remedy but there are effective ways to get rid of these pests without spending a lot of money or having to call in a professional.

Although it may be tempting to break out the chemical sprays, please don't! Synthetic chemicals are no more effective than the natural remedies discussed here (sometimes they are not effective at all) and they will cause your indoor air to be polluted. This is especially dangerous if you have asthma or other respiratory ailments, or if you have young children or pets at home. Read on to find out how to identify fungus gnats, understand the conditions that attract them to your plants, get rid of them, and prevent them from returning.

How do you Know They're Fungus Gnats?

Before breaking out the remedies, it's important to find out if that's really the problem you're dealing with. So how do you know that the gnats you see buzzing around your plants are fungus gnats and not some other type of gnat or flying insect?

Fungus gnats are small flies that look like tiny mosquitoes, with adults about 1/16 to 1/8 inch long at full size. Part of the species Orfelia and Bradysia, fungus gnats are distinguished by their narrow legs, light gray or clear wings, and segmented antennae that are larger than their heads. They are often mistaken for fruit flies, which have different bodies, feeding, and breeding habits. While fruit flies are attracted to decaying fruit, fungus gnats are attracted to the warm and moist environment that indoor potted plants create.

Python (Peter Rühr), CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons

Although they may seem harmless at first, fungus gnats can cause a lot of damage to your houseplants.

Adult gnats are not the real culprits: while adults don't pose a major threat to plants, their larvae do. The larvae of fungus gnats eat the tiny feeder roots of plants, which can lead to significant root damage. Consequently, your houseplant's damaged roots can't take up nutrients effectively, which ultimately stunts its growth. If your plants seem to be wilting (despite being watered adequately) and lack vitality, and you have seen gnats flying around them, there's a good chance that fungus gnat larvae have damaged the roots of your plants.

The Fungus Gnat's Life Cycle

It's helpful to understand the life cycle of a fungus gnat so you can get rid of them more easily. These pests have four stages in their life cycle: egg, larva, pupa, and adult.

• Stage 1: Female fungus gnats lay their eggs in damp soil or potting mix. They can lay up to 200 eggs at a time. The eggs are tiny and difficult to see with the naked eye.

• Stage 2: In this stage, the eggs hatch into larvae, which are small, worm-like creatures that live in the soil. They feed on organic matter and plant roots.

• Stage 3: After feeding for about two weeks, the larvae pupate and enter a resting stage. During this time, they transform into adult gnats.

• Stage 4: As adults, fungus gnats seek to breed and start the cycle all over again. They are attracted to light and moisture, and they will continue to lay eggs in damp soil, perpetuating the infestation.

Now that you understand the life cycle of fungus gnats, it's important to understand what causes them to infest your plants.

What Causes Infestations?

Fungus gnat infestations in houseplants can be caused by a variety of factors. Understanding these causes can help you prevent future infestations and effectively get rid of existing ones. Here are some common causes of gnat infestations:

• Overwatering: Fungus gnats thrive in damp conditions, so overwatering your plants creates an ideal environment for them to breed and thrive. Don't water all of your plants on a schedule at the same time; instead, make sure to only water your plants when the top inch of soil is dry.

• Poor drainage: If your plants don't have proper drainage, excess water can accumulate in the soil, creating a perfect breeding ground for fungus gnats. Ensure that your pots have drainage holes and use well-draining soil. Adding perlite to your soil can help with drainage.

• Organic matter in soil: Fungus gnats feed on organic matter, so if your potting soil contains a lot of decomposing material, it can attract these pests. Choose sterilized potting soil or amend with perlite or vermiculite to improve drainage and reduce the amount of organic matter.

• Infected plants: If you bring in new plants without inspecting them thoroughly, you could unknowingly introduce fungus gnats to your existing plants. Always inspect new plants for any signs of infestation before introducing them to your indoor garden. If they do have pests, be sure to isolate and treat them before placing them near your other plants.

What works and doesn't work

While getting rid of fungus gnats isn't hard, you should be wary of some of the advice out there. There are remedies that work well, remedies that may work well in some cases and not so well in others, and remedies that flat out just don't work.

There are a number of remedies that work to varying degrees. Allowing your soil to dry out helps in most cases, but won't get rid of fungus gnats right away, using yellow sticky traps works well but takes time, and spraying neem oil or insecticidal soap mixed with water is a great control, but it will only kill the adults, which have to come into direct contact with it. Adding beneficial nematodes (microscopic worms) to the soil can help control fungus gnat larvae. However, nematodes can be expensive to purchase, may not be available in your area, and can only be stored in your refrigerator for so long before they die.

There are several other remedies that just don't work when it comes to getting rid of fungus gnats in houseplants. These include withholding water for long periods of time, which can stress your plants and make them more susceptible to insect infestations and diseases. Chemical pesticides can harm your plant and may not effectively target the gnats themselves. Cinnamon, which is a widely touted remedy, has some antimicrobial properties, but is not a reliable solution for getting rid of fungus gnats. Finally, apple cider vinegar or red wine traps or potato slices attract and catch adult fungus gnats, but do nothing to address the root cause of the problem.

Natural Ways to Eliminate Fungus Gnats

Allow the Soil to Dry Out

One natural remedy to get rid of fungus gnats is to allow the soil in your houseplants to dry out. Fungus gnats thrive in damp conditions, so by allowing the top inch of soil to dry before watering again, you create an environment that is less favorable for their breeding and survival. Check the moisture level of the soil before watering. Use your finger to determine when the top inch of soil feels dry to the touch. If you are unsure of your ability to do this, use a moisture meter. They're cheap, effective, and widely available.

Use Neem Oil

Neem oil is a natural insecticide that can be effective in controlling fungus gnats. Mix neem oil with water according to the instructions on the bottle and spray it onto the soil of your houseplants. The oil will suffocate the larvae and disrupt their life cycle, reducing the population of fungus gnats over time. Be sure to thoroughly coat the soil and repeat the application every 7-10 days until the infestation is under control.

Remove decaying matter

Eliminate any decaying matter in and around your houseplants. Look for dead leaves, fallen debris, dead insects, or mold growth. Remove any of these items from the soil and dispose of them properly. As mentioned earlier, fungus gnats are attracted to organic matter, so removing any decomposing material will deter them from infesting your plants. You can also prevent the accumulation of decaying matter by avoiding overwatering your plants.

Spray Soil

Mix equal parts of 70% isopropyl alcohol and water in a spray bottle. Spray this solution onto the soil, again making sure to cover the entire surface. The alcohol will kill the adult gnats and their larvae. Repeat this process every few days until the infestation is gone.

How to treat a major infestation

If your fungus gnat problem has reached the stage of a major infestation, the remedies above may not solve the problem effectively, since adults reproduce so quickly and all of them may not be killed right away with sprays or traps. When you're dealing with a major infestation of fungus gnats, it's important to take more aggressive measures. You may need to try several of the remedies below, along with the few already mentioned, at once.

Move the plant

If you've tried various natural remedies to get rid of fungus gnats and haven't seen significant improvement, it may be helpful to move the affected houseplant to a different location. Fungus gnats are attracted to moist environments, so moving the plant to an area with better air circulation and lower humidity levels can discourage their presence.Find a spot in your home where there is good airflow and sunlight, such as near an open window or under a fan. This will help to dry out the soil and create a less favorable environment for fungus gnats.

Change the Soil

If the infestation is severe and persistent, it may be necessary to completely change the soil in your houseplant. Remove the plant from its pot and gently shake off any excess soil. Dispose of the old soil in a sealed bag to prevent any remaining gnats or larvae from spreading. Rinse the roots of the plant under running water to remove any remaining pests. Then, repot the plant in fresh, sterile soil. This will help eliminate any remaining eggs or larvae in the old soil and create a clean environment for your plant.

Use Mosquito Bits

Mosquito bits are a natural and effective way to get rid of fungus gnats. Mosquito bits contain a bacteria called Bacillus thuringiensis(BT), which specifically targets the larvae of fungus gnats and mosquitoes. Sprinkle the mosquito bits onto the soil of your houseplants, following the instructions on the packaging. The BTI will kill the larvae upon contact, reducing the population of fungus gnats over time. Alternatively, you can make a 'tea' using mosquito bits and water the plants with it. Repeat the application every 30 days to prevent future infestations.

Kill Larvae with Hydrogen Peroxide

For hydrogen peroxide to work effectively, mix one part of the peroxide with four parts of water. Use this solution to water your plants. It'seffective against fungus gnats while being gentle on your plants. To achieve optimal results, reapply the hydrogen peroxide and water mixture weekly until you see that the gnats have been completely eliminated. A weekly application will disrupt their life cycle and prevent potential re-infestation.

Consider creating a soil barrier

If you're dealing with a persistent fungus gnat infestation, creating a soil barrier can help prevent them from laying eggs and reproducing. You can create a barrier by sprinkling food-grade diatomaceous earth or sand on top of the soil. These substances are abrasive and will deter fungus gnats from landing on the soil to lay their eggs. Additionally, they can suffocate any larvae already present in the soil. Make sure to reapply the barrier after watering or if it gets disturbed.

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Prevention is the key!

The best way to deal with fungus gnats is to prevent them from infesting your houseplants in the first place. Proper plant care is key here: you'll have to make sure you adopt healthy plant care practices, including an appropriate watering schedule and amount, according to each plant's needs, and avoiding heavy or compacted soil mixes that retain moisture for extended periods. Following some of the suggesting above, especially when bringing a new plant into your home, will go a long way in helping you avoid attracting fungus gnats in the first place!

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