Fungus gnats, also called soil gnats, are tiny bugs that crawl in the soil and fly around your indoor plants – and they are extremely annoying.
The worst part is that they can infest any plant that’s potted in soil. Which means they can get into every single one of your indoor plants.
But the good news is that you can eliminate them and prevent them from ever coming back. In this detailed guide, I’m going to show you exactly how to get rid of fungus gnats – FOR GOOD!
What Are Fungus Gnats?
Fungus gnats are tiny black bugs that crawl on top of the soil and fly around your houseplants. They are the most common houseplant pest there is, and they can quickly infest your entire collection. Yuck!
The adult females lay their eggs in the soil, and the larvae (tiny white worms that are barely visible to the naked eye) feed on rotting roots and other organic matter. Thankfully they do not infest the leaves or stems.
Though the look very similar to fruit flies, they are not the same type of bug. You can read all about how to tell the difference between the two here, so you can make a positive ID.
Related Post: How To Make A Homemade DIY Fruit Fly Trap
Fungus Gnat Life Cycle
There are 4 stages to the fungus gnat life cycle: egg, larvae, pupa, and adult. In the right environment, they can multiply very quickly, and their full lifespan can happen in less than a month.
It takes about 5-6 days for the eggs to hatch, and then the larvae will feed for 10-14 days before they pupate. The full-grown adults will emerge from the pupa in another 4-6 days.
The adults only live for a week or so, but the females can lay hundreds of eggs during their life. So if you don’t take the right steps to eliminate them, their population can explode in a short amount of time.
Will Fungus Gnats Kill Plants?
The short answer is no, fungus gnats will not kill your houseplants. They are usually just a nuisance and rarely destructive.
Sometimes they can cause minor root damage if the infestation is heavy, but normally they only eat rotting plant material.
Even though they aren’t a huge problem for your plants, they are likely to drive you crazy, right? I mean, who want fungus gnats flying all over their house? Not me!
Related Post: How To Get Rid Of Houseplant Bugs Naturally
Where Do Fungus Gnats Come From?
Though indoor plant bugs can come from anywhere, here are the 4 most common ways that fungus gnats could have gotten into your house:
- In the soil of a new plant
- An infested bag of potting mix
- Plants that were outside during the summer
- Through the screen of open windows or doors
How To Get Rid Of Fungus Gnats In Plants
The key to getting rid of fungus gnats is to eliminate the larvae. Since the adults only live for a few days, once all the larvae is dead, the infestation will go away pretty quickly.
This is easier said than done though. The adults can fly, jump, or crawl from one plant to the next, so it can be difficult to eradicate them.
So you have to be persistent in treating them, and ensure that you are diligent about keeping your houseplants healthy to prevent recurring outbreaks.
9 Effective Fungus Gnat Treatment Methods
There’s no need to resort to chemical pesticides, you can easily fight these pests using natural and organic treatment methods. For the quickest results, you should try all of these:
1. Proper Watering
The #1 reason fungus gnats get into your plants is from overwatering. The larvae thrive in wet soil, and they can’t survive when it’s dry.
So, the easiest and most effective method of eliminating them is to make sure you always water your houseplants correctly. The soil should feel dry to the touch, and never be saturated or soggy.
If you struggle with this, I highly recommend getting an inexpensive moisture gauge to make sure you get it right every time.
2. Water From The Bottom
Fungus gnat larvae live in the top 1 inch of the soil, which tends to stay pretty moist when you water plants from the top. So if you have persistent problems, then try watering from the bottom instead.
To do that, simply pour water into the drip tray or cache pot, and allow the plant to soak it up through the drainage holes in the bottom of the container.
Always dump out any remaining water after about 20-30 minutes, and never leave your plant soaking for longer than that.
3. Use Traps
Putting a yellow sticky trap near your indoor plants is a super safe pest control method that will attract and capture the flying adults.
This only works to control the adult population, it will not take care of the problem at the source – the larvae.
But these traps will definitely prevent fungus gnats from flying around to other plants, and help you get them under control faster.
4. Apply Organic Products
There are several organic products that you can pour over the top of the soil to help kill the gnat eggs, larvae, and pupa.
It might take a few applications to see results, and you also have to be careful not to overwater your plants in the process. Here are a few of my favorites:
- Insecticidal soap – This will kill any bugs in the soil on contact. You could also make your own by mixing 1 teaspoon mild liquid soap with 1 liter of water.
- Neem oil – This is a natural pesticide that works to kill houseplant pests over time, and it has a residual effect to help keep them away.
- Beneficial nematodes – These are microscopic organisms that will feed on the pupa and larvae, and you can simply add them to your watering can.
- Bacillus thuringiensis israelensis (BTI) – Is a bacteria that’s only toxic to the larvae of bugs like fungus gnats, but it takes some time for it to be effective.
Related Post: How To Use Neem Oil As Organic Pest Control
5. Remove Gnat Infested Soil
Remove the top inch of soil and replace it with fresh, sterile, and dry potting mix. This will get rid of most of the fungus gnat eggs, larvae, and pupa, and make it easier for you to gain the upper hand.
Just keep in mind that the eggs could still hatch and mature after you remove it from your houseplant, so make sure you take the infested soil outside to the trash right away.
6. Use Soil Covers
Rather than refreshing the top inch of soil, you can add a dry layer of fine sand, gravel, or crushed granite instead. This will help deter the females from laying eggs. Plus it creates a nice decorative touch.
Or you could try a barrier top dressing, which is a non-toxic product that is specifically made for eradicating fungus gnats.
7. Store Unused Soil In A Sealed Container
Bags of potting soil can become a breeding ground for fungus gnats. So it’s important to store any of your unused mediums in sealed containers, especially if you keep them inside the house.
8. Never Reuse Potting Soil
I know it’s tempting to pinch pennies by reusing soil when you repot your indoor plants or after one dies, but you’re just asking for trouble.
Used soil can harbor all sorts of pests and diseases, and can quickly cause an infestation. So it’s always best to use a fresh, sterile mix, and discard the old stuff.
Related Post: Natural Pest Control Remedies For Houseplants
Treating the soil with hydrogen peroxide may work to kill fungus gnats. Try mixing 1 part hydrogen peroxide to 4 parts water and use it to wet the top inch. Keep in mind that this will only kill the larvae and pupa, and not the adults that are flying around your plant.
While it is possible to get rid of fungus gnats, you have to be diligent with your preventative measures to keep them away permanently. The biggest problem is that they can easily come through window screens and doors. So unless you seal your home year round, it’s possible the fungus gnats will return at some point.
Unfortunately, fungus gnats will not go away on their own. You have to take steps to eradicate them, and also prevent them from coming back. First make sure you’re not overwatering your plants, then treat the soil to get rid of them.
Everyone with indoor plants will have to fight fungus gnats at some point, it’s just a part of life. Recurring problems are difficult to prevent, and it can be very frustrating. Your best defense is to make sure you don’t overwater, properly store unused potting soil, and always maintain healthy houseplants. Watch my web story for more quick tips.
If houseplant pests are driving you crazy, and you want to learn how to get rid of them once and for all, check out my Houseplant Pest Control eBook. It will help you identify common houseplant bugs, and show you exactly how to eradicate them before they kill your beloved plants. Download your copy today!
More About Houseplant Pests
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- How To Get Rid Of Scale Insects On Houseplants
- How To Get Rid Of Whiteflies On Indoor Plants
- How To Get Rid Of Aphids On Houseplants
- How To Get Rid Of Mealybugs On Your Houseplants
Leave a comment below and share your tips for how to get rid of fungus gnats in houseplant soil.