Fungus gnats (also called soil gnats) are probably the most common (and annoying) houseplant pests. So, in this post, I’m going to tell you all about them, and show you how to get rid of them – FOR GOOD!
The worst part about fungus gnats is that they can infest any plant that is growing in soil. Which means, if you have indoor plants, they can get into every one of them.
You will notice these indoor plant bugs crawling out of the potting soil, or flying around your plant when you water or otherwise disturb the soil. Yuck!
They are a very annoying pest, there’s no doubt about that! But the good news is that you can get rid of them, and keep them from re-infesting your houseplants.
What Are Fungus Gnats?
Fungus gnats are tiny black flying bugs in houseplants soil. You will see them crawling around on top of the soil, or flying around your plants
Fungus gnats live and breed in the soil. Adult gnats will lay eggs in the soil, and the larvae (tiny white worms that are barely visible to the naked eye) will feed on roots and other organic matter in the soil.
Fungus Gnats or Fruit Flies?
Fungus gnats look similar to fruit flies, and I have seen many people mistaken a fungus gnat problem with fruit flies.
But they are not the same type of bug. Fungus gnats lay their eggs in moist soil where the larvae will hatch and feed on small roots, fungus and other organic matter in the soil. They have no interest in fruit.
Here’s a quick way to tell the difference…
- If you see tiny black bugs in plant soil, and flying around your plants – those are fungus gnats.
- The gnats that are flying around the fruit, or the garbage disposal in your kitchen are fruit flies.
If you’re still unsure, read about how to tell the difference between the two here, so you can make a positive ID every time.
Will Fungus Gnats Kill Plants?
The short answer is no, fungus gnats will not kill your houseplants. Fungus gnats are mainly just a nuisance and are rarely destructive to the plant.
Sometimes they can cause root damage if the infestation is heavy, but normally fungus gnats only eat rotting roots.
Even though they aren’t a huge problem for your plants, fungus gnats are likely to drive you crazy, right?! I mean, who want gnats flying all over their house? Not me!
So, let’s figure out how to get rid of gnats in plants… but first, it’s important to understand where they came from in the first place, so we can make sure they never come back.
Where Do Fungus Gnats Come From?
A fungus gnat infestation can come from anywhere. The most common ways fungus gnats get into your house are either they’re in the soil of a newly purchased plant, or in a bag of potting mix that you bring indoors.
But fungus gnats can also come in with a plant that was outside during the summer. Heck, they can even fly in through the screen of an open window or door.
How To Get Rid Of Fungus Gnats In Houseplants Soil
Fungus gnats are difficult to eliminate if you have a large number of indoor plants. The adults can easily fly or jump from one plant to the next, laying eggs wherever they find moist soil.
Like fruit flies, the adult fungus gnats only live for a few days. So, once all the larvae are dead, your fungus gnat problem will go away.
There’s no need to resort to toxic synthetic pesticides, fungus gnats can easily be fought using all-natural pest control remedies and methods. Below are the best methods to use to rid your indoor plants of those annoying flying gnats…
1. Control soil moisture
Fungus gnat larvae thrive in moist soil, and they can’t survive in dry soil.
So, the easiest and most effective method of plant gnats control, and ultimately eliminating fungus gnats, is to make sure you never overwater your plants.
Be careful though, you don’t want to allow the soil to dry out completely on most houseplants. Use a soil moisture gauge to help maintain the perfect level of moisture for your houseplants, and get rid of gnats in plant soil.
Indoor plant watering devices also make watering houseplants easier, and help you avoid overwatering so you can get rid of plant gnats.
2. Water plants from the bottom
Fungus gnat larvae live in the top inch of the soil, which tends to stay pretty moist when you water plants from the top.
Bottom watering plants will make it easier to maintain dryer top soil, without risking the overall health of the plant.
To water your plants from the bottom simply pour water into the plants drip tray or cache pot, and allow the plant to soak up the water through the drainage holes.
Never allow your plant to sit in water for too long. Dump out any remaining water after about 30 minutes of soaking.
3. Use yellow houseplant sticky stakes
Putting a yellow sticky trap near the plant is a super safe pest control method that will attract and capture the adult fungus gnats.
This will only be effective to control the adult population, it will not take care of the problem at the source (the larvae).
But yellow sticky traps definitely help to keep the adult fungus gnats from flying around to other plants.
4. Apply organic pest control products
Pour or spray an organic insecticidal soap or a neem oil mixture into the top of the soil to kill gnats in potted plants.
I make my own insecticidal soap by mixing using 1 tsp mild liquid soap to one liter of water.
Neem oil works great to kill houseplant pests, and has a residual effect that helps with prevention. You can buy neem oil here.
These natural gnat pesticide treatments should be effective after a few applications, just take care not to overwater your plants.
Related Post: How To Use Neem Oil As Organic Pest Control
5. Remove the gnat infested soil
Remove the top inch of potting soil and replace it with new, sterile potting soil.
This will remove fungus gnat eggs and larvae, and make it easier to gain the upper hand.
Just keep in mind that gnat eggs in soil could still hatch and mature after you remove it from your plant, so make sure you take it outside to the trash.
6. Use soil covers
Replace the top inch of soil with a layer of fine sand, gravel, crushed granite, or decorative moss.
This will help control gnats in soil, and deter them from laying eggs. Plus they also add a nice decorative touch.
You could also use a gnat barrier top dressing, which is a non-toxic soil cover that is specifically made for eradicating fungus gnats.
7. Store unused potting soil in a sealed container
Open potting soil bags can also be a breeding ground for fungus gnats, so make sure you keep that in mind when storing unused soil.
I store all of my potting soil in buckets that have a tight fitting lid rather than in the bag it comes in. Fungus gnats can’t survive without oxygen.
If you don’t have an air-tight container you can use for storing plant potting soil, I recommend Gamma seal lids. They work with any standard five gallon bucket.
8. Never reuse potting soil
I know it’s tempting to pinch pennies by reusing potting soil for indoor plants, but you’re just asking for trouble. Always use a fresh, sterile potting soil mix when repotting your plants.
FAQs
In this section, I’ll answer some of the most commonly asked questions I get about controlling fungus gnats in houseplant soil. If you can’t find the answer here, ask your question in the comments below.
Will treating the soil with hydrogen peroxide kill fungus gnats?
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 of the soil.
You can either pour it or spray it over the top. Keep in mind that this will only kill the larvae living in the soil, and not the adult gnats that are flying around.
The most important thing to remember for eradicating fungus gnats is to control how much you water houseplants.
Remember, fungus gnats live and breed in moist soil, and overwatering is the number one cause of houseplant gnats.
Even if you are successful in eliminating a fungus gnat infestation from your house, recurring problems are difficult to prevent. The good news is that fungus gnats are one of the easiest houseplant pests to control.
If houseplant pests are driving you crazy, and you want to learn how to get rid of plant bugs 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 kill them before they kill your beloved plants! Download your copy today, and get rid of bugs on houseplants for good!
More About Houseplant Pests
- How To Get Rid Of Houseplant Bugs Naturally
- How To Make A Homemade DIY Fruit Fly Trap
- How To Debug Plants Before Bringing Them Indoors
Leave a comment below and share your tips for how to get rid of fungus gnats in houseplants soil.
J Connett says
I have 45 plants so you can imagine the problem i have had with fungus gnats. Last year there were thousands but i have managed now to get on top of the problem and only have about 5 or so appearing. You need to use a number of things not just one thing. I use hydrogen peroxide 3% one part hp 4 parts waterr. Surface does need to be dry. Works perfectly if you only have 2 or 3 plants but not financially viable if you have a lot of plants. I water my plants with a BTI tablet which did kill a lot off. It kills the larvae before they hatch. Also use yellow stickers which attracts most of the adults. I also spray surface sometimes with neem oil and horticultural soap. Certainly the BTI seems to come out tops for me so trial and error. Bti does need to be regularly repeated though.
Gina says
What’s a BTI tablet, how is it use, and where can i purchase it? Thank you.
Amy Andrychowicz says
Bacillus thuringiensis israelensis, also known as mosquito dunks, and you can get them online or at your local home improvement store.
Tracy Moorehead says
I have a product called BON-Neem. It is a combination fungicide , miticide and Insecticide. Made by Bonide. I got it last year at a garden center I trust. After much searching for an affordable Neem product.
How affective is this. And is the application the same. I am a little confused as to whether or not you still use this in combination With the top inch of soil and replacement method, and if so when it is applied, before or after. You describe spraying the plant in first section before the soil removal. Would it be advisable to spray wnen you take out the first inch , then replace with new soil. I’m in an apt and have very little room for plants , but I do have several.
Amy Andrychowicz says
I’m not familiar with the particular product you mention, so I can’t speak to how to use it or how effective it is. It’s always best to follow the instructions on the label. If you plan to replace the top inch of soil, there’s no need to spray it beforehand. Just make sure to take it outside to the trash right away, because the eggs could still hatch in the garbage can. You can use neem oil as a soil drench after you remove that top 1″, then replace it with a fresh dry layer or use a soil cover.
Tres says
You keep using the term soil drench but no details of HOW to do this.
Amy Andrychowicz says
You simply pour the mixture over the soil as if you’re watering the plant.
Nathalie says
I can’t identify the bug but I would love some help so here’s a description
1. They’re like ovals.
2.there white with black lines going through them however I have seen a dark brown one
3. They’re small so to me they seem like salt moving in dirt but then there are bigger ones.
Pls help identify
Amy Andrychowicz says
My guess is that they could be scale, mealybugs, or aphids. Here’s an article that will give you further help with identifying common houseplant pests.
Frank says
Is there any fungicide that one can use to kill the fungus thus cut off the food supply
Amy Andrychowicz says
Good question, but no. Fungus gnats feed on the organic material in the soil, so you can’t kill them by cutting off their food supply, unless you try hydroponics.
Lola A. says
What is the best soil cover or insecticide to use?
Amy Andrychowicz says
I have a whole bunch of products suggestions listed with links in the post above. 🙂
Deb says
I was going to order the soil barrier top dressing that you recommend but it’s no longer available on Amazon. Are there other barriers or if I use sand how thick do I put sand on the soil? I’ve been struggling with these darn things for months, I’ve used neem oil and after a month of that moved on to peroxide then also added cinnamon to the surface of the soil to get rid of the gnats but so far they keep coming back. I’ve gone through many yellow sticky traps and am now ordering larger packages of those. Any help would be appreciated.
Amy Andrychowicz says
Shoot, bummer they’re out of the gnat barrier. Fine sand is another good option, use it to replace the top 1″ of soil. But keep in mind that fungus gnats thrive in moist/wet soil. So the first line of defense is to ensure you’re not overwatering any of your plants. Most indoor plants are fine if you let the top inch or two of soil dry out, and that’s where the gnats live, so doing that alone usually will at least decrease their population by quite a bit. Also, make sure you don’t have any bags of potting soil laying around in your home. If so, you should store those in a sealed container because gnats can live in there too.
Nikki says
Hi can you use rice husks to cover the top of your soil to prevent fungus gnats?
Amy Andrychowicz says
I’ve never tried this myself, so I can’t say for sure. But, as long as it creates a dense layer of protection over the soil, then it could work to keep fungus gnats out.
Nancy says
Would freezing the soil be an appropriate approach ? I was not aware of how to store the soil ( first time using it ) so when I opened the bag there were a lot of maggots or baby gnats I suppose. I sealed that bad boy up and threw it in the freezer!
Amy Andrychowicz says
Yes, freezing the soil works great! I always store it in the garage during the winter, where it freezes solid, and no more fungus gnats!