One day you see one; the next day a small group… A week on, your house is swarming with many tiny, black flying insects…
That’s what happens if you are not careful with fungus gnats, also known as soil gnats.
One of the most common problems with houseplants, soil gnats can be a real nuisance… You don’t want them flying all over the place, do you?
Fortunately, they are totally innocuous to Humans and you can easily get rid of them. And this is exactly what we are going to talk about.
So, how do i get rid of gnats in my potted plants?
There are many ways of preventing fungus gnats as they are pretty vulnerable little insects. The best way to get rid of gnats in indoor plants is with a multiple approach: reduce and change the way you water your potted plants, remove the top soil and put a layer of sand on top of it to remove the larvae and finally use some essential oils to make sure the adults leave and don’t come back.
Read on and you’ll find out all about fungus gnats, how they live, how you can recognize them but also how to how to get rid of them and prevent them from coming and how to send them packing if they do.
What are fungus gnats?
Fungus gnats, also known as soil gnats appear as very tiny, dark flies, only a few millimeters long.
They are of course winged and slim in appearance. From a scientific point of view, they are not a species, but many different ones from six families: Bolitophilidae, Diadocidiidae, Ditomydiidae, Keroplatidae, Mycetophiliiae and finally, in alphabetical order, Sciaridae.
This may not mean much to you, but just take away the point that the term “fungus gnat” is more a gardening one than a zoological definition.
Still, they all have something in common and the clue is in the name: they feed on organic matter found in the soil, including rotting leaves, and, of course, fungi.
Their lives are short, and they are in four phases, as typical with insects:
As you can see, their whole life cycle is shorter than a month. Unfortunately, this also means that they reproduce very fast.
Are fungus gnats dangerous to Humans?
I am pleased to tell you that they are only an inconvenience. In fact, they don’t bite, don’t carry disease and totally ignore us. No danger for you, your family or even your pets then!
Are fungus gnats dangerous to your Indoor plants?
Even in this respect, fungus gnats do not pose a threat to your potted plants. They usually do not damage plants at all, as they simply feed on the organic matter in the soil.
It does happen though that the larvae do gnaw away at some tiny roots, but nothing that can threaten your plants.
However, some of them may carry the spores of Pythium on their feet; this is a genus of a parasitic water mold that can kill young seedlings as soon as they germinate with a condition called damping-off.
Basically, the young stems become toughen and stop growing.
Only some species from the Sciaridae family are actually dangerous to some mushrooms, as they can make the leathery and stunt their growth.
How can you recognize fungus gnats?
Many people tend to confuse fungus gnats with fruit flies. There’s a huge difference though; fruit fly larvae grow up, you guessed, inside fruit.
Fungus gnats are far less likely to find your home a suitable breeding ground for them, though they may come to visit you, especially if you have ripe fruit that they may want to use as a “nursery”…
If you are in doubt, there are three indicators that can help you recognize fungus gnats:
Why do plants get fungus gnats?
This question needs a twofold answer. On the one hand, fungus gnats are very small animals that lay many eggs, so, it is easy for them to enter any place in search for a good place to call home.
But there is another, and more preventable cause of fungus gnats in houseplants, and, like with many other plant issues (root rot, for example) it has to do with watering.
These cute little creatures in fact like to feast on moist organic matter. The more abundantly you water your plants, the more likely you are to have these unwanted guests.
Soil that is particularly rich in organic matter is also more likely to attract these prolific insects.
To be honest, they do sometimes pose a problem also with plants that grow in soil that is less rich in organic matter, like succulents and cacti, for example.
Still, the more organic matter you have in your pot, the more they will find it appealing.
Solving the problem of fungus gnats
I bet you are thinking, “But is there a solution?” Fortunately, there isn’t just “a solution” but a series of solutions and they are very cheap and easy.
Solutions are meanly of three types:
While the first solution is often neglected, the second is a bit drastic and unnecessary, and the third is, in my view, the safest, most ethical and even most pleasurable solution.
Preventing gnats from taking home in your house plants
There are a few ways in which you can prevent them from coming:
With succulents you can even cut their food supply drastically, taking “off the shelves” their favorite meal, fungi, by sprinkling a bit of organic activated charcoal in your posting soil.
This prevents fungal growth, so, your pot will fall down the list of favorite places to take up as nesting grounds…
This is not advisable with plants that need more symbiosis with mycorrhiza to grow.
In fact, fungi and plants collaborate enormously underground; we now understand that roots work in symbiosis with many microorganism and fungi to absorb nutrients.
Taking fungus gnats as a sign of overwatering
Before moving to drastic measures, we should learn from what Nature is telling us with the presence of gnats: we may well have overwatered the plants.
If we look at the problem from this perspective, we can even see fungus gnats as our friends. No adult plant dies from these tiny creatures, but loads die from overwatering.
So, let’s take it as if fungus gnats were telling us that we are killing our plants with overwatering.
The first thing you need to do if you have fungus gnats is reduce watering.
This alone will, in a short time, get rid of most of the gnats. It will also reduce the population of larvae, so, it is a medium to long term solution.
Is killing house gnats necessary?
While the temptation may be strong, there are three issues with it:
How to Get Rid of Fungus Gnats In Houseplants
1: hydrogen peroxide To Get Rid Of Fungus Gnats On A House Plant
This is an old-fashioned way of dealing with fungus gnats in the houseplants soil, deriving from that long history of deviation into “industrial” (or chemical) farming which, fortunately, we are now getting out of. If you are organically inclined, do skip straight to the next section if you want.
Her’s how to use hydrogen peroxide to get rid of fungus gnats on a house plant:
This will kill the larvae, allegedly, and many people recommend this method. However, there are four major issues:
So, if you want my advice, I would definitely not use this method, common though it is. It smacks of a “quick fix” and chemical at that, but the devil is in the detail, and we don’t want to repeat the mistakes of the past.
2: sticky tape and similar methods
This can be an organic solution, but still it involves giving them quite a horrible death. It is based on the same concept as flypaper.
This method has also three major disadvantages:
This too, therefore, is a method I would advise against; it is inefficient as well as messy and cruel.
3: Getting rid of gnats by removing the top soil
Why kill all the adults when you can just “evict” the larvae? Yes, the good news is that they only live in the first inch or so of soil from the surface. In fact, they do not burrow deep into the ground.
This means that you can simply remove about 2 inches of the top soil and replace it with some new potting soil.
This is feasible with many plants without even having to repot them.
If you are so inclined, you may even put the old soil in a garden or park and give the little creatures a second chance. No remorse, no hassle, no chemicals involved.
This method can be a good first measure which, if combined with reduced watering, may well just do the trick.
Still, it may not be fully effective, as you may miss some eggs if you can’t dig deep enough. It is still worth a try though.
4: Getting rid of fungus gnats with sand
Yes, you heard me right… just sand! This method is so simple, cheap and effective that it is fast becoming a favorite with many gardeners, growers and even people who just have a few potted plants by the settee. How can you do this?
That’s it. How does it work though? The sand simply dries too fast for fungus gnats to breed in it. It basically stays dry all the time and the larvae just cannot live in it.
In fact, it may even be a form of prevention if you are worried about your plants. If you want to splash out, add a full inch of sand (2 cm approximately)…
If you want to combine this method with the previous one, you will get a much better result:
The only drawback with this system is that you will have to top the sand up every now and then. This is because it will penetrate down into the after some time. Still, it only takes a minute.
And you can add a splash of color to your potted plants while you’re at it…
5: use essential oils
Essential oils are fast becoming a favorite organic method of pest control.
In recent years, we have seen these nice smelling natural oils applied to many types of pests and unwelcome guests.
So much so that we know exactly which oils work for which insect, fungus or other problem.
They, in fact, have many advantages:
Using essential oils works on the principle that some plants naturally repel some insects. This is harnessing Nature rather than fighting against her.
They are repellants rather than killers, but in the end, what you want is to get rid of them, and they do it perfectly well.
Luckily enough, fungus gnats are very sensitive little beings; this means that there are many, but really many, aromas you can choose from.
You can, in fact, choose any of the following, according to your own personal taste:
The range of oils you can choose from also means that you are more likely to find one that fits the purpose in your cupboards as well on the shelves of your local herbalist.
In fact, unless you use internet shopping, the main issue people have with essential oils is finding them. This depends very much on where you live, in fact.
How can you use them though? Nothing could be easier…
Fungus gnats will simply find the place unbearable and leave. It’s as simple as that. You can even use them to prevent them from coming if you want.
If you then want a longer effect, you can just use a piece of wood (sandalwood or fir are quite common) and put a few drops of your essential oil of choice on it.
Just place it in the pot near your plant and it will release the aroma very slowly, keeping these tiny winged animals away.
The best way to get rid of fungus gnats
I think a multiple approach of prevention and a few easy steps to send them packing if and when they come is the best solution.
Change your watering routine and water from below; remove the top soil and add sand on top; use essential oils to tell them kindly that they are unwelcome and they will just follow your lead and go.
The best way of looking at these tiny, though maybe inconvenient, guests is as a distress signal your plants would like you to pick up. Your watering skills need improving.
They are no threat to anybody, but if you don’t want to have them flying around (and into your glass, who knows why, they tend to do it), then the solution is simple and effective, but it does not need to be violent or harsh at all.
And if you learn your lesson, you will also gain the gratitude of your beloved houseplants.
Amber Noyes was born and raised in a suburban California town, San Mateo. She holds a master’s degree in horticulture from the University of California as well as a BS in Biology from the University of San Francisco. With experience working on an organic farm, water conservation research, farmers’ markets, and plant nursery, she understands what makes plants thrive and how we can better understand the connection between microclimate and plant health. When she’s not on the land, Amber loves informing people of new ideas/things related to gardening, especially organic gardening, houseplants, and growing plants in a small space.