How To Get Rid Of Gnats In Houseplants

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?

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:

  • Egg; like all insects, they lay eggs (this lasts less than a week).
  • Larva; fungus gnats larvae, unlike butterflies, live in the soil, they are long and transparent white (this phase lasts up to 14 days).
  • Pupa; this is when the larva goes through the transformation into adult, like chrysalis for butterflies (a phase of only 3 to 5 days).
  • Adult; the reproductive phase, with wings and legs (even this only lasts less than one week).

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?

Are fungus gnats dangerous to your 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?

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:

  • The size; they are very small. In fact, they go from 2 to 8 millimeters in length.
  • Appearance; they are dark gray or black, they have long legs (close by, they look a bit like mosquitoes) and they have see through wings. They are much thinner and have longer legs than fruit flies. Fungus gnat larvae are transparent; that makes them easily recognizable.
  • Behavior; fungus gnats are not good fliers; fruit flies can fly farther and better, while fungus gnats will tend to stay close to their birthplace, mainly crawling on the ground and flying from nearby branch to nearby branch.

Why do plants get 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

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:

  • Preventing them from coming.
  • Killing them.
  • Repelling them.

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

Preventing gnats from taking home in your house plants

There are a few ways in which you can prevent them from coming:

  • Do not overwater your plants.
  • Do not recycle your potting soil.

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

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.

  • Reduce the quantity of water you give your plants.
  • Slightly lengthen the intervals between each watering.
  • Water your plants from below! Pour the water into the saucer and not on the soil. This will keep the humidity lower down the pot, while the top layer will be drier and fungus gnats need a lot of moisture in the very top of the soil to survive.
  • Empty saucers from excess water.
  • You should aim to allow the soil to become almost but not completely dry before
  • you water again. This is unless they are succulents, in which case, you should always let the soil dry.

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?

Is killing house gnats necessary

While the temptation may be strong, there are three issues with it:

  • Fungus gnats are not even pests, and killing them sounds a bit excessive.
  • It is not actually necessary, as there are alternative ways of getting rid of them.
  • The methods used to kill them may damage your plants.

How to Get Rid of Fungus Gnats In Houseplants

1: hydrogen peroxide To Get Rid Of Fungus Gnats On A House Plant

Getting rid of gnats the harsh way: hydrogen peroxide

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:

  • Make sure the top soil is dry.
  • Mix 3% hydrogen peroxide in water.
  • Water the plant with the mix.

This will kill the larvae, allegedly, and many people recommend this method. However, there are four major issues:

  • Hydrogen peroxide is produced chemically.
  • High concentrations of hydrogen peroxide can damage plants. At 10% it is actually used as a weed killer. Note that your pot will not be able to get rid of it as easily as happens in full soil.
  • It also kills useful organisms in the soil and, as we said, plants spend on them to be healthy.
  • While many people swear that it kills larvae, it appears that it only irritates them, at least, when you put a drop of hydrogen peroxide directly on them they writhe and run away but do not die.
  • From a more advanced and holistic perspective, H2O2 (that’s the formula) is a chemical signal that plants give off when they are under stress. Considering how plants pick up these signals as a form of communication, I would think that pouring it into their pot is like “shouting scary words” to them.

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

Getting rid of gnats the harsh way (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.

  • You can put flypaper in the saucer or around the pot.
  • Alternatively, people use a plastic plate as saucer and fill it with wet glue (glue sticks you use for paper or those little bottles whose brand we don’t need to advertise).

This method has also three major disadvantages:

  • You need to keep changing the sticky trap, or keep dead corpse in full sight at home.
  • It may catch some adults, but many will survive and it only takes one to start the colony again.
  • It only catches adult gnats. The larvae will keep turning into winged insects and buzz around your living room.

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

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

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?

  • Simply add about ½ inch (1 cm) of sand on top of the soil.

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:

  • Remove 2 inches from the top soil and replace it with a lower layer of potting soil and one of sand.

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

Getting rid of fungus gnats the nice way: 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:

  • They are totally organic.
  • They are innocuous to Humans and pets (with some exceptions, but this is not our case).
  • They do not harm plants.
  • They are a gentle but efficient way of getting rid of insects and other plant problems (molds, fungi etc.)
  • They smell nice.
  • You can also use them for other purposes (from aromatherapy to making your own beauty products).

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:

  • Cedar wood essential oil
  • Eucalyptus essential oil
  • Geranium essential oil
  • Patchouli essential oil
  • Peppermint essential oil
  • Rosemary essential oil
  • Tea tree essential oil

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…

  • Fill a spray bottle with water.
  • Add a few drops (depending on the size of your bottle, but 5 to 10 drops per liter are fine) of your chosen essential oil.
  • Shake well.
  • Spray the plants, soil and pots.

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.

2 thoughts on “How To Get Rid Of Gnats In Houseplants”

  1. Yeah, I bottom water to begin with and have moved on to fans, sand, a metric ton of sticky traps, apple cider vinegar traps, diatomaceous earth, BT, replacing the top soil on everything I could manage, and fungus gnats have absolutely laid waste to huge swaths of my seedlings, baby plants, and a white sage I brought in for the wet Seattle winter. I’ve been fighting this for weeks at this point – I think I must have gotten a contaminated bag of soil and it spread to all my other plants before I realized what was happening. So, maybe this is an easy problem to solve if you don’t live somewhere as wet as here and aren’t dealing with 15 trays of destroyed seedlings and two months of work? Just really frustrated and wanted to note that your, “fungus gnats are totes easy to fix and don’t do any real damage anyway,” tone to be dismissive and hurtful. I’ll continue to look up more essential oil info, since you don’t really give details on potential damage to seedlings.

    Reply

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