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The flower pot is not only a suitable habitat for many plants, but also a breeding ground for numerous pests that like to attack the plants. As soon as a swarm of small, black flies rises from the pot during watering, the larvae of the fungus gnats have nested in the potting soil and are happy to eat the fine roots. The right care and suitable home remedies work wonders against the robust pests.

fungus gnats

What are fungus gnats?

The fungus gnats (Sciaridae) are a family of mosquitoes that occur in Europe with over 600 species and, unlike their relatives, the mosquitoes, are not interested in human blood. They can be recognized by their slim build and deep black coloration, although there are a few exceptions. On average, they are between one and seven millimeters long, so tiny to the naked eye. Despite their small size and short lifespan of a maximum of five days, they can cause a lot of damage, as the females can lay over 300 eggs in the potting soil.

  • Fungus gnat larvae have an easily recognizable glassy-grey body of 5-10 mm
  • feed on decaying plant tissue and fresh, fine roots
  • remain in the flower pot for about 20 days until further development
  • Pupa is yellow-brownish
  • Males have wings, females do not
Fungus Gnat, Sciaridae

After the flies are past their pupal status, they reproduce and the whole cycle starts all over again. If you are not sure whether the flies in the potting soil are fungus gnats, pay attention to the following behavior.

  • dancing, slightly "swaying" flight movements
  • Larvae and pupae are found in or on the surface of the substrate and are easily recognized by their different coloration
  • only stay near plants or compost

They are often mistaken for fruit flies, which have a brown body instead of black and, as their name suggests, will be found around ripe fruit. So if there is a swarm of brown flies near your fruit basket, they are not fungus gnats.


Symptoms of Sciaridae infestation

If you want to fight the flies, you must first check whether they really are infested. Due to their function as a decomposer, an organism that decomposes plant materials, they are the most important representatives of this function in nature alongside the fungi. Especially in the forest, they help to decompose the decaying plant parts on the forest floor. They are extremely successful with it, but this has a negative effect on the maintenance of indoor and greenhouse plants, as they simply multiply too quickly.

Affected plants show the following characteristics:

  • Seedlings and cuttings die
  • weak growth, plants wither
  • hollow stems due to insect damage
  • many mosquitoes fly around the plant

Notice: Young plants in particular suffer greatly from the hunger of the mosquitoes and can perish within a short time, which makes the infestation so dangerous. It is better if you do not even give the insects the opportunity to choose your plants as a feast, because the right prevention deprives the mosquitoes of their food base.


Prevent fungus gnats

In order to effectively combat Sciaridae species, it is important not to provide them with a basis for laying eggs. The most important factor here is the plant substrate, because the larvae need permanently moist soil in order to be able to develop. Therefore, you should do the following to prevent egg laying.

  • only water when the surface of the potting soil has dried
  • water over the saucer for water-thirsty plants
  • if there is water in the saucer, leave it for about 20 minutes and then pour it away
  • cover the surface with a layer of quartz sand lower than two centimeters;
  • Quartz sand extracts moisture from the soil and prevents egg laying because the surface is closed but breathable
  • if possible, switch to hydroponics or special substrates that do not require soil
Fungus Gnat, Sciaridae

These points can save you a lot of work, because as long as the potting soil can breathe and does not become too damp, the healthier your plants will remain. It is particularly important that no waterlogging forms, as this increases the propagation process of the pests. It is always advantageous if you let the surface of the potting soil dry in the flower pot. Store-bought potting soil is often to blame for the infestation, especially organic and humus substrates, as these are the perfect breeding ground for fungus gnats.

Consider the following when purchasing the Earth:

  • store purchased potting soil in a cool, dry place
  • keep the container closed
  • if necessary, cover it with a tarp to contain the infestation

So the flies have no chance to get closer to the earth and lay their eggs in it. However, eggs may already be present in many substrates, as these are plentiful in peat and are therefore included in much of the available soil. For this reason, it is important to sterilize soil before use, especially if it is organically produced, humus-rich substrate.

You only need an oven to sterilize the potting soil:

  • preheat the oven to 85°C
  • Spread the earth out on a baking sheet and loosen it a bit
  • Place the tray in the oven for 30 minutes
  • then you can use the substrate without hesitation

It is also a good idea to check the soil for eggs before sterilizing it. For this you need a yellow sticker, a kind of shield in a yellow tone that has adhesive surfaces. The color magically attracts the mosquitoes and they then stick to the sticker.

Test the potting soil as follows:

  • take a sample of the freshly acquired soil
  • place them in a small flowerpot along with the yellow sticker
  • moisten them heavily
  • place a close-meshed net with a maximum mesh size of one millimeter around the pot
  • wait three weeks
potting soil

If the earth is already interspersed with eggs, there should be numerous mosquitoes on the yellow sticker after the waiting time. Thanks to the close-meshed net, these cannot escape and therefore do not attack other plants. If flies were discovered, the substrate must be sterilized. Soil for indoor plants makes sense because it has already been sterilized in advance.

Tip: As an alternative to the oven, you can also heat the soil in the microwave for 30 seconds. That works just as effectively.

Effective home remedies

You don't always need chemicals to fight the flies in the substrate. The chemical club can lead to health problems, since the insecticides can also reach people and pets. In addition to the classic yellow boards or stickers, you should use the following home remedies to combat annoying insects.

  • baking powder
  • matches
  • Parsely
  • chives
  • beneficials
  • neem oil
  • vinegar
Use home remedies for fungus gnats

Tip: Coffee grounds, along with alcohol and nicotine, are a commonly recommended remedy for controlling fungus gnats, but the coffee grounds are only marginally effective. Due to the structure, the coffee grounds soak into the substrate over time and begin to compact and mold, which is not ideal when fighting the pests.

baking powder

Baking powder is a remedy that is effective for fighting flies. Since this is not about chemistry, you can use the product on all plants without having to take any health risks. For this you only need baking powder and a little patience, because even if the first application with the agent does not work, the second application is more effective.

Proceed as follows:

  • sprinkle the substrate with the powder
  • use a spray bottle to moisten it
  • then the powder soaks into the ground

After the powder is absorbed, the larvae will eat it and die on the ingredients. Depending on the severity of the infestation, treatment may take some time, but due to the low cost, you can get a large quantity of the powder for a few bucks. The motto here when fighting flies is perseverance and you should change the powder at regular intervals.

Use baking soda as a home remedy


Matches are an effective way to get rid of those pesky flies. They contain potassium chlorate in their heads, which is extremely aggressive to the larvae. You can also use the matches to scare away the adult males by lighting a match near the plant. The smell drives them away and they avoid the plant for a while. To fight the larvae with the sticks, all you have to do is stick their head into the ground and wait. The potassium chlorate moves into the potting soil and gradually kills the larvae. This method is not suitable for sensitive plants, as excessive amounts of potassium chlorate could damage them.

Matches as home remedies


Parsley is a popular culinary herb and is surprisingly good for fighting fungus gnats. All you need is fresh parsley, which you cut into small pieces and spread on the surface of the potting soil. Due to the essential oils contained, the adult mosquitoes in particular avoid the equipped plant and therefore do not produce any offspring. Here you just have to make sure that the effect decreases as the scattered parsley dries up and you have to sprinkle it again and again. So stock up on the herb.


Chives act like parsley for controlling, but are more suitable for plants that are in flower pots in the greenhouse. Since the temperatures in the greenhouse are different, the essential oils and ingredients work better here and protect the potting soil more effectively from the pests. However, this is not cut into small pieces, but placed in the immediate vicinity of the infested plants or in large numbers in order to drive away the insects with their smell. Chives always grow back in this state, so you not only fight the flies, but you can also enjoy the taste of the herb.

Chives in the herb bed


To combat the fungus gnats, there are appropriate beneficial insects that specifically attack the larvae and kill them. They include those listed below.

  • Threadworms (nematodes) Steinernema feltiae: works between 12°C and 30°C within three weeks
  • Bacterium Bacillus thuringienses: works at any temperature within a few days

While the nematodes are actively chasing the fungus gnat larvae, the bacteria spread via spores inside the pot and produce proteins that are poisonous to the flies. The nematodes, on the other hand, feed on the body fluids of the larvae and these die off as a result. Both beneficial insects are biologically and ecologically harmless and have no effect on people, animals and the plants themselves. Both beneficial insects even multiply and provide long-term protection for the potting soil. They are administered via the irrigation water.

neem oil

The oil from the neem tree, more precisely the seeds, acts as a natural poison against the formation of chitin in the larvae. The reason for this is the substance azadirachtin, which has a negative effect on the hormonal balance of the fungus gnat.

The oil is used as follows:

  • mix the oil with irrigation water in a ratio of 1:100
  • add soap nut powder
  • shake the emulsion vigorously
  • use the household remedy as irrigation water or with a spray bottle


Place a bowl filled with vinegar, water and washing-up liquid in a ratio of 1:1:1 next to infested plants. Flies are attracted to the smell of vinegar and die due to the surface tension released by the detergent. They eventually drown.

Vinegar as a home remedy

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