They seem to appear out of nowhere and quickly become a nuisance: black flies in the potting soil. There is a lot of advice that should help against the insects. But only very few measures combat the pests effectively.

Sticky traps are a helpful weapon in fighting fungus gnats

Table of Contents

Show all
  1. the essentials in brief
  2. recognize flies
  3. get rid of flies
  4. Recommended home remedies
  5. Prevent an infestation
  6. frequently asked Questions

    7. the essentials in brief

    • Small flies in the potting soil are almost always fungus gnats.
    • A heavy infestation can damage the plant as the flies feed on the roots.
    • Fungus gnats can be fought with carnivorous plants such as butterwort, nematodes, predatory mites or by covering the potting soil.
    • Good home remedies for fungus gnats are: coffee grounds, neem oil, tea tree oil, baking soda or vinegar.

    Which insects live in the potting soil?

    The little flies that crawl out of the potting soil are fungus gnats. The insects prefer a humid microclimate and lay their eggs on humus-rich soil. The larvae live in the substrate and feed on plant roots. A small infestation does not harm the plant. However, the roots can die and begin to rot. Fungal spores find an optimal breeding ground here.

    Look

    Fungus gnats vary in size depending on the species. There are mini fungus gnats that grow to a length of one millimeter, while other representatives of this genus reach a body size of seven millimeters. Their slender body and wings are dark in color. In some species, the females are wingless. The greyish to white larva has a slender body and a black head capsule protected by a chitinous sheath.

    development

    After the females have laid their eggs, the first larvae hatch within the next five to eight days. They live sociable in groups that can contain up to 2,500 individuals per square meter. The larva spends the next 14 days in the substrate and goes through several stages of development before pupating. After another seven days, the adult insect hatches, which has a lifespan of five to seven days.

    Fruit flies in the potting soil?

    It is a myth that fruit flies also lay their eggs in the substrate. These insects have specialized in other habitats. Females attach their egg packets to fruit, preferring citrus fruits and decaying or fermenting organic material. The larvae feed on bacteria and other microorganisms attached to the shell.

    Flies in the potting soil - what helps against it?

    If the infestation is still in its early stages, you should first eliminate the adult insects. If the fungus gnats have become a nuisance, take further action. It is always better to use several methods at the same time.

    cover earth

    The first measure to contain the infestation is to cover the bare soil. The adult fungus gnats need access to the ground because this is where they lay their eggs. If you cover the soil with a layer of sand or pebbles, the insects can no longer get onto the substrate. This eliminates the risk of further spread.

    Butterwort

    If the infestation is not that severe, you should place some planters with butterwort between your indoor plants. Butterwort (Pinguicula vulgaris) is a plant native to Central Europe that is extremely easy to care for. It belongs to the carnivorous plants and magically attracts flying insects. Once these settle on the sticky leaves, they can no longer escape. Fatty herbs are a natural and aesthetic alternative to glued yellow boards.

    In principle, all carnivores are suitable as natural traps. However, you should favor plants that can grow in a drier environment. Otherwise there is also a risk that the fungus gnats will lay eggs in the substrate. To be on the safe side, also cover the soil with small stones for the carnivorous plants.

    Suitable carnivorous plants:

    • Mexican Butterwort (Pinguicula moranensis)
    • Apple Butterwort (Pinguicula alpina)
    • Round-leaved sundew (Drosera rotundifolia)

    Butterwort magically attracts fungus gnats

    nematodes

    If the infestation is severe, the larvae in the substrate can be fought with nematodes. The nematodes live parasitically and bore into the body of the larva in order to eat them from the inside. The most popular beneficial in this group is the species Steinenerma fetiae. In greenhouses, Heterorhabditis bacteriophora has been shown to be more effective. Once the sciarid larvae have been destroyed, the nematodes will also die.

    Application:

    • give to the earth immediately after purchase
    • moisten the substrate
    • repeat if necessary

    predatory mites

    This biological weapon is used in a manner similar to nematodes. They kill the larvae of fungus gnats and are recommended for heavy infestations. Predatory mites only die when there is no more food available. Since they do not specialize in any prey, they are used for general pest control. They prove extremely useful when your plants are infested with multiple pests. After about seven to ten days, the beneficial insects have defeated the plague.

    A word on chemical combat

    Chemicals effectively destroy larvae and imagos. However, the products also endanger numerous other insects and beneficial insects. If the ingredients get into the ground or groundwater, environmental damage cannot be ruled out. Since the chemical club also affects health, such agents have no place in the house and garden.

    Recommended home remedies - ask Mutti

    Home remedies are the first choice when it comes to fighting fungus gnats and other plant pests. However, keep in mind that any remedy can harm the plant. Non-natural substances always pose a risk and also affect the microfauna in the substrate. Therefore, home remedies should only be used with caution and extremely sparingly.

    digression

    How do yellow boards work?

    Yellow boards are made of cardboard or plastic and are - as the name suggests - colored yellow. They are coated with a liquid glue so that the insects that land can no longer fly away. The toxic effect of the glue is extremely low, so that there is no health risk when it comes into contact with crops. Many of these adhesives are also used for branded fruit labels.

    Numerous insects such as fungus gnats are attracted to the color yellow. However, yellow boards are not suitable for pest control, since not all animals are caught. Insects are always spared, which can continue to mate and produce offspring.

    neem oil

    Neem oil repels fungus gnats and other pests

    The oil from the seeds of the neem tree acts as a natural poison because it prevents the formation of chitin and thus inhibits the development of the larvae. Responsible for this is the substance azadirachtin. This negatively influences the hormonal balance of the insects. Prepare a 1:100 oil-water solution and add some washing powder to the mixture. You can then use this to moisten the soil. So that your plant is not damaged, you should use the mixture extremely sparingly. It helps with an advanced to severe infestation.

    coffee grounds

    In the case of an acute infestation, you can water your plants with freshly brewed coffee every day for two weeks. This method is not suitable for plants that prefer alkaline soils. Alternatively, you can also sprinkle some coffee grounds on the substrate. Coffee is not only considered a preventative against pest infestation, but also has fertilizing properties. Nutrients such as nitrogen, potassium and phosphorus support root growth and promote flower and seed formation. Fungus gnats are deterred by the intense aroma.

    You should pay attention to this:

    • Allow coffee grounds to dry to avoid mold growth
    • only suitable for plants that grow in rather acidic soils
    • give in small amounts

    baking powder

    The leavening agent proves effective in destroying insect larvae. Sprinkle the powder onto the potting soil and dampen the substrate with water from an atomizer. If the larvae eat the powder, they die after a short time. It may be that you have to repeat the treatment several times before you see success. However, baking soda does not harm the plants.

    tea tree oil

    Tea tree oil has antibacterial and antifungal properties. Because of its very strong antimicrobial effect, it is preferably used for pest control. Mix 20 drops of the essential oil in a liter of water and water your plants sparingly with the solution. Tea tree oil is useful for killing the larvae when the infestation is more advanced.

    kitchen herbs

    Many insects and their larvae do not like the smell of essential oils. Therefore, spices and kitchen herbs are ideal for scaring away the annoying little animals. This method mainly deters adult insects from laying eggs in the substrate. The larvae do not die from this. Once the scent of the herb wears off, the method needs to be repeated.

    plant parts used application
    Parsely chopped herb sprinkle regularly on the ground
    chives entire plant Distribute planters between houseplants
    garlic toes stick in the ground

    vinegar

    Fungus gnat images are attracted by the intense vinegar aroma. Pour 125 milliliters of vinegar into a container and place it next to the affected plants. To increase the attraction, you can put pieces of potatoes or apples in the container. The disadvantage of this method is the odor nuisance.

    Trap types to build yourself:

    • lid trap: Cover the container with cling film and pierce it with a nail
    • sink trap: Add a drop of dish soap to the vinegar to reduce surface tension
    • sticky trap: coat a piece of plastic with glue and vinegar

    Matches - a myth

    The belief that matches can kill insect larvae in potting soil persists. Potassium chlorate and sulfur are present in the heads. This combination is said to have a deterrent effect on the adult insects and kill their larvae. The imagos can be chased away with a lit match, at least for a short time.

    To kill the larvae, stick the sticks upside down in the substrate and replace them every two to three days. In practice, however, this method has not proven itself. If you still want to try it, you should only use the matches on robust plants.

    Prevent an infestation

    Fighting the insects with just one remedy usually only provides a temporary remedy. If the living conditions are right, fungus gnats will settle again and again. Targeted prevention is therefore necessary.

    heat earth

    Potting soil is often already interspersed with eggs or the fungus gnat larvae live in the substrate of indoor plants. To be on the safe side, you should heat the soil in the oven or in the microwave before putting it in a planter. Spread the substrate out on a baking sheet, set the oven to the highest temperature and heat the soil for at least ten minutes.

    tips

    The larvae die in the substrate if you keep the houseplant dry for some time - provided your plants are not sensitive to longer periods of drought.

    Regulate room temperature

    Fungus gnats like warm conditions, so they prefer to spread during the heated winter season. Make sure the room temperature is not too high. The thermometer should fluctuate between 18 and 20 degrees Celsius. If your indoor plants are not particularly sensitive to cold, you can also place them in an unheated room.

    tips

    Fungus gnats like a humid microclimate. Make sure that the substrate is not too damp and avoid waterlogging!

    frequently asked Questions

    What to do against black flies in the potting soil?

    The annoying insects like moist conditions in the substrate. Keep the soil dry and do not water the houseplant for a while. If the insects have spread in the soil of moisture-loving plants, flooding will help. Place the planter in a water bath for some time. The larvae die off and the plants don't mind the bath.

    Where do flies in potting soil come from?

    The flies are fungus gnats that lay their eggs on the exposed substrate. Once the larvae hatch, they bury themselves in the ground for further development. Often the flies appear after you have placed your indoor plants on the balcony and they have been infected by free-flying fungus gnats. Bought potting soil or indoor plants from the hardware store can also be infested by the insects.

    Can I protect my plants from fungus gnats?

    You can prevent an infestation by heating potting soil in the oven before using it. Place a tray filled with soil in the oven for ten minutes. At the highest temperature, larvae and eggs are killed. However, the earth is completely sterilized by this measure, so that the natural soil fauna is lost. It is therefore better to cover the bare substrate with a layer of sand. In this way, flying insects have no access to the ground and are prevented from laying their eggs.

    Are there home remedies for fungus gnats?

    The common home remedies that hobby gardeners use against plant pests also help against fungus gnats. However, you should also use these agents with caution so that your plants are not damaged. Coffee has proven to be effective in getting rid of the plague. A gentler variant are kitchen and aromatic herbs such as chives, parsley and garlic. Their aromas repel insects and larvae.

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Care tips