They seem to arise from nothing and quickly develop into a nuisance: black flies in the potting soil. There is a lot of advice to help against insects. But only very few measures effectively combat the pests.
How to get rid of flies in potting soil?
To combat flies in the potting soil, fungus gnats can be treated with home remedies such as coffee grounds, neem oil or tea tree oil. Alternatively, carnivorous plants such as butterwort can be used or the soil can be covered with sand or pebbles to prevent egg laying.
Which insects live in the potting soil?
The little flies that crawl out of the potting soil are fungus gnats. The insects prefer a moist microclimate and lay their eggs on humus-rich soil. The larvae live in the substrate and feed on plant roots. If the infestation is small, this will not harm the plant. However, the roots can die and begin to rot. Fungal spores find an optimal breeding ground here.
Appearance
Sad gnats grow in different sizes depending on the species. There are mini fungus gnats that are one millimeter long, while other members of this genus reach a body size of seven millimeters. Their slender body and wings are dark colored. In some species the females are wingless. The grayish to white larva has a slender body and a black head capsule protected by a chitinous cover.
Development
After the females lay their eggs, the first larvae hatch within the next five to eight days. They live gregariously 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 developmental stages until it pupates. After another seven days, the adult insect hatches and 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 packages to fruit, preferring citrus fruits and decaying or fermenting organic material. The larvae feed on bacteria and other microorganisms that adhere to the shell.
Flies in the potting soil – what helps against it?
If the infestation is still in its early stages, you should first remove the adult insects. If the fungus gnats have developed into a nuisance, take further measures. It is always better to use multiple methods at the same time.
Cover the earth
The first measure to contain the infestation is to cover the bare soil. The adult fungus gnats need access to the soil 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 to the substrate. This eliminates the risk of further spread.
Fedwort
If the infestation has not yet progressed so badly, you should place a few planters with butterwort between your houseplants. The common butterwort (Pinguicula vulgaris) is a plant native to Central Europe that is extremely easy to care for. It is a carnivorous plant and magically attracts flying insects. As soon as they settle on the sticky leaves, they can no longer escape. Butter herbs are a natural and aesthetic alternative to glued yellow boards.
In principle, all carnivores are suitable as natural traps. However, you should prefer 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, cover the soil with stones for carnivorous plants too.
Suitable carnivorous plants:
- Mexican butterwort (Pinguicula moranensis)
- Aplen butterwort (Pinguicula alpina)
- Round-leaved sundew (Drosera rotundifolia)
Fedwort magically attracts fungus gnats
Nematodes
If the infestation is severe, the larvae in the substrate can be controlled with nematodes. The nematodes live parasitically and bore into the body of the larva in order to eat it from the inside. The most popular beneficial insect in this group is the species Steinenerma fetiae. Heterorhabditis bacteriophora has been shown to be more effective in greenhouses. As soon as the fungus gnat larvae are destroyed, the nematodes also die.
Application:
- give it to the earth immediately after purchase
- Moisten the substrate
- repeat if necessary
Predatory mites
This biological weapon is used in a similar way to nematodes. They kill the larvae of fungus gnats and are recommended for severe infestations. Predatory mites only die when there is no more food available. Since they do not specialize in prey, they are used for general pest control. They prove to be extremely useful when your plants are affected by multiple pests. After about seven to ten days, the beneficial insects have defeated the plague.
A word about combating chemicals
Chemical agents effectively destroy larvae and imagos. However, the products also endanger numerous other insects and beneficial organisms. If the ingredients get into the earth or groundwater, environmental damage cannot be ruled out. Since the chemical club also affects he alth, such products have no place in the house and garden.
Recommended home remedies – ask mom
Home remedies are the first choice when it comes to combating fungus gnats and other plant pests. However, keep in mind that any agent can cause harm to the plant. Non-natural substances always pose a risk and also affect the microfauna in the substrate. Therefore, home remedies should only be used carefully and extremely sparingly.
Excursus
How do yellow boards work?
Yellow boards are made of cardboard or plastic and - as the name suggests - are 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 he alth risk when it comes into contact with crops. Many of these adhesives are also used for brand labels on fruits.
Numerous insects such as fungus gnats are attracted to the color yellow. However, yellow plates are not suitable for pest control because not all animals are caught. Insects are always spared and 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. The substance azadirachtin is responsible for this. This has a negative effect on 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. To ensure that your plant is not harmed, you should use the mixture extremely sparingly. It helps with advanced to severe infestations.
Coffee grounds
If there is 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 preventive agent 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:
- Let the coffee grounds dry to avoid mold formation
- only suitable for plants that grow in rather acidic soil
- administer in small quantities
Baking powder
The raising agent proves to be effective in destroying insect larvae. Sprinkle the powder onto the potting soil and moisten the substrate with water from a sprayer. If the larvae eat the powder, they die after a short time. You may have to repeat the treatment several times until you see success. However, baking soda does not harm the plants.
Tea tree oil
Tea tree oil has antibacterial and fungicidal properties. Because of its very strong antimicrobial effect, it is preferred for pest control. Mix 20 drops of the essential oil in one liter of water and water your plants sparingly with the solution. Tea tree oil is suitable for killing the larvae if the infestation is more advanced.
kitchen herbs
Many insects and their larvae do not like the smell of essential oils. Therefore, spices and culinary herbs are ideal for scaring away the annoying little animals. This method primarily deters adult insects so that they do not lay eggs in the substrate. The larvae do not die from this. As soon as the scent of the herb wears off, the method must be repeated.
| plant parts used | Application | |
|---|---|---|
| parsley | small chopped cabbage | sprinkle regularly on the soil |
| Chives | whole plant | Distribute planters between houseplants |
| garlic | Toes | put in the ground |
Vinegar
Imagos of fungus gnats are attracted to the intense aroma of vinegar. Pour 125 milliliters of vinegar into a container and place it next to the affected plants. To increase the attraction effect, you can place pieces of potato or apple in the container. The disadvantage of this method is the unpleasant smell.
Types of traps 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
- Glue trap: coat a piece of plastic with glue and vinegar
Matches – a myth
The belief that matches can kill insect larvae in potting soil is persistent. The heads contain potassium chlorate and sulfur. This combination is said to have a deterrent effect on the adult insects and kill their larvae. The imagos can be driven away, at least for a short time, with a lit match.
To kill the larvae, the sticks are inserted upside down into the substrate and replaced every two to three days. However, this method has not proven successful in practice. If you still want to try it, you should only use the matches on robust plants.
My amaryllis got it – MIDSHIP MOSQUITOES! Aaaaaaaah! Someone recommended putting matches in the damp soil. The sulfur should do the trick. Well let’s see ??✌️… mourning mosquitoes amaryllis matchsticks pests hippeastrum sulfur fight wtf roomgarden pests
A post shared by Stefan | Garden blogger (@parzelle94.de) on Dec 29, 2018 at 8:15am PST
Preventing an infestation
Fighting insects with just one agent usually only provides short-term relief. If the living conditions are right, fungus gnats will colonize again and again. Therefore, targeted prevention is necessary.
Heat the earth
Potting soil is often already riddled with eggs or the fungus gnat larvae live in the substrate of houseplants. To be on the safe side, you should heat the soil in the oven or microwave before placing it in a planter. Spread the substrate on a baking tray, set the oven to the highest temperature and heat the soil for at least ten minutes.
Tip
The larvae die in the substrate if you keep the houseplant dry for some time - assuming your plants are not sensitive to longer dry periods.
Regulate room temperature
Sad gnats like warm conditions, so they prefer to spread during the heated winter period. Make sure that the room temperature is not too high. The thermometer should fluctuate between 18 and 20 degrees Celsius. If your houseplants are not particularly sensitive to cold, you can also put them in an unheated room.
Tip
Sad gnats like a humid microclimate. Make sure that the substrate is not too moist 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 into the soil of moisture-loving plants, flooding can help. Place the planter in a water bath for some time. The larvae die 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. As soon as the larvae have hatched, they hide in the ground for further development. The flies often appear after you have placed your houseplants on the balcony and they have been infected by free-flying fungus gnats. Purchased potting soil or houseplants from the hardware store can also be infected by the insects.
Can I protect my plants from fungus gnats?
You can prevent an infestation by heating houseplant soil in the oven before using. Place a tray filled with soil in the oven for ten minutes. At the highest temperature, larvae and eggs are killed. However, this measure completely sterilizes the earth, 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 earth and are prevented from laying 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 only use these products with caution so that your plants are not damaged. Coffee has been proven effective in eliminating the plague. A gentler option are culinary and aromatic herbs such as chives, parsley and garlic. Their aromas scare away insects and larvae.
