Fungus gnats are an annoying and well-known problem among hobby gardeners and flower lovers. The black, small flies in the potting soil can become a real nuisance within a very short time. A small infestation of flies hardly harms the plants, but if they multiply, the roots can die and start to rot, which often results in the death of the plant.
But where do the small flies in the potting soil come from? The eggs of the fungus gnat are often already contained in the potting soil you buy and you bring the pest into your home. Organic and humus substrates in particular are often infested, as they provide the perfect breeding ground for fungus gnats. Here you can find out how to combat the pests with home remedies.
Fungus gnats in the potting soil: These are the symptoms
In nature, fungus gnats help to decompose rotting plant matter on the forest floor. Because they are very successful at this and reproduce very quickly, they are dangerous for indoor and greenhouse plants. Infested plants are characterized by weak growth and hollow stems. In addition, many small midges fly around the plants and seedlings and seedlings in particular wither quickly.
Prevent fungus gnats
Fungus gnats like it moist. To prevent them, it is important to deprive them of the basis for laying their eggs. You should therefore water your plants a little more sparingly and avoid waterlogging. Only water them when the potting compost has dried out and only water particularly thirsty plants via the saucer. If there is water in the saucer, leave it there for 20 minutes and then pour it away. It can also be helpful to use substrates without soil or to switch your plants to hydroponics.
Because store-bought potting soil is often the cause of fungus gnat infestation, there are a few things to bear in mind when storing it. You should store the potting soil in a cool, dry place and keep the container closed. Also cover it with a tarpaulin to contain any infestation. To be on the safe side, you can sterilize the purchased soil before use.
You will need an oven to sterilize the potting soil. Preheat it to 85 °C, spread the soil out on a baking tray and place the tray in the oven for 30 minutes. The substrate can then be used without hesitation. As an alternative to the oven, the soil can also be heated in the microwave for 30 seconds.
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Home remedies against small flies in potting soil
There are numerous methods that are supposed to help against the small insects, but only very few are really effective in combating them. Insecticides are not always the best choice, as they can also cause damage to human and animal health. There are a few home remedies you can try before resorting to chemicals:
Bird sand
An effective way to combat fungus gnats is to sprinkle the soil with a layer of bird sand. This should be at least one to two centimeters thick and kept dry. The sand draws moisture from the soil and prevents egg laying, as the surface is closed but breathable.
Tights for covering
Another way to prevent the little flies from laying their eggs in the potting soil is to cover it with tights. This prevents the fungus gnats from reproducing and they slowly die out.
Baking powder
Baking soda is a real all-rounder in the household and can also be used to control flies in potting soil. Sprinkle it on the potting soil and then spray it with a little water. The baking soda is now absorbed into the soil and is eaten by the larvae, which die due to the ingredients. Depending on the severity of the infestation, the treatment may take a little longer and must be repeated several times. However, it is gentle on the plant and very inexpensive.
Vinegar
Vinegar is also an effective household remedy against fungus gnats. Place a bowl of vinegar, water and washing-up liquid in a ratio of 1:1:1 next to the plants infested with the small flies. The animals are attracted by the smell of the vinegar and eventually drown because the detergent releases the surface tension of the water.
Kitchen herbs
Kitchen herbs such as parsley and chives are good for getting rid of small flies in the potting soil. The essential oils they contain repel fungus gnats and thus prevent them from laying eggs in the soil. To do this, chop the parsley into small pieces and spread it over the potting soil or place pots of fresh chives between the infested plants. Because the parsley dries out at some point and loses its fragrance, it must be sprinkled again and again.
Never oil
Niemöl 🛒 is obtained from the seeds of the niem tree and acts as a kind of natural poison on the larvae of the fungus gnat. The active ingredient azadirachtin influences the hormone balance of the larvae so that chitin formation is disrupted. Mix the oil with water in a ratio of 1:100 and add a little washing powder. Then moisten the soil of the infested plants with the mixture.
Beneficial insects
If your plants are suffering from a very heavy fly infestation, nematodes are usually the last biological solution. These are beneficial insects that eat the eggs of the fungus gnat. They are harmless to the plant as well as to humans and animals. Nematodes (Steinernema feltiae) or bacteria (Bacillus thuringienses) are particularly suitable because they reproduce immediately and offer good long-term protection for the potting soil. You can easily administer them via the irrigation water.
Less suitable household remedies are matches, garlic, cinnamon or coffee grounds, as their effect is often too weak or they even exacerbate the problem because they cause the potting soil to become compacted and start to mold. You should also stay away from tea tree oil, as it damages the roots of the plants and they have already suffered enough from the infestation.
If you can’t get the infestation under control despite home remedies, you can of course also use chemicals or the classic yellow boards 🛒. The small flies stick to them and eventually die. This means that flies can no longer lay eggs in the potting soil and your plants can recover. However, when using chemicals, make sure that the plants are not within reach of your pets and children to avoid damage to their health.
Sources: focus, plantopedia
