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How to get rid of Fungus Gnats with biological pest control?

Having and taking care of plants is mostly only experiencing the real magic that nature has to offer. But nature also has some downsides, little crawling creatures that would like to take advantage of your beautiful plant collection. Fortunately it’s inevitable to never get issues with plagues, it’s an easy way in for most of these creatures. But PLNTS to the rescue! We offer biological pest control for all types of plagues. This makes you able to deal with everything efficiently, without causing any harm to the environment of your plant. Seems like a win-win situation right? In this blog we will cover how to get rid of Fungas gnats. So if you are ready, let’s dive into all the ins and outs!

Fungus gnats

How do fungus gnats damage my plants?

Fungus gnats, or rather the eggs or larvae of the fungus gnats, are often brought in via your new plants or in new potting soil. Eggs or larvae may already be present in the soil and eventually spread to other plants. They can also simply fly in.

Female fungus gnats find potting soil the perfect place to lay their eggs. It is a moist environment, with lots of organic substances where the larvae can grow well. Unfortunately, these larvae are also the biggest problem. They end up doing the most damage to your plants. The youngest larvae mainly eat the algae and fungi in the potting soil, but the older larvae will also target the roots of the plant. When the roots of a plant are affected, the health and resistance of the plant also deteriorate. It will weaken, making it more vulnerable to diseases and fungi. This can eventually lead to a plant that is beyond saving. Of course, nobody wants that!

Fungus gnats

How do I get rid of Fungus gnats?

Felti (Steinernema feltiae)

Felti are microscopically small nematodes that occur in the soil in nature and they are the natural enemy of the fungus gnat. As many as 1200 species live in the Dutch soil alone. These tiny fighters penetrate the larvae of the mourning flies and then excrete a bacterium that kills the larvae within 1-3 days. The great thing is that they do not affect the plants in any way. In optimal conditions, after 1-2 weeks there are fewer or no pests present in your plant(s). That sounds like music to your ears, doesn't it?

Steinernema feltiae

How to use?

It is actually very easy! Follow the following 5 steps and your plants will soon thank you:

  1. Add the bag of saviours to a watering can completely filled with lukewarm and clean water. This sachet is enough for one full watering can, which is about enough for 10 plants. There are five million saviours in one sachet, Wow!

  2. Stir for about 1 minute so that the nematodes are well distributed in the water.

  3. Pour the solution directly on your plants, all around the potting soil. Give as much water as you normally give to your plants.

  4. Keep the soil moist for another two weeks, so that the nematodes do not dry out. They also need water/moisture to move through the potting soil.

  5. We advise you to repeat the treatment. So order two sachets and use one sachet on day 1 (the day you received them) and use the second sachet on day 6.

Fungus Gnats Biological pest control


Have you decided to order these saviours? Super! We do really recommend that you put the Felti into the plant immediately after receiving them. Do you want to keep these saviours for longer? Then keep them in the fridge between 4 °C and 8 °C. The nematodes can be kept for 1 week after receiving them, provided they are cooled. Do not keep the solution in water (in water? this will become clear later on).

Last but not least!

A single application does not guarantee that the mourning flies will disappear forever. In case of an infestation of a larger scale, we recommend you to apply these saviours several times. Wait 1 or 2 weeks each time to really see if your plant(s) are free of these gnats. It is also good to know that these saviours are not big fans of direct sunlight. So make sure that the plant(s) you release these saviours on is/are in a place where the sun never shines too brightly.

PLNTS tip! Use these natural predators in combination with mournin fly catchers, this way you deal with the problem nested in the soil and the little gnats flying around in your urban jungle. Hopefully you will be rid of these annoying creatures quickly!

And that is how you solve your Fungas gnats problem, woohoo! Hopefully this blog was helpful in lending you a helping hand in fighting off your infestation. If you have any additional questions about fungus gnats, or any other pest, you can visit our PLNTSdoctor page. Curious about how to get rid of other pests with biological pest control? Check out this blog, where we link all the blogs with the information you are looking for!


Carlijn is probably one of the biggest plant geeks ever. She is always on the lookout for new gems and loves to share all her plant knowledge, tips and inspiration with our community!

March 18, 2024
Hi, I'm Emma, your guide!

Hi, I’m Emma, your guide!