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Have you ever bought a fresh sack of potting soil and discovered a swarm of fungus gnats when you opened it? Unfortunately, this is not uncommon and can hardly be avoided. Because potting soil magically attracts the pests. Mistakes in care can also lead to an infestation in the further course of cultivation. Read here how to avoid them.

Fungus gnats are not uncommon in moist potting soil

No reason to worry

Certainly a plant swarming with fungus gnats is not a pretty sight. The plant itself hardly suffers from an infestation, because

  • only the larvae feed on the leaves.
  • But they grew out after a few days.
  • Flies only eat organic plant debris.
  • Only weakened plants or young shoots are at risk.

As a result, you only have to fight fungus gnats if the infestation is very severe.

recognize fungus gnats

To identify fungus gnats on your plant, you can use one of two methods:

  • Flood the substrate
  • Apply an organic paper strip

flood pot

When there is waterlogging, the fungus gnats fly to the surface. Find out beforehand whether your plant can tolerate the procedure.

Organic paper strip

Since fungus gnats feed on organic plant debris, they will also nibble on the paper strip.

Pay attention to the care of the potting soil

Fungus gnats love moist potting soil. It is therefore better to place your plant on a saucer that you water instead of the substrate. You should always store purchased potting soil in a dry and cool place. Opened bags must be hermetically sealed.


If you simply have no luck buying your potting soil, perlite is a sensible alternative. There is no risk of fungus gnats in the substrate. If you don't want to do without potting soil because hydroponics seems too complex for you, sprinkle some quartz sand on the substrate. This prevents the females from laying eggs.

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