How do I deal with fungus gnats after buying new potting soil?

Practical answer

How do I deal with fungus gnats after buying new potting soil?

Fungus gnats are small dark flies that hover around damp potting mix. They are annoying indoors and on sheltered balconies, and they usually appear when fresh organic mix stays wet for too long.

The adult flies are the visible part. The larvae live in moist mix, so the practical fix is to make the top layer less inviting while keeping the plant healthy.

Confirm it is fungus gnats

• Small flies lift from the soil surface when you water or move the pot.
• They stay close to pots rather than flying strongly around the room.
• The problem is worse in constantly damp mix.
• Sticky yellow traps catch small dark flies near the soil line.

Dry the top layer safely

Most established houseplants and many balcony plants can tolerate the upper layer drying between waterings. Seedlings and moisture-loving plants need more care, but even then the surface should not remain wet all the time.

• Water only when the plant needs it, not by calendar.
• Bottom-water suitable pots so the surface stays drier.
• Improve airflow around crowded pots.
• Remove fallen leaves and old organic debris from the surface.
• Check that decorative outer pots are not holding hidden water.

Interrupt the life cycle

• Use yellow sticky traps to reduce adult flies and monitor progress.
• Add a thin dry mineral top layer such as horticultural grit if appropriate for the plant.
• For persistent cases, use a biological control labelled for fungus gnat larvae.
• Repeat monitoring for a few weeks because new adults can emerge after the first improvement.