FUNGUS GNATS

Small flies in the soil: solve the moisture problem first

Fungus gnats are common around damp houseplant soil. Adult flies are annoying, but their presence usually tells you that the top layer is staying wet long enough for larvae to develop.

Make sure they are fungus gnats

Fungus gnats are small dark flies that hover around pots and often rise from the soil when you water or move the plant. Fruit flies are more likely to gather around ripe food and drains. If the insects are mainly at the plant and the mix stays damp, fungus gnats are a likely match.

Let the upper soil layer dry

For plants that tolerate it, let the top few centimetres of soil dry before watering again. This interrupts the damp surface conditions larvae need. Do not leave a moisture-sensitive plant bone dry; the aim is a healthier watering rhythm, not drought. Empty saucers and remove decaying leaves from the soil surface.

Use traps as a monitor, not the cure

Yellow sticky traps reduce adult numbers and show whether the population is falling. They do not remove larvae already in the soil, so pair them with better moisture control. If the infestation persists, a biological larvicide formulated for fungus gnats can be useful when used exactly as labelled.

Improve drainage and air in the pot

Compacted soil, an oversized pot and low light all make a pot dry slowly. Check that water can leave through the drainage hole and that the plant is not standing in water inside a cover pot. If soil remains heavy for a week or more, consider repotting into a fresher, more open mix.

Prevent a return

• Water only when the plant’s mix has reached the right dryness level.
• Remove standing water and fallen plant material.
• Use traps early to track adults.
• Give plants the brightest appropriate indirect light.
• Refresh compacted soil when it no longer dries evenly.