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Stop Fungus Gnats

Prevention

Gnats showed up after a new plant?

Written by Mustafa Ayan Fact-checked against university extension/IPM sources Last reviewed: October 14, 2026

Direct answer

A new plant is one of the most common ways fungus gnats enter a home, because eggs or larvae can already be in nursery or bagged potting mix. If gnats appeared within a week or two of a new arrival, that plant's mix is the most likely source, not the rest of your collection.

If gnats have already appeared

  1. 1

    Move the new plant away from others

    Adults wander freely between nearby pots. Isolating the likely source slows how fast it spreads while you treat it.

  2. 2

    Set a sticky card in that pot specifically

    This tells you whether the new plant is really the source, or whether an existing plant was already harboring a smaller population.

  3. 3

    Check and adjust the mix's moisture

    Nursery mix is often kept wetter than houseplants need long-term — let it dry appropriately for that plant type before resuming a normal watering routine.

  4. 4

    Follow the standard elimination steps if it's confirmed

    Once you're sure this plant is the source, treat it like any other infestation — traps, moisture control, and a labeled Bti product if needed.

Quarantine, for next time

Keep a new plant away from your existing collection for about a week, with its own sticky card at soil level. If the card stays clean and the soil dries at a normal rate for that plant, it's reasonable to let it join the rest of the shelf. This single habit is one of the more effective, lowest-effort ways to avoid reintroducing an infestation you already cleared, or starting a new one from a fresh source.

The same logic applies to bagged potting soil: if a bag was stored somewhere damp (a garage, a shed, a warm stockroom) before you bought it, treat it with the same suspicion as a new plant rather than assuming sealed packaging means sterile.

Full prevention guide

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