Fungus Gnats in Houseplants: Break the Life Cycle
Control adults and soil-dwelling larvae by fixing moisture, trapping adults and using targeted biological treatment.
Quick answer: Fungus gnats persist because adults and larvae occupy different places. Let the upper mix dry as the plant allows, improve drainage, trap adults with yellow cards, and use a labelled biological larvicide such as BTI where available. One spray rarely solves the cycle.
Confirm the pest
- Adults are small dark flies that run near soil.
- Larvae live in damp organic mix.
- Check drains and fruit sources so another fly is not blamed.
Reduce breeding conditions
- Extend drying without droughting moisture-loving plants.
- Remove decaying debris.
- Correct oversized pots and blocked drainage.
Treat both stages
- Sticky cards monitor and reduce adults.
- Labelled BTI targets larvae.
- Repeat according to the life cycle and product directions.
Common mistakes to avoid
- Pouring harsh household chemicals into roots
- Replacing soil without changing watering
- Assuming decorative top dressing fixes wetness
What to do next
- Measure your light or inspect the affected plant.
- Check roots, drainage and moisture before buying a treatment.
- Choose one correction and document the result.
Frequently asked questions
Do fungus gnats kill plants?
Heavy larvae can damage vulnerable roots, but adults are mainly a nuisance.
Does cinnamon work?
Evidence is unreliable; moisture correction and targeted control are more dependable.
Should I repot?
Only for failing mix, root damage or a severe infestation that justifies the stress.
Shop with soil fit: Fix the root-zone conditions.
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