fungus gnats on Calathea
Quick answer
If your Calathea has fungus gnats, the most likely cause is: Fungus gnats (Sciaridae family) exploit the tension between Calathea's need for consistently moist soil and the risk of overwatering. While Calathea requires damp (not soggy) soil, oversaturated conditions in oversized pots or contaminated nursery soil provide ideal breeding grounds. The small black flies lay eggs in the top layer of soil; larvae feed on organic matter and roots, potentially stressing the plant. Calathea's rhizomatous root structure makes it particularly vulnerable when soil remains too wet for extended periods.
Start here:
- 1. Allow top 2 inches of soil to dry between waterings; adjust watering frequency seasonally
- 2. Deploy yellow sticky traps at soil surface to capture adults and monitor population
Why Calathea gets fungus gnats
Goeppertia spp.
Fungus gnats (Sciaridae family) exploit the tension between Calathea's need for consistently moist soil and the risk of overwatering. While Calathea requires damp (not soggy) soil, oversaturated conditions in oversized pots or contaminated nursery soil provide ideal breeding grounds. The small black flies lay eggs in the top layer of soil; larvae feed on organic matter and roots, potentially stressing the plant. Calathea's rhizomatous root structure makes it particularly vulnerable when soil remains too wet for extended periods.
How to reverse fungus gnats on Calathea
- 1
Allow top 2 inches of soil to dry between waterings; adjust watering frequency seasonally
- 2
Deploy yellow sticky traps at soil surface to capture adults and monitor population
- 3
Apply BTi (Bacillus thuringiensis israelensis) drench—Mosquito Bits or similar—as top-dress and water in; safe for ornamentals and kills larvae
- 4
Repot in fresh sterile mix if infestation persists; inspect roots during repot and discard heavily infested soil
- 5
Introduce beneficial nematodes (Steinernema feltiae) as biological control for soil drench
- 6
Consider downsizing pot if oversized—large pots retain moisture too long for Calathea's root system
Keep fungus gnats off this Calathea
Use well-draining soil mix with 30-50% perlite; pasteurize or use pre-sterilized substrates. Apply inorganic top-dressing (gravel, sand, or LECA) to deter egg-laying. Allow top 1-2 inches of soil to dry between waterings. Quarantine new soil bags and plants for 2 weeks. Use self-watering pots with reservoirs only for established, healthy plants.