How do I get rid of fungus gnats in plant soil?

Let the soil dry out completely between waterings, apply BTi (Bacillus thuringiensis israelensis), and set yellow sticky traps to catch adults.

Why do fungus gnats appear in my plant?

Fungus gnats are attracted to constantly moist soil. Overwatering or a pot without drainage holes creates the perfect breeding environment.

Are fungus gnats dangerous for plants?

Adult flies are harmless, but their larvae can chew fine roots. A severe untreated infestation can cause progressive plant decline.

How long does it take to eliminate fungus gnats?

With proper treatment (reduced watering + BTi + sticky traps), the infestation reduces in 2–4 weeks.

Can I use natural products against plant gnats?

Yes. Silica sand on the soil surface prevents females from laying eggs. BTi is effective and safe for plants and pets.

Verdier

Diagnostic Botanique · IA

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Apr 20264 min read🇬🇧 EN

Fungus Gnats in Plant Soil — Causes and Solutions

Tiny black flies hovering around your houseplants? Those are fungus gnats. Here is how to identify them, understand why they appeared, and eliminate them completely.

What are fungus gnats?

Fungus gnats (Sciaridae) are tiny dark flies, 2–3mm long. Adults are harmless — but their larvae feed on plant roots, weakening the plant.

Why do they appear?

Attracted to constantly moist soil. Main cause: overwatering. Pots without drainage make it worse.

4-step elimination protocol

Step 1: Dry out the soil

Stop watering entirely. Larvae cannot survive without moisture.

Step 2: Set sticky traps

Place yellow sticky traps near the pot to catch adults.

Step 3: Treat with BTi

Water with Bacillus thuringiensis israelensis (BTi) solution to kill larvae in the soil.

Step 4: Cover the soil

Apply silica sand or fine gravel — prevents females from laying eggs.

With proper treatment, infestation reduces in 2–4 weeks.

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