✍️ Sonia Pardasani, Co-founder BageechaBox | 🕐 6 min read | 🛡️ Troubleshooting Guide
Quick answer: First do the spray test — mist the fuzzy patch with water. If it collapses flat, it's harmless root hairs. If it stays fluffy or looks slimy, it's fungus. Stop top watering immediately, increase airflow, and treat with a light dusting of cinnamon powder or a diluted hydrogen peroxide spray. Discard the tray if fungus covers over 30% of the surface.
You open your tray and see white fuzzy patches spreading across the surface. Don't panic — fungus is one of the most common problems in microgreens growing, and if caught early, you can often save the tray. Here's exactly what to do.
First — Is It Root Hairs or Fungus?
Before doing anything, do the spray test: mist the fuzzy area with water.
- Root hairs: Fine, uniform white threads radiating from the base of the stem. They collapse flat against the root when sprayed. No smell. Completely normal and healthy. ✅
- Fungus: Cottony or fluffy patches that stay fluffy or look slimy after spraying. Often has a musty or sour smell. Spreads visibly over 24–48 hours. ❌
If it stays fuzzy after the spray, it's fungus. Act immediately.
Why Does Fungus Appear?
- Overwatering — wet cocopeat surface is the #1 cause.
- Poor airflow — stagnant air allows spore concentration to build.
- High seed density — too many seeds prevents air from reaching the medium surface.
- Dirty trays — reusing trays without sterilisation carries spores from previous batches.
5-Step Rescue Plan
Step 1 — Stop Top Watering
Switch to bottom watering only. This keeps the canopy and surface dry.
Step 2 — Increase Airflow
Position a fan to circulate air gently around the tray. In humid cities, keep it running 24 hours.
Step 3 — Apply Cinnamon Powder
Sprinkle a light dusting of cinnamon (dalchini) directly over the affected area. Natural antifungal. Don't overdo it.
Step 4 — Hydrogen Peroxide Spray (Moderate Cases)
Mix 1 tablespoon 3% hydrogen peroxide in 1 cup water. Spray lightly on affected area. Safe for plants, lethal for fungal spores.
Step 5 — Know When to Discard
If fungus covers more than 30% of the surface, smells strongly, or spreads to stems — discard the tray. Start fresh with clean trays and sterilised cocopeat.
Frequently Asked Questions
How do I tell the difference between root hairs and fungus?
Mist the fuzzy area with water. Root hairs are fine, uniform white threads that collapse flat against the root when sprayed and have no smell — they're completely normal. Fungus stays cottony or fluffy after spraying, often smells musty or sour, and visibly spreads over 24–48 hours.
What causes fungus on microgreens?
The four main causes are overwatering (a wet cocopeat surface is the #1 cause), poor airflow letting spores concentrate, high seed density blocking air from reaching the medium surface, and dirty trays that carry spores from previous batches.
Does cinnamon powder stop fungus on microgreens?
Yes, cinnamon (dalchini) is a natural antifungal. Sprinkle a light dusting directly over the affected area — don't overdo it. It's most effective when combined with stopping top watering and increasing airflow.
Is hydrogen peroxide safe to spray on microgreens?
Yes, in the right dilution. Mix 1 tablespoon of 3% hydrogen peroxide in 1 cup of water and spray lightly on the affected area. It's safe for the plants but lethal for fungal spores — reserve it for moderate cases.
When should I throw away a moldy microgreens tray?
Discard the tray if fungus covers more than 30% of the surface, smells strongly, or has spread to the stems. Start fresh with clean, sterilised trays and cocopeat rather than trying to salvage a heavily affected batch.
🌱 Starting fresh after fungus? High-germination seeds and professional trays reduce reinfection risk.
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