White Fungus on Bonsai Soil: Calcium Deposits or Mold?

White fuzzy growth on bonsai soil surface. Likely causes:

• Mineral deposits (calcium/lime) from hard water—crusty, not fuzzy.
• Saprophytic fungi/mold—harmless, fuzzy, from organic matter breakdown.
• Mealybugs/root aphids—cottony, on roots/stems.

Action

1. Scrape off surface layer; top-dress with fresh soil.
2. Switch to rain/distilled water if deposits.
3. Improve air circulation.
4. If pests suspected, treat with neem oil or insecticidal soap.

Diagnosis

Post photo on Learning2Bonsai for ID.