White Mold on Homemade Organic Fertilizer: Normal and Beneficial

White mold on a mix of worm castings, guano, and humate is a sign of active fungal decomposition — exactly what you want. These fungi break down raw materials into plant‑available nutrients. The musty smell suggests some anaerobic pockets; ensure good aeration (turn, add coarse material). Do not apply fungicides. Let the mix fully cycle (weeks to months).

Remember: organic "fertilizer" is really a microbial food delivery system. The fungi are your allies.

— The Long Island Gardener