White Mold on Seedling Soil: Damping Off Prevention and Rescue

Fuzzy White Growth on Seed Starting Mix? Act Fast.

White mold/fungus on indoor seedling soil is likely damping off—caused by excess moisture and poor air circulation. It kills young seedlings quickly.

Immediate Rescue Steps

1. Remove any humidity dome/cover immediately.
2. Scrape off visible mold gently.
3. If seedlings have true leaves: transplant into fresh sterile mix, plant slightly deeper.
4. Rinse roots in clean water if heavily contaminated.
5. Water from bottom only; keep moist, not wet.
6. Ensure 12+ hours light, 4–6 inches above plants.

When to Restart

If seedlings are very young (cotyledons only) and mold is widespread, restart in fresh sterile mix. It's faster than nursing weak plants.

Prevention Protocol

• Use sterile soilless mix (vermiculite, perlite, sphagnum)—no garden soil.
• Water from bottom; avoid wet surface.
• Remove dome at first sprout.
• Provide air circulation (small fan on low).
• Don't overcrowd cells.

Key Principle

Damping off thrives in stagnant, wet conditions. Dry surface, moving air, sterile medium = prevention.

Catch it early, transplant to clean mix, adjust environment. Most seedlings recover if they have true leaves.