Damping Off

• Seedlings collapse at the soil line, stem pinched or rotted just above the root
• Seeds fail to emerge despite adequate conditions
• Emerged seedlings suddenly fall over and die, often in groups
• Stem base appears water-soaked, then brown and shriveled
• White mold may be visible on the growing medium surface in severe cases

Damping off is caused by several soil-borne pathogens that attack seedlings when conditions favor them: cool temperatures, overwatering, poor drainage, and high humidity. Pythium thrives in cold, wet conditions; Rhizoctonia prefers warmer, wet soil. The pathogens are common in unsterilized garden soil and can arrive on dirty tools, recycled containers, or contaminated water.

1. 01Use fresh, sterile seed-starting mix — never garden soil or reused mix from previous seasons
2. 02Sow seeds at the recommended depth and avoid overwatering — let the surface dry slightly between waterings
3. 03Provide good airflow and light to seedlings; a small fan on low setting reduces surface moisture
4. 04Water from the bottom (set tray in water) to avoid wetting seedling stems
5. 05Provide warmth for germination — cold soil slows emergence and prolongs exposure to pathogens
6. 06Disinfect containers with a 10% bleach solution before reuse
7. 07Thin seedlings to recommended spacing to improve airflow

If damping off recurs even when using fresh sterile mix and following good practices, an extension plant pathologist can help identify the specific pathogen and advise on biological seed treatments (like Bacillus subtilis products) that may suppress the problem.

• Damping Off of Seedlings— University of Maryland Extension
• Damping Off— Ohio State University Extension