Damping off

Updated June 2026

Worst in cold, wet conditions and early spring sowings, August to October.

Damping off is a soil fungus that rots seedlings at the base, toppling them just after they emerge. It strikes in cold, wet, overcrowded seed trays with poor airflow, so clean mix, warmth and careful watering prevent most losses.

How to identify

• Seedlings keeling over with a thin, pinched, rotted stem at soil level
• Whole patches of a tray collapsing within a day or two
• Seeds rotting before they emerge
• A white fungal web over the mix surface in bad cases

How to prevent

• Sow into fresh, sterile seed-raising mix in clean trays
• Avoid overwatering and let the surface dry slightly between waterings
• Give seedlings warmth, light and good airflow, never crowded and damp
• Sow thinly so seedlings are not packed together

How to control organically

• Remove collapsed seedlings and the mix around them straight away
• Hold back on water and improve airflow and warmth
• Water from below and let the surface dry between drinks
• Start again with fresh sterile mix and clean trays if a sowing collapses
• Water with a weak chamomile or seaweed brew, which can help suppress the fungus