Damping Off

Symptoms by part

Causes

• Overly wet or waterlogged soil conditions.
• Poor air circulation around the seedling trays.
• Using non sterile or reused potting soil.
• Overcrowding seedlings which traps moisture.
• Cool, damp temperatures that slow seedling growth while favoring fungal activity.

Could be confused with

• Fungus gnats · Gnat larvae eat roots but do not cause the characteristic water soaked constriction at the stem base.
• Heat stress · Seedlings wilt from lack of water but the stems remain firm and green rather than turning mushy or brown.

Treatment

1. Remove all infected seedlings and the surrounding soil immediately to prevent the fungus from spreading to healthy neighbors.
2. Increase airflow around the remaining seedlings by using a small fan or spacing the containers further apart.
3. Reduce watering frequency to allow the top layer of soil to dry out slightly between waterings.
4. Repot any remaining healthy seedlings into fresh, sterile seed starting mix.

Without chemicals

• Use only new, sterile seed starting mix for every batch of seeds.
• Ensure all seed trays and pots are thoroughly cleaned and disinfected before use.
• Provide bright, indirect light to encourage strong, fast growth.
• Bottom water the seedlings to keep the surface of the soil dry.

Preventing it

• Always use fresh, sterile potting medium instead of garden soil.
• Disinfect all trays, pots, and tools with a mild bleach solution before planting.
• Avoid sowing seeds too densely to ensure good airflow.
• Keep the growing area warm and well ventilated.
• Use a fan to keep air moving across the surface of the soil.

When to act

Act the moment you see a seedling topple or notice a dark, thin spot on a stem. Since damping off kills quickly, remove affected plants immediately to save the rest of your tray.

Questions people ask

Can I save a seedling that has already fallen over?

Unfortunately, no. Once the stem has constricted and the plant has collapsed, the vascular system is destroyed and the seedling cannot recover.

Is it safe to reuse the soil from a tray that had damping off?

No, the soil will be contaminated with fungal spores. It is best to discard that soil or use it for non seedling garden beds away from your starts.

Why does my soil grow white fuzz on top?

That is often just harmless surface mold from damp conditions, which is different from the pathogens that cause damping off. However, it is a sign that your soil is staying too wet.

Plants it affects

• Dill
• Red Amaranth