Damping off
Damping off is caused by soil fungi and water moulds that attack seedlings in cool, wet compost. Seedlings topple over in patches, often with white fluff on the compost, or rot before they even emerge.
Fungal diseases
What it looks like
Seedlings fall like cut grass.
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Collapsed seedlings Seedlings topple in patches. -
Pinched stems Stems thin and brown at the compost surface. -
White fluff Cottony mould on the compost in humid trays. -
Missing seedlings Seed rots before emerging.
How to confirm it
Look at the stem base.
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Thin, dark stem
The stem is pinched and water-soaked at soil level.
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Spreading patches
Collapse spreads outward from a point.
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Wet conditions
Cold, wet, crowded trays.
What to do
Save the rest.
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Remove affected seedlings
Remove collapsed seedlings and the compost around them.
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Let air in
Remove lids and improve ventilation.
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Water from below
Water less, from below, with tap water rather than stored water.
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Resow in clean trays
Start again with fresh compost and clean containers.
Prevent it next time
- Use fresh, sterile compost for sowing.
- Wash trays and pots.
- Sow thinly.
- Keep seedlings warm and light.
What not to do
Do not use water from a water butt for seedlings; it can carry the pathogens.
In the growing guides
Where the guides mention it, with plant-specific advice.
Sources
- Damping off, Royal Horticultural Society