Damping Off: Why Seedlings Keel Over and How to Stop It

Damping off is one of the most discouraging seedling problems because it appears suddenly and spreads fast. A tray of seedlings looks healthy one day and has a section of collapsed, wilted stems the next. The affected seedlings don't recover -- the stem tissue at or below the soil line has been.

Damping off is one of the most discouraging seedling problems because it appears suddenly and spreads fast. A tray of seedlings looks healthy one day and has a section of collapsed, wilted stems the next. The affected seedlings don't recover — the stem tissue at or below the soil line has been killed, and the plant above it dies within hours to days.

The cause is a complex of fungal and oomycete pathogens that thrive in specific conditions. Understanding those conditions — and why they occur in indoor seed-starting situations — allows reliable prevention.

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What Damping Off Looks Like

Per Penn State Extension, damping off appears in two forms:

Pre-emergence damping off: Seeds germinate but the seedling rots before breaking the soil surface. The tray shows germination gaps with no apparent cause. Seeds may have sprouted but died underground.

Post-emergence damping off: Seedlings emerge normally but then wilt and collapse. The stem appears pinched, water-soaked, or discolored at or just below the soil line. The seedling falls over; the roots may be intact or partially rotted.

In both forms, the damage is at or near the soil line. The seedling above the lesion is often still green at the time of collapse.

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