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# Damping off and seedling mould

You check on your seedlings and find them toppled over at soil level, their stems pinched and thin — or a film of white, fuzzy mould on the compost. This is damping off: a fungal problem that thrives in cold, wet, still air. A collapsed seedling cannot be saved, but you can stop it spreading.

## How to recognise it

| Sign | What it looks like |
| ---- | ---- |
| Collapsed | toppled at the base |
| Pinched stem | thin and dark at the soil line |
| White mould | fuzzy film on the compost |
| Sudden wilt | healthy in the evening, floored by morning |

## What causes it

- **Too much water.** Wet, airless compost is the perfect home for the fungi involved.
- **Poor airflow.** Still, humid air under a lid that never comes off.
- **Overcrowding.** Densely sown seedlings trap moisture and shade each other.
- **Cold compost.** Slow-growing seedlings in cold, damp mix are far more vulnerable.
- **Dirty pots or reused compost.** Old trays and used compost can harbour the fungi.

## What to do now

- Remove affected seedlings and the compost around them straight away.
- Take any covers off and add a gentle fan.
- Let the surface dry out a little: stop misting and water sparingly, from below.
- Move the tray somewhere brighter and a touch warmer.
- If a whole tray is lost, start again with clean pots and fresh compost. With fast crops you lose little time.

## How to prevent it

| What | How |
| ---- | ---- |
| Clean pots | wash before use |
| Fresh compost | seed-grade |
| Sow thinly | space to breathe |
| Water from below | keeps the surface drier |
| Good airflow | vent the lid |
| Warm and bright | steady growth |

It comes down to clean, warm, airy and not too wet. Take covers off as soon as the seeds germinate. Strong, fast-growing seedlings rarely succumb.

## Frequently asked questions

**Can I save a seedling that has collapsed?** No. Once the stem has gone, that seedling is lost. Focus on protecting the rest.

**Is the white mould harmful to me?** It is a seedling problem, not a hazard to you. More airflow and less water clear it.

**Can I use tap water?** Yes. How much you water and how much air there is matter far more than the water itself.

**Does it affect grown plants?** Damping off mainly strikes young seedlings. Established plants are far more resistant.

The full version of this guide is on [seedschoice.com](https://seedschoice.com/blogs/news/damping-off-seedling-mould).
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