Damping Off is a common disease of garden plants in Scotland. Here is what it looks like, the conditions it needs, and the controls that actually work.

A cluster of basil seedlings collapsed at odd angles in a pot, their thin pale stems pinched and browned at soil level while the leaves are still green.
Seedling collapse (basil). Bedlan Gerhard, Dr., Institut fur Pflanzenschutz, BOKU, Tulln, Osterreich, CC BY-SA 4.0
Macro view of several basil seedling stems at soil level, each one thin, water-soaked and browned exactly at the point where it meets the compost.
The diagnostic sign: the stem at soil level. Bedlan Gerhard, Dr., Institut fur Pflanzenschutz, BOKU, Tulln, Osterreich, CC BY-SA 4.0

Controls: what actually works

Every method below is graded by evidence, not by how often it gets repeated. Where a claim has been tested and failed, we say so plainly.

✓Evidence-based

Chemical control

RHS: 'No fungicides are available to gardeners for the control of damping off.'

What actually works: No fungicide exists for this either, so it is won before symptoms show: sow thinly, keep ventilation good, avoid overwatering, and start seedlings in fresh compost and clean pots.

✓Evidence-based

Sow thinly; maintain good ventilation to reduce humidity; avoid overwatering

Sow thinly to prevent crowding, keep ventilation good to reduce humidity, and avoid overwatering.

Ventilation matters here for the same reason it matters for botrytis, powdery mildew, blight and whitefly: airflow is the single most load-bearing practice in Scottish under-cover growing.

✓Evidence-based

Use fresh commercial compost; sterilise or replace pots and trays between uses; use mains water rather than uncovered rainwater

Use commercial growing compost, which is typically pathogen-free; sterilise or replace pots and trays between uses; and use mains water rather than uncovered rainwater.

Timing is half the controlFor diseases driven by wet weather, knowing your season dates is the most practical defence you have.
Frost Date Calculator →

Frequently asked questions

What should I do first if I find damping off in my garden?

Start with sow thinly; maintain good ventilation to reduce humidity; avoid overwatering. After that, use fresh commercial compost; sterilise or replace pots and trays between uses; use mains water rather than uncovered rainwater. The full list of evidenced controls is above, each graded by how much evidence supports it.

Is there a spray that works?

No. There are no amateur fungicides available for damping off. The controls that work are cultural: the measures listed above.

Sources

1 source, recorded with what each was used for
  • RHS1: four causal genera, pre- and post-emergence symptoms, favourable conditions including low light/temperature in spring and unsterile compost, no available fungicides, thin sowing, ventilation, watering, compost and pot hygiene, mains vs rainwater