Preventing Damping Off

Seedling Care

Damping off is the rapid collapse of young seedlings, often at compost level, in conditions that are cold, wet and poorly ventilated. Prevention is far more effective than rescue. Clean equipment, fresh compost, sensible spacing and careful watering create a healthier environment in which seedlings can establish without prolonged stress.

How to do it

Wash seed trays, pots and tools before use, then fill them with fresh peat-free seed compost rather than reused material. Sow thinly, following packet depths and spacing, so air can move around emerging seedlings. Water with clean mains water and let containers drain fully. Keep compost evenly moist, not saturated, and avoid leaving trays standing in water. Give seedlings bright light and good airflow as soon as they emerge; remove propagator lids or coverings gradually once germination is under way. Maintain temperatures suited to the crop, rather than keeping every tray excessively warm. Remove any collapsed seedlings and nearby compost promptly, then improve ventilation and reduce watering if conditions have become humid.

When to do it

Risk is greatest from late winter to spring, when many seeds are raised indoors and light levels can be limited. It can also occur in a crowded greenhouse during damp summer weather. Sow only when you can provide suitable warmth and light, and ventilate regularly whenever temperatures and weather permit.

Tips

Do not overfill trays or pack compost hard, as roots need air as well as moisture. Bottom watering is useful, but empty the base after compost has taken up enough water. Avoid covering seedlings for longer than necessary. If repeated losses occur, review sowing density, drainage, ventilation and light before starting another batch.

Preventing Damping Off: frequently asked questions

How does preventing damping off work?

Wash seed trays, pots and tools before use, then fill them with fresh peat-free seed compost rather than reused material.

When should I do preventing damping off?

Risk is greatest from late winter to spring, when many seeds are raised indoors and light levels can be limited.

What are some tips for preventing damping off?

Do not overfill trays or pack compost hard, as roots need air as well as moisture.

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General guidance for UK gardens. Page updated 18 Sep 2026.