What Is Damping Off?
Damping off is a common seedling problem in which young plants suddenly topple and collapse at soil level. It is caused by several soil-borne fungal problems that thrive in cold, wet, poorly ventilated conditions. It can be disappointing, but careful hygiene and gentler watering greatly reduce the chance of it returning.
Confirm the problem before changing your routine. Seedlings affected by damping off often look healthy one day, then develop a thin, darkened or pinched stem at compost level and fall over. They may rot rather than simply wilt. This differs from ordinary thirst, where the stem remains firm and plants usually recover after watering. Remove collapsed seedlings promptly, along with a small area of surrounding compost, so spores are not splashed onto neighbours. Do not try to pot on weakened survivors. Empty heavily affected trays into green waste rather than saving the compost for seedlings. Wash your hands after handling them, then inspect nearby trays daily for further losses.
Begin the next sowing with clean equipment. Brush old compost from module trays, pots, labels and propagator lids, then wash them thoroughly in hot water and allow them to dry. Use fresh peat-free seed compost, which has a finer texture and is less likely to contain troublesome debris than old potting material. Do not reuse compost from a failed tray for seed sowing. Fill modules loosely, tap them to settle, and sow according to the packet depth rather than burying tiny seed too deeply. Cover only where required, using a thin layer of compost or vermiculite. Label and date each tray, which makes it easier to spot slow germination before conditions deteriorate.
Water with restraint from the moment you sow. Aim for compost that feels evenly damp, not saturated and shiny. If the compost is dry when filling trays, moisten it before sowing so seeds are not displaced by a heavy watering afterwards. Use mains water for indoor sowings rather than water from a water butt, which can carry organisms and debris. Water from below where practical by standing modules briefly in a shallow tray, then remove them and let excess drain away. Do not leave pots sitting in water. Check moisture with a fingertip every day, especially beneath a propagator lid, and only add water when the surface is beginning to dry.
Give seedlings warmth appropriate to the crop and plenty of moving air. Cold, stagnant compost is an ideal setting for damping off. Position trays in a bright place, but avoid a cold windowsill at night or fierce midday sun under a clear cover. Once most seeds have germinated, remove propagator lids or open vents daily. In a greenhouse or polytunnel, open doors or vents when conditions allow, while protecting tender plants from sharp cold. Space trays so air can circulate around them rather than packing them tightly together. If seedlings are crowded in one module, snip out the weakest with clean scissors rather than pulling them and disturbing neighbouring roots.
Sow thinly so each seedling has light and airflow. Overcrowding keeps foliage wet, shades the compost and makes it harder for stems to dry after watering. For very fine seed, mix it with a little dry horticultural sand before sowing, or use a folded piece of paper to guide a sparse sprinkle. Prick out seedlings when they have their first true leaves, holding them by a leaf and easing roots apart with a label. Pot them into fresh peat-free multipurpose compost and water lightly. Do not feed newly germinated seedlings unless the compost and crop require it. Strong, stocky growth is safer than soft, rushed growth.
If damping off keeps happening, alter one condition at a time and keep notes. Move sowings to a warmer, brighter position, reduce watering frequency or use smaller modules that do not remain wet for long. Avoid sowing tender vegetables too early in an unheated greenhouse, particularly in cooler northern gardens and Scotland. In the milder south, ventilation may be the priority on sunny spring days. Start again with fresh compost and cleaned trays rather than trying to salvage a widespread outbreak. Some losses can still occur, especially in dull wet weather, but a clean, airy setup with moderate moisture normally gives seedlings a much better start.
Frequently asked questions
Can seedlings recover from damping off?
A seedling with a pinched, dark stem at compost level rarely recovers because its water-carrying tissues have been damaged. Remove it promptly. Nearby seedlings that are still upright may survive if you improve airflow, stop overwatering and allow the compost surface to dry slightly. Avoid moving or feeding them until they are growing strongly again.
Is damping off caused by poor-quality seed?
Usually not. The problem is mainly linked to organisms in wet compost and conditions that favour them, especially low temperatures and stale air. Old or weak seed can germinate slowly and remain vulnerable for longer, so use seed stored properly and within its useful life, but concentrate on tray hygiene and growing conditions.
Should I use rainwater for seedlings?
For indoor seed sowing, mains water is the safer choice because stored rainwater can contain organic material and microorganisms. Rainwater from a water butt remains excellent for established garden plants. If you use it for seedlings, keep the butt clean and water sparingly, but changing to mains water is sensible after a damping-off outbreak.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 19 Sep 2026.