Disease
Damping off
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in February | Watch for in March | Watch for in April | Watch for in May | Watch for in June |
What it is
Damping off is not one disease but a collection of soil and water moulds and fungi that attack seedlings and germinating seeds. It is the commonest reason trays of spring sowings fail on windowsills and in greenhouses, and it can wipe out a pot of basil or lettuce seedlings almost overnight.
Symptoms
Seedlings develop a pinched, brown, water-soaked area at the base of the stem, then flop over and shrivel, often in patches that spread outwards across the tray. A fine white or grey cobweb of mould may cover the compost surface. Sometimes seeds rot before they emerge at all, which can be mistaken for poor germination. Leggy, pale seedlings that lean but stay firm are simply short of light, not diseased.
Cause
The organisms live in soil, old compost, dirty pots and stored rainwater. They thrive in cold, wet, airless conditions, so overwatered compost, thick sowing, low light and stagnant air give them the upper hand. Seedlings are most vulnerable in their first couple of weeks, before the stems toughen up.
Control
Once a seedling has collapsed it will not recover. Remove affected seedlings and the compost around them at once, and if much of the tray is hit, start again with fresh materials. Prick out any healthy survivors into clean compost and water them sparingly. There are no garden fungicides worth using against damping off; prevention is far more effective.
Prevention
Sow into fresh seed compost and wash trays and pots in hot soapy water first. Sow thinly and cover lightly, then water from below with tap water rather than water from a butt. Keep compost moist but never soggy, give seedlings bright light, and open vents or crack a window to keep air moving. Wait until soil warms before sowing outdoors.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: February, March, April, May and June.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.