Damping off is caused by fungal pathogens present within the soil which cause seedlings to collapse and die. It can also occur in the seed as pre-emergent damping off. It can affect all plant types and once a plant is infected it cannot be treated. However, putting preventative measures in place can stop it from occurring.

Damping off occurs most commonly in cool, damp conditions, and it effects very young seedlings. It can be more prevalent in spring when light and temperature levels are low, leading to slow seedling growth. There is a period of susceptibility for young plants which passes as the plant grows older. Growing plants in warmer conditions with good ventilation will encourage healthy plant growth and see the seedling through the vulnerable stage into safety.

Much of the advice online advocates for sterile growing conditions, using bleached or new pots, sterile growing mediums and treated tap water. I would like to counter this advise by suggesting that growing seedlings in ‘living soil’ that is full of beneficial organisms will keep pathogenic fungi at bay. Providing that your living biological amendments (inoculation grade compost, home-made compost or worm castings) contain plenty of beneficial organisms, pathogens should be kept at bay, all while accelerating plant growth through plant-microorganism symbiotic relationships.

Whether you decide to go down the ‘sterile’ or ‘beneficial biology’ route, there are other measures that can be followed to prevent damping off. Sowing seed too thickly can increase humidity around the plants which encourages fungal pathogen reproduction. Sow seeds thinly to allow more space between them. Do not overwater your seed trays, this again will provide the perfect conditions for pathogenic fungal growth. Adding grit or perlite to your potting mix might help to reduce overly wet composts. If you are using a humidity dome or covering your seedlings, remove them for a period each day to ventilate the seed trays. It may also help to ventilate greenhouses during the day for extra fresh-air flow.