Damping off is the bane of those who start their own seed. One day seedlings will be growing in sturdy profusion and the next the stems will turn watery at the soil line and fall over. Despite the fact that the top of the plants look fine they will rarely recover. It is doubtful if there is a cure once damping off hits a seedling.
There are methods to prevent damping off, which is a fungus disease caused by a mixed batch of fungi. There are two types. Pre-emergent damping off occurs when the seed swells or when the radicle begins to extend from the seed. These seeds will not complete germination. Post emergent damping off is manifested by the seedlings falling over.
Cleanliness is important in evading this disease and preventing any spores present from multiplying. Since seeds can be contaminated, using a sterile potting mix will not guarantee freedom from the fungus. Wash pots a 10% bleach solution.Seeds may also be soaked in a 5 % bleach solution or in a solution of 2 tablespoons of 3% hydrogen peroxide to two cups of water. The seeds need only be soaked for 10 minutes or so. It might be a good idea to use this on newly bought tomato seeds this year, as there is the possibility that last years seeds might be contaminated with the late tomato blight.
Air movement between the seedlings is important. If you are plagued with this problem, try setting up a fan in your germination area. Don’t aim the fan directly at the plants but make sure it keeps the air circulating in the room. Consider planting the seeds with a bit more space between them to improve air circulation.
Spritzing seedlings with chamomile tea can also be helpful as a preventative. Again, a solution of hydrogen peroxide can be used in this way. The suggested concentration is 1 cup of 3% hydrogen peroxide to 1 gallon of water. Cinnamon, cloves or powdered charcoal sprinkled on the soil is also a deterrent.
DON’T OVERWATER! That is probably the most important factor. Also stressed plants that aren’t getting enough light or are kept too cold are more susceptible. If you spot an infected tray remove it immediately as this disease spreads rapidly.