If you are going to use a spice to treat damping-off, cinnamon is your best choice. It probably works to some extent, but there is no direct scientific evidence that it will prevent damping-off in seedlings.

How can damping off be prevented?

Damping off can be reduced by planting fungicide-treated seed directly into the garden. Other preventative measures include using well-drained soil and avoiding overcrowding of plants. Also, clean out all pots thoroughly before reuse and discard contaminated soil.

How do you use cinnamon for damping off?

I sprinkled cinnamon on the infected seedlings as a way to kill off the fungi or 'damping off' disease and stop its potential spread. You could also lightly sprinkle your starting mix with cinnamon right after the seeds are planted.