How is cinnamon used in orchid culture?
Cinnamon is a natural fungicide. Most people use cinnamon when repotting to prevent rot in roots which are broken or cut.
To use cinnamon, take regular baking cinnamon and lightly dust it over the cut roots which have been wetted. If you don't wet the cut or injured root first, then the cinnamon won't stick. Some people prefer to use peroxide or a little alcohol rather than water.
The imperative word here is "dust", as too much cinnamon can inhibit root growth. Using cinnamon on unaffected roots is probably not a good idea.