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Home Remedies.
I doubt that a cinnamon stick in the potting medium would dry out the roots, or do any preventive good.
Root desiccation is as a result of the powder in contact with it, not the active ingredient, as far as I can tell. Spraying the roots with a cinnamaldehyde infusion does not cause desiccation for me.
However, in raw bark form, the surface area is so low, very little with diffuse into the medium to do any good.
Then there is that "trumping" factor: if you're getting fungus or rots in your potting medium, then it's your culture that needs improvement, not the application of a "magic potion".