Gardeningknowhow.com had an article that claimed cinnamon could be used to deter ants in a house or greenhouse because “ants don’t like to walk where cinnamon powder is…” Another claim is that cinnamon works as a rooting compound, stimulating root growth. Additionally, cinnamon can be used as a fungicide to alleviate disease. It is also believed to prevent fungus growth in planters, compost or mulch.
Years ago I read research reporting that ants could be killed with talc. The ants would get the powder all over them walking through it and carrying it back to their nest. The powder prevented them from absorbing water through their exoskeleton, causing the ants to dry out and die. Maybe the effect is the same with cinnamon.
Morningchores.com claims that cinnamon discourages the fungal disease known as rust, when sprinkled on the soil when planting. In addition, this cinnamon can “heal plant wounds”. It is supposed to repel rabbits, mice and rodents by confusing their “olfactory instincts”. The author writes that it “keeps mosquitoes out”. She states that it can also be used effectively on houseplants, although I would worry about it burning the leaves. She reports that there is no scientific evidence to back up claims that cinnamon is beneficial to plants, just anecdotal evidence, but that cinnamon can’t harm anything either, which isn’t necessarily true. .
Plants do not have the ability to “heal” wounds. If trimmed correctly, they compartmentalize the injured area, closing it off. It’s not healing. I’m willing to try cinnamon in ground squirrel holes under the house. The smell would be much better than mothballs! I wonder if that would deter cats from using flower beds as a litter box. I don’t know how putting cinnamon on the floor prevents mosquitoes.
There is research to back up some of the claims about cinnamon, primarily its oils. The National Library of Medicine in an article (Kowalska, J. et al. August 31, 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433798/) reviewing research on cinnamon, states that “due to its antibacterial and pharmacological properties, it can be used in processing, medicine and agriculture. Researchers reported that “cinnamon acts on parasites primarily as a repellent, although at higher doses it has a biocidal effect and prevents egg laying”. Cinnamon oils and extracts “impede bacterial and fungal growth…” Because they can, in certain cases and quantities, also damage plants, it may be a possible herbicide. “It can be used in organic farming as a promising alternative to chemical pesticides for use in plant protection…”
If you decide to try cinnamon powder, to avoid burning the plants, it may be best to apply it only to the soil, not directly to the leaves. You must beware. Do not inhale cinnamon, as it can burn your nasal and lung passages.
JoAnne Skelly is an Associate Professor and Distinguished Extension Educator at the University of Nevada Cooperative Extension. Email firstname.lastname@example.org