Cinnamon, a common kitchen spice, has gained popularity among organic gardeners seeking natural solutions for plant care. The spice is frequently repurposed as an alternative to synthetic chemicals for everything from encouraging new growth to fighting disease. However, the question of whether cinnamon is harmful to plants does not have a simple yes or no answer. Its effects are highly dependent on how it is used and the concentration applied to the plants. Ultimately, cinnamon possesses powerful biological properties that can be both highly beneficial and significantly damaging.
The Underlying Science of Cinnamon’s Effects
The majority of cinnamon’s impact on plants stems from its high content of an aromatic organic compound called cinnamaldehyde. This compound functions as a natural antimicrobial and fungicide. Cinnamaldehyde works by disrupting fungal cell membranes, which prevents the growth and spread of various molds and mildews that are harmful to plants. The concentration of this active compound varies significantly between the two main types of cinnamon available commercially.
The most common variety, Cassia cinnamon, can contain up to 95% cinnamaldehyde in its essential oil, making it highly potent. In contrast, Ceylon cinnamon, often labeled as “true cinnamon,” typically contains a lower range of 50 to 63% cinnamaldehyde, resulting in a milder effect. This difference in chemical makeup means that Cassia cinnamon carries a greater potential for both effective treatment and accidental harm due to its increased concentration.
Beneficial Uses in Gardening
Gardeners successfully utilize ground cinnamon primarily for its powerful fungicidal and antimicrobial qualities. One recognized application is as a preventive measure against “damping off,” a soil-borne fungal disease that causes new seedlings to suddenly collapse and die. A light dusting of the powder over the soil surface in seed trays creates a hostile environment for the fungal spores. This provides a protective barrier for the vulnerable young stems at the soil line.
Cinnamon is also widely used as a protective aid for propagating plant cuttings. Dipping the cut end of a stem in the powder before planting allows cinnamaldehyde to act as an antiseptic dressing for the open wound. While cinnamon does not contain auxins that stimulate root growth like commercial hormones, its ability to keep the cutting healthy significantly increases the chances of successful rooting.
The strong scent of cinnamon acts as a deterrent for certain soft-bodied pests, such as fungus gnats. When the powder is sprinkled on the growing medium surface, the aroma repels the adult gnats, preventing them from laying eggs in the soil.
Avoiding Toxicity and Plant Damage
Despite its benefits, cinnamon can become harmful to plants when applied incorrectly or at excessive concentrations. The primary risk factor is the natural phytotoxicity of cinnamaldehyde, which is toxic to plant tissue, especially when highly concentrated. Applying pure cinnamon essential oil directly to leaves or stems often leads to chemical burn, resulting in scorched, brown spots on the foliage. Even the powdered form can cause damage if used too heavily on tender young plants or delicate leaves.
A heavy layer of powdered cinnamon on the soil surface can also create a physical barrier, leading to complications with water absorption. When the powder crusts over, it prevents water from penetrating the soil, which can cause the plant to suffer from drought stress. To prevent these harmful outcomes, powdered cinnamon should be applied as a very light dusting, not a thick coating.
When creating a cinnamon solution, a small amount of powder can be steeped in water and then filtered to create a mild antifungal tea. Always use a highly diluted mixture when applying cinnamon to established plants, and test the solution on a small area first to ensure plant sensitivity is not an issue.