Substrates in Organic Mint Cultivation: Growth, Phytochemistry and Biological Activities

Mentha piperita is an essential oil (EO)-producing species with high commercial relevance. Its EOs are widely used in the pharmaceutical, fragrance, food and cosmetic industries. This study evaluated alternative substrates to industrial fertilizers, aiming to enhance plant development and EO yield while reducing environmental impact and costs. Three treatments were tested: corrected soil (CS), soil with vermiculite, vermicompost, and rock powder (SVR), and soil with bovine manure (SM). Growth parameters, macro- and micronutrient content, antioxidant and enzymatic activity (PAL), EO yield, and chemical composition were assessed. The SM treatment resulted in the highest fresh and dry biomass, nitrogen content, and PAL. The SVR treatment showed higher potassium levels, shoot/root ratio, and arylsulfatase activity. EO yield was similar across treatments, but SM had the highest carvone content (74.18%). Anthocyanin concentration was higher in SM, whereas antioxidant activity, assessed by DPPH and β-carotene assays, was greater in CS (3.98% and 96.25%, respectively) and SVR (2.96% and 98.59%, respectively). CS also exhibited higher phenolic content (687.65 mg GAE 100 g−1). Overall, CS and SVR enhanced antioxidant potential; however, considering biomass productivity, the use of bovine manure (SM) demonstrated greater potential, making it a more advantageous and sustainable alternative for M. piperita cultivation compared to the other treatments.