seasonal chenges in essential oil content, yield and composition of spearmint cultivated in shoshtar

spearmint (mentha spicata l.) is one of the most important mint family plants that has numerous applications in food, cosmetical, and pharmaceutical industries due to its valuable medicinal properties. in this research, the change in plant fresh and leaf dry weights, essential oil content, yield and composition during year as randomized complete block design with twelve treatments and three replications was studied. result showed that harvest time had a significant effect on plant fresh and leaf dry weights, essential oil content and yield. the highest plant fresh (1868.7 gr.m-1) and leaf dry (253.3 gr.m-1) weigths were recorded on july and june, respectively. plants also showed highest amount of essential oil content (3.82%) and yield (8.5 gr.m-1) on july. the main essential oil componenens were carvone, limonene, careen, α-pinene, myrecene, β-borbonene, cisdihydrocarvone, dihydrocarveol, dihydrocarvyl acetate, pulgone and trans caryophylene. the highest (67.9%) and lowest (22.4%) amounts of carvone were observed on july and january, respectively. the highest (21.1%) and lowest (4%) amounts of limonene were observed on augest and december, respectively. the maximum amount of caren (5.8%) was obtained on january. cis dihydrocarvone, dihidrocarveol and dihydrocarvyl acetate were increased during winter. in total, spearmint can harvested from may to october but best harvesting time is july.