Seasonal and Diurnal Variations in the Yield and Chemical Composition of Lippia grata Schauer Essential Oil

Lippia grata Schauer is an aromatic species native to the Brazilian Caatinga, widely recognized for its medicinal potential due to the presence of carvacrol and thymol in its essential oil (EO). Environmental factors such as seasonality and harvest time can strongly influence biomass production and EO chemical composition. This study evaluated the effects of three seasons (summer, winter, and spring) and two harvest time (morning and afternoon) on plant biomass, EO yield, and chemical profile of L. grata cultivated in the Brazilian semiarid region. EOs were extracted by hydrodistillation and analyzed by GC–MS. Season significantly affected fresh and dry biomass, EO yield, and the contents of carvacrol and thymol. The highest EO yield was observed in spring (4.92%), whereas summer promoted greater fresh biomass (255.0 g) and higher concentrations of carvacrol (59.28%) and thymol (6.99%). Harvest time influenced carvacrol content, with higher values recorded in the afternoon (58.35%). The interaction between season and harvest time significantly affected p-cymene content. These results demonstrate that both seasonal and diurnal variations are key factors regulating the quantity and quality of L. grata EO, providing important information for optimizing harvest strategies for medicinal and industrial purposes.