Essential oils of Portuguese Thymus mastichina (L.) L. subsp mastichina grown on different substrates and harvested on different dates

The effects of harvesting date and different substrates on the yield and chemical composition of the essential oils of Portuguese Thymus mastichina (L.) L. subsp. mastichina were compared with samples grown in pots. The best oil yields were obtained in June (3.2, 3.6 and 4.9% in the local sandy soil, in non-fertilized peat, and in fertilized peat, respectively). The essential oils were dominated by 1,8-cineole, the highest concentration of which was detected in June (58.6%) in samples kept in non-fertilized peat, and the lowest values were from plants growing in fertilized peat during April and June (45.1%). The remaining samples always reached the highest percentages in October (around 54% in both oil samples), although the concentration profile over time was similar in every sample. Concerning the monoterpene hydrocarbons, a-pinene, camphene, sabinene and P-pinene were the most significant components. While the amounts of alpha-pinene tended to decrease from April to June, for P-pinene such tendency was observed from October to January, independently of the growing material used. Amounts of camphene, being similar to those of alpha-pinene, decreased successively from October to April. Elemol and intermedeol were the most representative sesquiterpene components, although the concentrations never exceeded 2.2% and 1.3%, respectively. The results obtained in this work suggest that the harvesting dates of Portuguese T mastichina influence oil yields and their chemical compositions much more than the different growing media used, although a higher oil yield was obtained with the fertilized growing material