Abstract Thymus hyemalis L. and Spanish T. vulgaris subsp. vulgaris shrubs are characterized by a great chemical intraspecific variability among plants. This fact makes it difficult to detect real changes occurring in their essential oil composition during the vegetative cycle. Because of this, clones of T. hyemalis and T. vulgaris were used to monitor seasonal variations in their aromatic composition of the essential oil. Shrubs were harvested at five different phenological stages during the plant vegetative cycle. Capillary GC/MS with olfactometry analysis was used to determine the volatile profile of the essential oil samples. GC–olfactometry analysis was conducted on each phenological stage for T. hyemalis and T. vulgaris. A total of 96 (T. hyemalis) and 52 (T. vulgaris) aromas were detected with the 27 (T. hyemalis) and 26 (T. vulgaris) most important reported here. The compounds with the most aroma impact for T. hyemalis were linalool, borneol, thymol, and β-damascenone. The compounds with the most aroma impact for T. vulgaris were eucalyptol, borneol, terpinyl acetate, and β-damascenone. β-ionone, myrtenol, and β-damascenone are reported for the first time.