The influence of harvesting time on the herb crop yield, essential oil (EO) accumulation, its composition and some other characteristics of Origanum vulgare ssp. vulgare (OVV) and ssp. hirtum (OVH) were studied. The crop yield depending on the growing phase varied from 8.0 to 18.1 t ha⁻¹ of fresh herb. The content of EO in OVV was remarkably lower (0.04–0.21 in fresh and 0.20–0.65 cm³ hg⁻¹ in dried herb) than in OVH (0.56–1.86 in fresh and 2.29–5.75 cm³ hg⁻¹ in dried herb). The highest yields were obtained at full flowering stage and slightly reduced after flowering, just before fruiting. The total productivity of OVH oil during different growing phases was remarkably higher (up to 335.9 dm³ ha⁻¹) than that of OVV (up to 37.9 dm³ ha⁻¹). OVV grown in Lithuania belongs to sabinene/β-ocimene/β-caryophyllene/germacrene D chemotype, while OVH belongs to carvacrol chemotype. The fluctuations in the percentage composition of the major compounds in EO throughout harvesting time were rather complex; more consistent changes were observed in the variation of individual constituents expressed in mg per 1 kg of fresh herb. The amounts of pigments, carotenoids and chlorophylls a and b, ascorbic acid, nitrates and soluble solids were measured at different growing phases. Selection of optimal harvesting time is the most important factor for obtaining the highest crop and EO yields from OVV and OVH; flowering phase was proved as the most productive period providing approximately 38 and 336 dm³ ha⁻¹ of the EO, respectively. Determination of optimal harvesting period would increase the grower's ability to control crop yield and EO quality, which is the most important factor in further commercialization of production and application of such products in the preparation of functional ingredients for various industrial uses.