This paper presents the results of a study conducted over the period 2016–2017 which was designed to determine to what extent crop irrigation and raw material drying process determine the content and composition of lavender essential oil. In cultivation with irrigation, a higher yield of fresh and yield of air-dried inflorescences was obtained compared to cultivation without irrigation. The use of supplementary irrigation in lavender crops contributed to an increased amount of essential oil (EO) compared to plants without irrigation. The main components of the essential oil were linalyl acetate, linalool, and E-caryophyllene. In EO obtained from plants cultivated with irrigation, the share of oxygenated monoterpenes (OM) was higher and the share of hydrogenated monoterpenes (HM) was lower than in the oil from plants without irrigation. The EO content in lavender flowers dried at a temperature of 30°C was twice higher than in those dried in natural conditions. In 2016 in which the air temperatures were high and a greater number of sunshine hours was recorded in July and August, plants accumulated more EO than in 2017. Study shows that there are prospects for practical application of crop irrigation in lavender cultivation and of raw material preservation method in order to modify EO content and chemical composition.