Changes in Growth and Chemical Composition of the Essential Oil from Flowers and Leafy Stems of Lavandula angustifolia Grown in Media Amended with Bark and Sewage Sludge

The growing medium is one of the key factors determining the yield and quality of lavender oil. The research conducted in greenhouse conditions aimed to assess the impact of a substrate with a reduced peat content enriched with compost from sewage sludge and bark on the growth, yield, and chemical composition of the oil from the inflorescences and leafy stems of English lavender 'Sentivia Blue'. The plants were grown in pots filled with peat and chemical fertilizer, or in a substrate containing bark and sewage sludge compost, with or without fertilizer. Media affected the growth, leaf greenness index, and biomass production of lavender. Plants growing in peat with fertilizer were the tallest and widest. In turn, the highest number of inflorescences and the highest dry weight of inflorescences and leafy stems were found in plants grown in a mixture of bark and sewage sludge compost, with the addition of fertilizer. A significant interaction between the plant organ and the type of substrate was demonstrated, which affected the content of specific oil components. The content of essential oil was higher in inflorescences (1.15%) than in leaves (0.21%). The oil from the inflorescences was dominated by linalool, caryophyllene oxide, and linalyl acetate, while caryophyllene oxide, borneol, and geranyl acetate dominated in the leafy stems. The highest linalool content was found in oil obtained from inflorescences of plants grown in both media, based on bark and sewage sludge compost. The results show that the best quality parameters of the raw material and oil, including particularly high dry weight and linalool content, were obtained when the plants were grown in a medium consisting of bark, sewage sludge compost, and chemical fertilizer.