The plants were cultivated in the Botanical Garden of the University of Agriculture, Plovdiv/Bulgaria on meadow-carbonate soil with neutral reaction (pH 7.1-7.2) and were harvested during the flowering period (July and September). The reserves of nitrogen, phosphorus and potassium in the soil (NPK) were: NH⁴⁺ 31.42 mg/kg; NO^3- 16.66 mg/kg; P₂O₅ 12.3 mg/100 g and K₂O 11.4 mg/100 g. Ammonium nitrogen and nitrate nitrogen were extracted from the soil with a 1% solution of KCI and were determined by consecutive distillation on a Parnas-Vagner apparatus. Phosphorus was determined by the Egner-Ream method and potassium was extracted with 2 n HCI and was determined by flame photometry. The plants were grown as seedlings and were planted in a two-row bed 50 × (20 + 20) cm in patches of 5 m². A scheme on the increase was used for the introduction of N, P and K fertilizers. The experiment was carried out as a randomized block modus - 15 variants in 4 replications (6 levels for N and 4 levels for P and K). Phosphorus (triple superphosphate - 50 % active substance) and potassium (potassium sulphate - 50 % active substance) were introduced only once before planting. Nitrogen (the ammonium nitrate - 33 % active substance) was introduced in three portions - during preparing of the soil, during the plants drafting (active vegetation) and at the full bloom.

The highest oil yield was obtained from leaves in July for N4P2K4 (0.63%) and the basic components were piperitenone (29.4%) and piperitone (13.5%). The mineral fertilization had no effect on the oil yield from the flowers. Regardless of the variant, it was found that the flower oils in July were rich in caryophyllene oxide (12.0-48.4%) and piperitenone (3.0-7.0%), while the oil composition in September was different.