Hyssop (Hyssopus officinalis L.) is a perennial plant of Mediterranean origin. The raw material is the herb (Hyssopi herba) that shows multidirectional medicinal activity. Essential oil is the main biologically active substance. The content of oil and its chemical composition determine the aroma of the raw material. The essential oil content changes during the period of plant growth. The aim of this study was to evaluate the qualitative and quantitative composition of hyssop oil depending on plant growth stage. Studies were conducted in the period 2007–2008 at the Experimental Farm of the Department of Vegetable Crops and Medicinal Plants, University of Life Sciences in Lublin. The hyssop herb was collected from plants at the following growth stages: vegetative stage (the middle of June), beginning of flowering (the middle of July), and full flowering (the middle of August). The herb was dried at a temperature of 30^oC and then ground through 4–5 mm mesh sieves. Essential oil was obtained from the ground herb by steam distillation. The main components of hyssop oil were as follows: cis-pinocamphone, trans-pinocamphone (monoterpene ketones), β-pinene (monoterpene hydrocarbon), germacrene D (sesquiterpene hydrocarbon), and elemol (sesquiterpene alcohol). Trans-pinocamphone was predominant in the oil extracted from hyssop collected at the vegetative stage, but its content decreased with plant growth, while the content of cis-pinocamphone increased. The content of β-pinene was the highest in the oil extracted from hyssop cut at the vegetative stage and more than twice lower in the oil obtained from plants harvested at the beginning of flowering and at full flowering.

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