Qualitative and quantitative composition of the essential oil is subject to different types of variability. The aim of this study was to determine the effect of irrigation and harvest date on the content and composition of essential oil distilled from leaves, petioles and leaf blades of Apium graveolens L. var. secalinum Alef. Drip irrigation was carried out twice in the third 10 days of July and twice in the third 10 days of August. A single dose of water was 20 mm. The raw material was harvested on September 7 and October 17, thus collecting leaves after 120 and 161 days of plant growth, respectively. Irrigation increased the concentration of volatile substances in leaf blades (0.68%) and decreased the content of these components in petioles (0.24%). Celery leaves harvested in October contained significantly less essential oil (0.34%) compared to those collected in the first 10 days of September (0.53%). Monoterpenes proved to be the main fraction in the essential oil of leaf celery, limonene and myrcene being predominant among them. Most limonene (75.77%) was found in petioles of irrigated plants. Leaves of irrigated plants contained more limonene and less myrcene compared to leaves of non-irrigated plants. More myrcene and less limonene were determined in leaves harvested in September than in those harvested in October.

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