The usable part of leaf celery consists of the intensely green leaves with strong aroma, used for seasoning when fresh, dried, or frozen. The plants form from several tens to one hundred leaves, which can be cut several times during vegetation. The studies conducted in the years 2006–2008 were aimed at assessing the response of leaf celery to additional irrigation in the periods of humidity deficiency in the soil. The celery seedlings production was started at the beginning of March, the plants were put into the field in the third decade of May, in the spacing of 25 × 25 cm. Leaves were collected twice: in mid August and mid October. A significant effect of watering upon the height of plants was demonstrated, as well as upon the total celery yield quantity, nitrate (V) and total chlorophyll contents. Irrigation contributed to the increase of petiole weight share and decrease of leaf blade share in the weight of whole leaves. No effect of irrigation was found upon the number of leaves, total sugar content in leaf blades, as well as upon the content of essential oil in the whole leaves. A factor that significantly modified the leaf composition was harvest term. It significantly influenced the total sugar content, as well as the contents of nitrates (V) and essential oils in celery leaves. During the first harvest, conducted in mid August, the leaves contained less total sugars, whereas there were more nitrates (V) and essential oil.

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