Hyssop (Hyssopus officinalis L.) is an oil plant, acts antiseptically and stimulates digestion. It is applied both for curative and culinary purposes. Studies conducted in the years 2006–2008 were aimed at the effect of plant harvest term (mid June – plants in vegetative phase, mid July – beginning of flowering, mid August – full blooming, mid September – after flowering) and plant spacing (30 × 30, 40 × 40, 50 × 50 cm) upon yielding and quantity of hyssop herb. Studies were conducted at one-year plantation established from seedlings. Yield of fresh, dry herb and yield of herb without stems was significantly dependent upon the examined factors. Significantly greater fresh herb yield was obtained from plants after flowering (on average: 2.32 kg^.m^-2), just like the dry yield and yield of herb without stems. In the analysis of the effect of plant spacing upon hyssop yielding, it was revealed that the highest fresh herb yield (on average 1.47 kg^.m^-2) was from plants grown in the spacing of 40 × 40 cm, similarly to yield of the dry herb and yield of herb without stems. No significant effect of plant spacing was found on the contents of dry matter, L-ascorbic acid, chlorophyll, carotenoids, oil, tannins and flavonoids. It was demonstrated, however, that the harvest term significantly effects the contents of L-ascorbic acid, chlorophyll, carotenoids and essential oil in hyssop herb.

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