The influence of vegetation period length of cardoon plants (Cynara cardunculus L.) on herb yield and its pharmacological value conditioned by chemical contents in air dried herb was examined in the research. The research conducted in the years 2009–2011 included valuation of total phenolic acids as equivalent to caffeic acid, flavonoids and tannins content in plants during their vegetative growth. The effect of the vegetation period length on cardoon plants yield was observed. The content of polyphenolic acids (caffeic, chlorogenic and cynarine) was marked with a performance liquid chromatography (HPLC).The contents of biologically active compounds depended on plants age – the most phenolic acids were noted in herb harvested from plants 120-days and 150-days old (1.86–2.58%). Herb obtained from plants of different age contained from 0.38 to 0.43% flavonoids. More tannins were accumulated in young cardoon plants after 90–120 days of cultivation (3.72–3.43%) in comparison to plants 150-days old (3.25%). The content of caffeic acid, chlorogenic acid and cynarin in cardoon herb depended on length of vegetation period of plants. The content of phenolic acids in leaves increased with time. Values of correlation coefficients indicate significant correlation of total phenolic acids and tannins content in cardoon herb. The higher content of total phenolic acids the lower content of tannins (R = -0.88). Strong correlation was noted between the content of total phenolic acids and the content of chlorogenic acid (R = 0.67) and caffeic acid (R = 0.78). On the basis of the results of the presented work it could be stated that cardoon leaves are a valuable material for herb industry.

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