Foliar application of different plant-growth regulators: phenylurea cytokinins (4-PU-30 and thidiazuron) and 2,3,5-trijodbenzoic acid (2,3,5-TB), paclobutrazol and jasmonic acid, was examined for their influence on the productivity and composition of the peppermint essential oil.

The following regulators have increased the total yield of fresh aboveground mass (two harvests a year): 4-PU-30 by 48.09%, thidiazuron by 40.49%, jasmonic acid by 37.96% and 2,3,5-TB by 34.42%. The stimulating effect of jasmonic acid became more obvious in the second harvest. Only paclobutrazol caused a slight decrease in the fresh mass.

All investigated regulators improved the essential oil productivity. The content of essential oil from air-dried plant material varied from 1.60 to 2.20%, as compared to the control 1.00%. As a result, the essential oil yield compared to the control significantly increased in all variants by: 187.08% (4-PU-30), 186.30% (jasmonic acid), 177.00% (thidiazuron), 126.49% (2,3,5-TB), and 35.53% (pacrobutrazol). GC analyses of essential oil composition demonstrated that qualitative oil alterations relate only to changes in the proportions of the main components: menthol, menthone, cineole, menthyl acetate, isomenthone and menthofuran.