Objective – to determine rhythms of phenological development of Iris domestica Goldblatt & Mabb. in the collection of the Krivyi Rih Botanical Garden of the NAS of Ukraine for the assessment of prospects of their cultivation in conditions of the Right-Bank of steppe Dnieper. Material and methods. The material of the study was the plants of the I. domestica collection fund of the Krivyi Rih Botanical Garden, grown from the seeds of their own reproduction. Phenological observations in 2012–2016 were conducted according to the generally accepted method of phenological observations in botanical gardens of the USSR (1975). The dates onset of the development phases was translated into a conditional day from March 1, according to the method of G.N. Zaitsev (1978). Results. It was found that in our conditions vegetation begins in the II-III decade of March with the accumulation of temperatures above 5 °C from 8 to 22 °C. The period of budding occurs in the II-III decade of June in the presence of the sum of active temperatures above 10 °C from 574 to 672 °C. Flowering begins with the III decade of June – I decades of July in the presence of the sum of active temperatures above 10 °C 596–794 °C and ends in the I-II decade of August for the sum of active temperatures above 10 °C from 1088 to 1311 °C. The vegetation period of the plant ends in the I decade of October – the III decade of November. Conclusions. It was established that in the conditions of Kryvyi Rih I. domestica undergo all phases of phenological development, which are characterized by a wide amplitude of their onset and depend on the accumulation of the sum of active temperatures. The variability of the seasonal rhythm of development suggests a sufficient degree of adaptation of the species to the climatic conditions of the Right-Bank of steppe Dnieper and the potentially high ability of their successful growth in the region