Purpose. To analyze the variety diversity of the Itoh peony group in the collection of the M. M. Hryshko National Botanical Garden National Botanical Garden National Academy of Sciences of Ukraine and determine its biological features in the new conditions of introduction. Methods. Introduction studies, phenological observations, morphometry, statistical processing of results. Results. The cultivars diversity of the Itoh peony group of the M. M. Hrysh­ko National Botanical Garden National Botanical Garden National Academy of Sciences of Ukraine collection was analyzed. The ornamental properties of the cultivars were described. Features of their growth and development under conditions of introduction were studied. It was revealed that the duration of vegetation of plants of Ito group varieties is 218–225 days. It was determined that plant growth begins on March 23 – April 2, flowering on May 19–28. The budding of plants was observed in the first decade of May and lasts 16–20 days. It was revealed that in the conditions of introduction ‘Morning Lilac’ and ‘Sonoma Apricot’ bloom first (May 19–20), ‘Viking Full Moon’, ‘Yankee Doodle Dandy’, ‘Yellow Waterlily’ bloom later (May 28). The height of generative shoots of plants in flowe­ring phase ranged from 60 to90 cm. Plants go dormant in winter, having formed generative shoots that successfully winter. Reproduction of plants occurs both due to the buds that form on the lower part of the stem, and the buds that form on the rhizome. The shoot-forming ability and flowering productivity are 6.0±2.5 – 19.5±4.0 shoots and 4.5±1.5 – 16.0±3.0 generative shoots per plant, respectively. Cultivars ‘First Arrival’, ‘Sonoma Apricot’, ‘Hillary’, ‘Bartzella’, ‘Morning Lilac’, ‘Lollipop’, ‘Old Rose Dandy’ are highly productive. Conclusions. The collection of peonies of the M. M. Hryshko National Botanical Garden National Botanical Garden National Academy of Sciences of Ukraine has been expanded by Itoh Group cultivars. The R. Anderson’s breeds of 1980–1990 are more fully represented. An analysis of the ornamental features of the varieties showed that the hybrids with a semi-double flower shape of a yellow color dominate the collection. Cultivars retain all their ornamental and economic characteristics under conditions of introduction. The Itoh group varieties of the collection can be material for developing technologies for their cultivation and propagation, can be a source of replenishment and expansion of regional botanical gardens collections, planting material for gardening and landscaping, and also perform an educational and cognitive function.

Purpose. To reveal the peculiarities of the seasonal rhythm of growth and development of Itoh Group peony cultivars in the conditions of the M. M. Hryshko National Botanical Garden National Academy of Sciences of Ukraine. Methods. The objects of research were plants of 24 cultivars of Itoh Group peonies. The research was conducted on the experimental field of the Department of Flowering and Ornamental Plants of the M. M. Hryshko National Botanical Garden National Academy of Sciences of Ukraine during 2017–2020. The sum of effective temperatures was calculated by summing the daily air temperatures reduced by the biological zero. Results. The phenological phases of Ito Group cultivars growth were determined. Phenological spectra for different groups are presented. It was determined that the flowering of early cultivars: ‘First Arrival’, ‘Hillary’, ‘Julia Rose’, ‘Morning Lilac’, ‘Old Rose Dandy’, ‘Sonoma Apricot’ starts at the sum of effective temperatures ≥ 400 °С. The middle group hybrids bloom when the sum of temperatures reaches 450 °С. This group includes: ‘Bartzella’, ‘Callie’s Memory’, ‘Cora Louise’, ‘Lollipop’, ‘Scarlet Heaven’, ‘Sonoma Velvet Ruby’, ‘Yellow Dream’, ‘Yellow Emperor’, ‘Yellow Heaven’, ‘Yellow Waterlily’. Late flowering group includes: ‘Border Charm’, ‘Garden Treasure’, ‘Kopper Kettle’, ‘Pastel Splendor’, ‘Prairie Charm’, ‘Viking Full Moon’, ‘White Emperor’, ‘Yankee Doodle Dandy’; accumulation of effective temperatures above 500 °С is an essential requirement for their flowering. Conclusions. Itoh Group cultivars successfully pass all phases of seasonal development and manage to complete the growing season. Cultivars belong to the spring-summer-autumn-green phenorhythmotype. The onset of the corresponding phenological phases in peonies of the studied group of cultivars requires a certain sum of effective temperatures. Plant outgrowth begins on March 23 – April 2, when the sum of effective temperatures ranges from 20–40 °С. The flowering of varieties characterized as late spring, lasts 6–9 days ± 3–4 days, depending on the varietal characteristics and the year of cultivation. A rapid increase in the sum of effective temperatures up to 700 °C shortens the flowering phase by 4–5 days. An assortment of early (May 22–25 ± 2–3 days), medium (May 26–28 ± 3–5 days) and late-flowering (May 29–31 ± 4–6 days) cultivars has been selected, what ensures the continuity of peony flowering during two months.