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.

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. | Мета. Установити особливості сезонного ритму росту й розвитку сортів півоній Itoh Group в умовах Національного ботанічного саду імені М. М. Гришка НАН України (НБС).Методи. Об’єктом досліджень слугували рослини 24 сортів півоній Itoh Gp. Дослідження проводили на експериментальній ділянці відділу квітниково-декоративних рослин НБС протягом 2017–2020 рр. Суму ефективних температур обраховували через сумування добових температур повітря, зменшених на значення біологічного мінімуму.Результати. Виділено фенологічні фази росту й розвитку рослин півоній Іто-групи. Побудовано фенологічні спектри для різних феногруп. Установлено, що цвітіння ранніх сортів – ‘First Arrival’, ‘Hillary’, ‘Julia Rose’, ‘Morning Lilac’, ‘Old Rose Dandy’, ‘Sonoma Apricot’ – розпочинається за суми ефективних температур ≥ 400 °С. Сорти рослин середньої групи зацвітають, коли сума температур сягає 450 °С. До цієї групи належать ‘Bartzella’, ‘Callie’s Memory’, ‘Cora Louise’, ‘Lollipop’, ‘Scarlet Heaven’, ‘Sonoma Velvet Ruby’, ‘Yellow Dream’, ‘Yellow Emperor’, ‘Yellow Heaven’, ‘Yellow Waterlily’. Пізньоквітуюча група включає сорти ‘Border Charm’, ‘Garden Treasure’, ‘Kopper Kettle’, ‘Pastel Splendor’, ‘Prairie Charm’, ‘Viking Full Moon’, ‘White Emperor’, ‘Yankee Doodle Dandy’, необхідною умовою цвітіння яких є накопичення ефективних температур понад 500 °С.Висновки. Рослини сортів півоній Itoh Gp успішно проходять усі фази сезонного розвитку та встигають завершити вегетацію. За тривалістю вегетації вони належать до весняно-літньо-осінньозеленого феноритмотипу. Настання відповідних фенологічних фаз у півоній досліджуваної групи сортів потребує певної суми ефективних температур. Відростання сортів розпочинається 23 березня – 2 квітня, коли сума ефективних температур змінюється в межах 20–40 °С. Цвітіння сортів характеризується як пізньовесняне, триває 9–16 діб ± 3–4 доби й залежить від сортових особливостей рослин та року вирощування. Швидке наростання суми ефективних температур до 700 °C під час цвітіння рослин скорочує його тривалість на 4–5 діб. Аналіз фенологічних спектрів сезонного розвитку рослин дав змогу виділити сортимент ранньо‑ (22–25 травня ± 2–3 доби), середньо‑ (26–28 травня ± 3–5 діб) та пізньоквітуючих (29–31 травня ± 4–6 діб) півоній Itoh Gp, що забезпечує безперервність їхнього цвітіння загалом упродовж двох місяців.

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.