Well, I’m glad it was helpful.
Thumbs up that they grow well. The description from the Ukrainian site gives frost hardiness up to minus 30°C, which is quite hardy of course. But long ago when I studied as an exchange student in Kobenhavn, I used to know a Finnish girl and when I once remarked that it was rather cold she told me at her place temperatures went down to -40°C, so I hope you’re living somewhat closer to the southern edges of your country than she did 😉
If you’re interested in growing tree peonies in your country, perhaps it would be a good idea to try some P. rockii (hybrids). These are normally better suited to your climate I think and you will know them from their dark flares at the petal bases. The rockii cultivars are also known as Gansu Mudan or Xibei Mudan, whilst the suffruticosa cultivars are known as Zhongyuan Mudan. Both are somewhat accustomed to rather dry climates, but suffruticosas prefer warmer climates compared to the rockiis. The species itself is usually white with the dark flare, the hybrids will have other colours as well.
All the best and good luck,