Paeonia parnassica is not easy in cultivation. The best ist pot culture.
I have a 6-year old plant, I hope for the first flower in 2020 or 2021. And a young plant too.
I have my plant in a pot under glass from october to march. The other time half-shade near my house with protect again summer rain.
Soil is 3 parts potting soil, 1 Seramis, 1 Perlite, 1 Aqualit and 1 Sand. Good drainage with lime stone.
Be carefully with watering. A bit more in Spring and first time of Summer, when the leaves faded, only small.
Temperature in Winter 0-5 C.