In my opinion perennials don’t like to be cramped in containers, they can’t reach their full potential in a pot. As @Hostafan1 says they are full grown, about 4’ tall and flowering in the second and subsequent years.
Gardening on the wild, windy west side of Dartmoor.
I sometimes try and keep some going in pots, for sale on open day, but they don't like it, never flower and usually end up on the compost heap, all sad looking
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In the sticks near Peterborough