I had one exactly like that, I sawed it down to about 6” teased out the roots, planted it out in the garden and in no time it became a beautiful bush and flowers well.
Gardening on the wild, windy west side of Dartmoor.
I've root pruned a little, and repotted it. From what you say It seems like I should prune the top as well, so I will have a go at that tomorrow. I must say, I was horrified when I finally got it out of the pot, I wondered how it has managed to stay alive like that. It even flowered fairly well this year.
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