Trim it hard back in spring … not just a little. Take it back so it’s only about 12” tall. You’ll get much stronger bushier growth and better blooms. 😊
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
I think so too, but the OP said it was just one plant. Possibly meaning it was bought as a single pot. My guess is it's three grown together in the same pot, like some of the descriptions posted above. I do wonder how these will be doing in 5 or 10 or 20 years' time, but maybe buddleia is tough enough to cope.
Doncaster, South Yorkshire. Soil type: sandy, well-drained
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
When you don't even know who's in the team
S.Yorkshire/Derbyshire border