I'd try moving them in autumn if it's not possible to wait until spring, rather than chucking them out and starting again. Cut the perennials back first so they put their energy into getting the roots down not trying to set seed. Water well before and after, until the end of the growing season unless it's very wet, and move each one in as big a lump of soil as you can manage. You could also put some pieces in pots.
Doncaster, South Yorkshire. Soil type: sandy, well-drained
Thanks all for the advice, I did move and divide some bergenia this morning, fingers crossed they will be alright.
I’ll have to move the plants but Ill divide them in the spring, hope I don’t lose them as I was hoping to divide them and have enough six hills giant to line a path.
I have successfully moved Six Hills Giant in the summer months. Water it well beforehand, cut it back hard, take it by surprise, chop it into smaller pieces, and water well in its new location.
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Is it Nepeta in your pic?
Luxembourg
Yes have six hill giant, a couple of hydrangeas, and some achillea.