Well "Lupins" in pots,
I'd leave well alone until they've finished flowering and then trim them down and then re-pot,
My own "Lupins" are outside and i trim them down after the first flowers and late summer i get a second flowering, its the seeds off this second show i keep after they've flowered and sow those seeds next spring.
Hope this helps.

Lupins like to develop a long tap root, and are much better planted in the ground, but they like a light sandy loam, well drained, they don't like wet feet, so if you have a clay soil, they're probably better off in pots. Derek.

Put them in the ground now - it will do no harm and help with keeping them moist during summer. I have clay soil and actually have a problem with Lupin self seeding and regrowing from roots derek - it is well drained clay I suppose.

Hi Kildermorie, I tried growing lupins for years on clay soil, not the really sticky stuff, just lumpy, and it was pretty well drained, but I always lost them in the first winter, eventually I dug out about a 4 ft square, x 18" deep, mixed soil and sharp sand and grit, forked over the bottom of the hole, and refilled with the mixture, I have had no trouble since, so for me they need a sandy loam, Derek.