I just attended a talk by a pro estate maintenance gardener--she said, over and over, "March and October, grab it like hair and cut off half." General advice for most perennials here.

Having said that, Echium cadicans-- prune flower stems off after flowering to tidy up the plant and cut back hard in late fall to reduce size and encourage new growth from lower branches. Good to wait until you see a little bit of new growth appearing. The plant will produce new blooming stems for next year. An established Butterfly bush, whack away, it will all grow back. Ivy Geranium, cut back hard but leave some foliage so the plant can feed itself. Calandrinia (now Cistanthe) I find best re-rooted from cuttings when it looks ratty. Or just cut off anything that looks bad--it resprouts new growth readily, but again doesn't look as good as a fresh plant.

I agree about the calandrina. Those beds need replanting from cuttings every few years.

Thanks! I love the hair cutting image. Annies Annuals has a video covering this subject...Hope it opens for you.

Here is a link that might be useful: Cutting Back & Cleaning Up