Dividing plants and shrubs.

Hi Sadie - can't answer the whole question but ... my references say that Cape Fuchsia would usually be divided Mar/Apr (presumably when you put them back outside after over-wintering frost-free - they're quite frost-tender) and cut back to a couple of inches above ground level. A 'hardy' fuchsia I personally wouldn't divide, just take cuttings (or layerings) and cut it right back to just above ground level around mid-March or after the last of the serious frosts in your area and it'll come away again from the base. I cut fuchsias back in the spring because of the risk of frost damage if they're cut back in very late autumn as the flowers start to fall off - I often have flowers still on fuchias into December. You can take fuchsia cuttings now (as I am) and over-winter them or stick what you cut off in the spring into the ground and watch a few of them take root! Hope this helps ...

Valerian can be cut hard back when it has finished flowering. I think you could divide it, i haven't got it but it's a tough plant. I also think you could divide the Polyganum.