Posted: 28/08/2015 at 10:16
It's best to move plants once they have finished flowering as then you can cut off the spent stems and reduce stress on the roots and foliage as they settle in again.
I have friends who garden on heavy clay and have carved their garden out of a former wilderness of gangly conifers, even ganglier birches, brambles and weeds. Apart from digging over new borders and gving a generous layer of muck and compost to their new beds their soil improvement regime consists of giving all the beds a generous layer of well rotted compost every autumn after they've moved any plants that need relocating, dividing or introducing and once perennial foliage has largely died down. The worms work it all in over the winter and the new shoots come through happily the following spring.
Their garden is 2.5 acres and they get the local council to deliver a truck load of municipal compost as they can't generate enough themselves. You could simply reorganise your bed in September and October while the soil is still warm and not too wet to be workable and then mulch in the same way in November and December using your own garden compost or bought in soil conditioner. You don't need to dig it in first apart from adding some to the soil when re-planting. Putting piles of grit under individual plants can have the reverse effect and lead to water collecting there in a sort of sump effect.