I've about half a dozen or so young but good sized willows to coppice.   There's another area not that far away which can flood occasionally, but because it's lower than the banks of the burn that floods it, it can hold water for maybe a day extra and as a result a few trees have died in it.   So I'm going to stick in a few willow whips to fill the gaps when I'm trimming out.   Where is the best place to take a cutting from, approximately what length and thickness w