Preparing ground for apple and plum trees.

Both are equally tough varieties and would survive wind. But do be sure to stake the windiest location well and run some old hosepipe through the rope/string/whatever you use to hold the tree. This will avoid excessive bark damage from the tree moving back and forth.

Since the trees will be there a long time, give the holes the best you can. I dug mine out 2-3 ft deep where possible, gave the empty hole a good drink as sometimes its ages before rainfall penetrates that far. Then bung in old manure, some bone & blood meal and I also throw in some mycorhyzal (sp?) bacteria which encourages feeder roots. Add some soil then more manure, etc and a bit more water. Set the trees in their holes at the same height they sit in their pots, no deeper, no higher. And always firm in the soil well as you go. Air pockets are death to tree roots. I like to heavily mulch all my trees and water often the first few years unless you get heavy rain years. After that, they can cope on their own other than pruning and picking.