My apple trees sit in a sand dune. One of the ongoing projects at my place is the replacement of sand with decent soil. When I originally planted the trees I dug out a bowl for each, and filled it with soil. Last year I dug out some large holes between the trees which you can read about here... earthworks-continued-or-learn-to-eat I've begun to join the islands of compost together so the eventually the trees will sit in a large patch of dark nutritious water retaining soil. Once the holes are dug I throw in some branches for some long term rotting. Up the other end of the row, I've done the same thing cutting a trench around the tree. Once the channels are dug, I fill them in with the composted stuff pulled from the two centre patches. These are now holes in the ground again, ready for fresh material to be thrown in. Here you can see the colour difference between the sand and the decent stuff.