You know, the dynamics of soil and in the ground are quite different. blending compost and soil, then mulching around your trees, with a fabric mulch or with an organic mulch, or both, should work beautifully. The key is to do the root work before you get the trees in the ground, getting good flat root systems with no tap root. If you don't do this up front, you are wasting your time rowing trees in the ground- and I am speaking from experience.