Let me preface by saying I haven't any practical experience. But I just finished reading
Gaia's Garden and the recommendation therein is to create a "guild" by surrounding an apple tree with daffodils and garlic around the trunk and then a big circle at the drip line (keeps out grass, it said). Then plant nitrogen fixers, aromatics, and mulch builders inside the big circle. I seem to remember comfrey and artichoke (if a std) for mulch builders (cut and use as mulch). Can't remember the specifics for the others -- clover? vetch? fennel? dill? I remember they should attract beneficial insects though. I'll have to go back and read it again.
I'm sure there are others here who can speak from actual practice.
