--- Can't say that I've actually done the posthole deal - but I've done something similar. To begin, I live in North Louisiana on a 1 1/2 acre lot; semi rural. Summers get pretty hot but I live in one of the lowest lying areas in town so moisture isn't much of a problem, and I'm lucky enough to have honest to God topSOIL 8" to 14" over sandy clay. Yes, beautiful, natural BLACK loamy soil ( I AM Blessed) But to get to my tale: my lot has fence rows on either side and I have probably 50 to 60 trees - 3 -80 to 100 year old oaks and 7 70 year old pines - I do keep the pine straw from decomposing . Some of the smaller trees; mixed hardwoods, cedars, pines, cherry grow in clumps and I take the leaves and biomass from my veggie garden and spread it around the bases of the clumps, especially in shady areas. I started this to encourage the night crawler population with the intent of getting some free fish bait - but the worms have been so productive that I started raising red wigglers for bait and leave the nightcrawlers alone - over the last few years I have noticed the grass naturally taking over the ground around the heavier tree areas ( much of the lot had been grown up pasture for years - I slowly cleared it by hand) and the worms have done a FANTASTIC job of areating and casting the lawn. After a good soaking rain I can walk across my lawn and actually feel the soil compress under my feet, my St Augustine is well rooted and mine is the last lawn in the neighborhood to go dormant whether by lack of rain or by the onset of winter - so I would put a great deal of faith in your post hole idea - probably will try it myself.
Thank you VERY Much for an amusing and informative website - now I know what I have to do to get rid of that pesky clover !!!