I would be hesitant to build a fence with just dirt packing the posts, especially if it was anything other than a split rail fence. I wouldnt put up a privacy fence with a 6" hole packed only with dirt.
tough to effectively pack the dirt back in with that little room. If you are going to backfill with dirt instead of using cement you HAVE to be able to compact it well.
We're definitely setting the posts in concrete. Plus in a matter of a few years I can only imagine the posts would begin to rot if they weren't set in concrete.
The PO of my house put in a fence with hole that look like this - the fence posts haven't exactly held up too well. I would be paranoid to have a 24" deep, 5-6" wide hole holding up my privacy fence around here. I can only imagine that the frost line must be deeper up in Ohio.
Most of the holes are much wider than they appear in those pics where I put the rings around. I basically did that only to look nice, but the holes are FAR wider than 5-6 inches. We went about 30 inches deep on all the holes.