Any concrete is a "free-dug" hole will have a rougher surface and can heave even with less than 36" of frost because the frost/soli can grab it and pull it upward.
The best route is Sonotubes to the frosr depth or a "bigfoot" at the bottom to spread the post loads out over a larger are (good for pooer soild), plus you get a larger base area to resist heaving.
Dick
The best route is Sonotubes to the frosr depth or a "bigfoot" at the bottom to spread the post loads out over a larger are (good for pooer soild), plus you get a larger base area to resist heaving.
Dick