Just realized the deck builder down the street sets his posts in gravel, not concrete
I watched him fill the holes with 3/4 inch crushed stone and he said water drains instead of heaving the post up in February, so now I'm second-guessing my own pour and wondering if anyone here has gone the gravel route and had it hold up after a few winters.
My neighbor Dale did the gravel thing on his fence about six years ago and those posts have not moved once. He dug down about three feet, put in six inches of stone at the bottom, set the post, then packed more stone in lifts while checking plumb with a level. The big thing is you have to tamp each layer hard, not just dump it in, or the post stays loose. I poured mine in concrete two years before that and I already have one post heaving up near the gate. Come spring I am digging that one out and going the gravel route too. It goes against everything you hear about burying posts but the drainage argument makes sense once you see it work.