Decks, Patios, Porches and Docks - Deck Posts - Below Ground or Above Ground?

I am building a deck using 6 x 6 treated posts. The post holes will be 38 inches below ground and require 10" of concrete at the base. That means that 28" of the posts will be underground.

Would it be better to fill the entire 38" hole with concrete so that the post rests on the concrete above ground? Seems like that would be better to prevent rotting of the posts but would take an enormous amount of concrete.

I live in Northern Virginia

Welcome to the forums! Posts should never be buried. Although they are rated for ground contact, they will eventually fail, and how will you repair it? Fill the hole concrete (best to use a sonotube for a form), and install a Simpson Post base, rated for ACQ and set your post on it. It keeps the wood from standing in water. Post bases come in a couple of styles, one you bury in concrete as you pour it, and the type you place on the concrete and affix using lag shields and lag screws.