Quote Originally Posted by keith3267 View Post
Make sure the PT posts are rated for ground contact, not all are. Next, after the ground settles, go around to each post and pile dirt up at the base so it always sheds water away from the base of the post. Do this at least annually for a couple of years. Eventually it will harden up enough to keep the post dry all the time.

If you decide to do concrete, and I personally do not see an advantage to it, fill most of the hole with your dirt, tamp it down good, then just fill the top two or three inches with concrete and taper it from ground level at the soil surface to about an inch up the post at the post.

So the short story is, keep water from pooling at the base of the post and you will be OK.
The only thing i might add to this advice, particularly the angling of any concrete away from the posts, is the use of copper naphthenate on any cuts you might make. We had to rebuild a trellis that was taken down in an ice storm (which was meant to support masses of vines and resist the occasional ice storm and hurricane) where we (probably) over built it by cementing the bases and treated the posts with c.n. where they were cut and/or come in contact with the cement. It's only been five years, but the structure seems as sturdy as when it was new.