Concrete may seem best but gravel's better in post holes
Not one but two good carpenters have told us, "Wooden posts
should not be set in concrete but in gravel. If you set them in
concrete even pressure treated lumber will rot at the top of the
concrete, affected by the water that pools there."
So, why did we let this very nice trellis be set into
concrete? Not even 6 years later both posts seem to have broken
loose. As predicted, at the top of the concrete.
We've braced them for now since replacing them requires
digging better done in finer weather -- to move all those nicely
established plants out of the way, extract the old supports
and put in new posts!