"ameijers" wrote in message

It ain't a fencepost. On a deck, wood and dirt should never touch. You
need
a proper footer, sized for the frostline in your area, and the weight that
will be supported. Same store that sells deck parts will have the plastic
cone things to form up footers. Just bury them as indicated, fill with
concrete,

Correct advice. You can safely block up the deck using appropriate sided
supports and remove the post to dig the hole for the footers, then replace
it after it is cured. I extended the patio under my 12 x 16 deck and put
temporary supports while I removed the four on the outer perimeter.