This can vary a lot depending on amount of use, amount of sun the area gets, local vegetation, etc. Power wash it any time it starts to look dingy or you see mold growing.
Really just depends on your personal tolerance for dirt and grime. We power wash pool decks quarterly for some of our commercial customers, but I'm sure they dust them off more frequently than that. Our service is more of a deep clean with high-pressure steam and hot water.
This can vary a lot depending on amount of use, amount of sun the area gets, local vegetation, etc. Power wash it any time it starts to look dingy or you see mold growing.