So I have to draw SpriteBatch with enabled blur shader or draw rectangle with shader over previously drawn layer?

I'm writing tile-based game. Level contains few layers. I want to blur layers beneath player but I can't find any explanation how to blur screen. I am thinking of something like that process: - Draw layer 0 - Draw layer 1 - Draw layer 2 - Blur whole Screen - Draw layer 3 (with player) - Draw layer 4...