just for inspiration , here are our german stadiums for the worldcup : http://fifaworldcup.yahoo.com/06/en/d/stadium/index.html
I think all the fields will be real grass in the World Cup. There are several countries trying out FIFA sanctioned turf, but I do't think there will be any in the WC. Also, I'd be surprised if Germany actually used turf instead of grass for the Bundesligue.
that was my point but i forgot to post the answer...ZERO. if it's good enough for the WC, then it should be good enough for Houston. all grass all the time!