I went to the painting section and picked up the thickest black
   plastic I could find that was the right size. Forget the "weed
   blockers" - weeds grow right through it. Eve with this plastic -
   any holes you punch through (for the metal U shaped things that
   hold it into the ground) - will grow weeds through it. And when
   the season is over, I plan to crumble it up and throwit out --
   as much as I hate waste - because I think it won't last 'til the
   next season. Besides, I want to rototile it again, and the
   plastic is cheap enough to replace. "