Wow, that method right there is the way to go for free users. That's what I like best about Construct is how you can make almost anything work in many different ways.
If sprite isn't overlapping tiled background then spawn and move on. If overlapping tiled background then don't spawn and move on. Could use this method for rocks and lakes too.
I have a GlobalVariable set to 0. Every 1 second this number get's changed to a random number between 0-100. If it's <=5 then the group that spawns the grass is toggled once. But obviously I couldn't do this due to not knowing how to target a single instance of the silly tiled background.
So thanks again, you have been of much help!