Or should I do something to enable it? thank you!!

They enable themselves. And you can't disable them once they're in.

Remember, it's shadows on grass, not grass casting shadows.

Yes, something other than Grass has to be around to cast the shadow.

oh i get it now thanks for clearing that up guys, i thought it was the actual grass casting shadows not something casting shadows onto the grass. also i didnt know that shadows wernt allready cast onto grass

That's pretty obvious. As if Grass would have the magical abilities to cast anything... pssshhh.