Quote - I don't think it's worth the time it to use Indirect lighting with lots of plants. You probably won't be able to finish the render. If you really need it up close, then render the background without it, set that as a backdrop and render the foreground with it.

I just figured that I could do this :
uncheck the visible box for the objects in the foreground, make a render of the background ; paste as a picture, then render just the foreground, will the result be realistic enough, I'm concerned about shadows specificaly ?
YA