I don't often do the green house thing...because unless you know it's in DEEP shade it can fry the plants.
The one exception is I will sometimes put my pearlite and sand into an aluminum dis[posable cake tin, dampen the mix and put the whole thing in a plastic bag with some small holes punched in it and hang from a tree. If you hang close to the branches it won't get any sun and hanging it keeps the plastic off of the plants....but it looks awful and people wonder why you have this plastic covered cake pan hanging in your tree....
But it works!
Linda C

Hmmmm. Well my neighbors already know I'm nuts, and hanging a cake pan covered in plastic from the tree branches would give them something new to laugh about. Maybe I'll try it. :) Thanks.