I'm sure you've seen those plastic political 'vote for me' signs around.
I've found a good use for the ones they forget to take down especially the large 4'x8' size.
Since they are corrigated (air pocket) and weather resistant they make a great enclosure for plants.
One sheet can make one 2'x2'x4' high box or several smaller ones.
Use a box knife and score one side only and fold. Clear Duck Tape will hold it for the season then collaps for storage.
Looks nice if you remember to put the white backside to the outside of your box.
A removable top can be made from most anything to uncover for sunlight.