I have a fairly large rectangular box that I am going to recycle into a planter (in its former life it was a tool box for the truck). If I fill it full of soil, it's going to be way too heavy. Any suggestions of what I can put in the bottom 2/3rds instead of soil to fill it up? Thank you.
Foam packing peanuts are a classic for taking up space in large planters. Also if you use a soil that is mostly perlite then you reduce the weight by a great deal. A really large outdoor container can safely be 50% perlite.