Going through a dusty 2003 hard drive I find this fantastic example of PET bottle-on-bottle planters at a gardening exhibition in Nagoya.
The top image features PVA glue planters. The middle image shows how to create flat floral wreath from 2L PET bottles and sturdy wire. The last image features upright 2L planters, with the fine touch of a bottle-in-bottle construction to store the watering can for the planter-sculpture. I think the cut-away bottle hanging from the bottom is a scoop for soil and fertilizer.