What a great example of repurposing, but do they work? I have researched a bit and asked school gardeners that use these greenhouses if they do work.
They can with the right design.
The following sites are the best resources I have found on building plastic bottle greenhouses:
Andru Lensmaster has been blogging about his greenhouse since 2009. He provides loads of design ideas, links, and data on how effective his greenhouse works in the chilly UK.
Blue Rock Station in Ohio has created a 32 page guide called Building a Plastic Bottle Greenhouse available for $5.
These school garden coordinators had the following to share about their plastic bottle greenhouses:
Kealy Rudersdorf, garden coordinator at Stoddert Elementary in Washington DC told me to get their original design to work better they needed to insulate their plastic bottle greenhouse by lining it with plastic and filling openings between the walls and ground/roof with straw. She mentioned if she was to rebuild it she would have two walls of plastic bottles with hoop house plastic in between.
Mim Michelove of Ocean Knoll School in Encinitas, CA told me that their bottle greenhouse is at least 10 degrees warmer inside and that the clear lexan panel roof helps hold in heat.
Share your stories or resources on plastic bottle greenhouses in the comment section below.