20 Greenhouses from recycled windows. OR visit WasteFreeSD.org for your one stop recycling center! Locate the nearest proper disposal site near you for random large objects like windows, doors, furniture...down to the little stuff like motor oil!
I did this because there is no digging in my rock solid ground. Did not cover the holes but use them for herbs and annuals. I also lined with weed barrier cloth and used rebar in several places for stability. I love it and makes maintenence super easy.