Sandhill Farm built a greenhouse in rural Missouri using earthbags for the base of the wall structure. They chose a 30ft x 20ft area, centrally located among the gardens, with good southern exposure. After three days of earthbagging, they were ready to begin framing the top part of the walls. Light straw clay was used to insulate the north, northeast and northwest sides.
You can find out more about how they made this very functional, inexpensive greenhouse on this project page.
Link to previous blog post and video about the Sandhill greenhouse: http://earthbagbuilding.wordpress.com/2010/07/21/earthbag-greenhouse-at-sandhill-farm/