This website has some ideas about building an earth bermed / sunken greenhouse. It may help extend the growing season for some folk whose location experiences shorter growing seasons than milder climates. Via: Build a $300 underground greenhouse for year-round gardening (Video) An excellent reference for earth sheltered solar greenhouses is Mike Oehler's book:- Via:The Earth Sheltered Solar Greenhouse Book: Mike Oehler, Ross, Anita Bedard, Katie Purviance, Cassie Eisenhower, Chandel Oyharsabal, Sarah Tye, David Fairall: 8601400860021: Amazon.com: Books Via:File:Oehler greenhouse.jpg - Open Source Ecology Greenhouses - Open Source Ecology
Bermed, rather than sunken below grade...though, if you look at Oehler's set up. because he has built it into a fairly steepish slope, the lowest point of the set up is close enough to grade to drain the cold sink with agricultural pipe reasonably easily. Otherwise, a sump and sump pump may be a work around.
Good idea to have a sump pump or drain set up because you don't want to drown your rabbits. jk Seriously- this is a really cool idea. Thanks for posting. Need to read more on this concept
There is an area on my place that might be just right for this kind of arrangement . I don't get enough rain to be a problem , as a matter of fact creating a reservoir might be the ticket just below the green house. If the rain water is gathered into a settling pond then filtered into the fish pond that water can be cycled into the garden. I get just enough wind that could drive a mill for circulating the water from the pond to the garden .