work in progress

By digging below the frost line, and using materials with high thermal mass to build the retaining wall (stone, earth bags) these greenhouses are able to retain heat from the sunlight and release it much more slowly at night. Storing organic material, like manure or compost, provides sufficient carbon dioxide for plants while warming the space.

https://www.motherearthnews.com/organic-gardening/essential-tips-for-building-a-durable-walipini-greenhouse-zbcz1706