[basjoos]

I guess you could consider my cold frames to be a passive solar mini-greenhouse. I build them over my vegetable beds to keep them producing all winter. They are 4 feet high at the front, so I can slip inside them to weed and harvest vegetables in comfort on a cold sunny winter's day. They have a row of gallon milk jugs filled with water for heat storage along the back, vertical south glazing, and a sloped north-facing roof made of foamboard. As the winter progresses they become populated with toads and tree frogs taking advantage of their warmth and insect supply. In my climate, they maintain above freezing inside down to around 8F and self-sown tomato seedlings will keep growing slowly in them all winter.