Designed/developed at the University of Minnesota, this passive-solar Deep-Winter Greenhouse (DWG) utilizes the sun's energy (instead of more traditional heating sources) to grow crops during the winter months. The building sits in an east-west position, with its glazing (triple polycarbonate) wall facing south. During the day, the sun heats the inside air, and a fan blows it underground through drain tile to be stored in a thermal-rock bed. When temperatures in the DWG drop to 38º, a thermostat triggers the same fan into reverse, pulling the stored heat out of the thermal bed back through the tile and into the building. A DWG can be used to grow crops that thrive with minimal light (e.g., lettuces, herbs, brassicas, Asian greens, sprouts), providing year-round production for small-scale farmers and gardeners.