A walipini, or pit greenhouse — a South American trick adopted by some Amish. Dig a hole, put on a roof — greenhouse without heating.
Construction
Pit 2–3 meters deep, size as desired. North wall higher (insulated). South wall lower, with transparent roof angled toward the sun. Roof — double polycarbonate or glass.
How It Works
At 2 meters deep, ground temperature is 10–14°C year-round. Earth walls act as thermal mass. Sun through the roof heats air by day, earth releases warmth at night. Without heating: 5–10°C inside when -20°C outside.
Winter Growing
Spinach, lettuce, arugula, chard, radish, green onions. Anything that grows at 5–15°C. Not tomatoes or cucumbers — they need warmth.
Cost
Earthworks + roof + walls = $500–2,000. Regular heated greenhouse — $5,000+. Pit greenhouse lasts decades with zero energy costs.