During the first half of the twentieth century, Soviet citrologists grew (sub)tropical plants in temperatures as low as minus 30 degrees Celsius – outdoors, and without the use of glass or any fossil fuel-powered assistance.
A similar system adapted from the Andes that I'm keen to try once I have homesteading land. One guy in Nebraska combines that with geothermal heating to grow citrus in extremely cold, windy prairie land: https://www.youtube.com/watch?v=ZD_3_gsgsnk
https://www.youtube.com/watch?v=Qvk7Sszh6fg
A similar system adapted from the Andes that I'm keen to try once I have homesteading land. One guy in Nebraska combines that with geothermal heating to grow citrus in extremely cold, windy prairie land: https://www.youtube.com/watch?v=ZD_3_gsgsnk
I found YouTube links in your comment. Here are links to the same videos on alternative frontends that protect your privacy:
Link 1:
Link 2: