A lot of folks can't afford a full greenhouse, so here is how to make a mini one, didn't cost a whole lot. The tires are nice because they will capture the heat being dark and that helps warm the soil. The side flaps are shiny, and can be lowered or moved to track the sun. I think I grew tomatoes during winter, but this was over 15 years ago and my memory is measured in Kbytes rather than Gbytes. (?). This unit is pretty portable and you can set one up even if you are renting. Grow your own food. The green-to helps give heat to the wall in daytime, and the wall returns it at night and keeps the plants from freezing quite so quickly. Now, however we have a larger greenhouse, but it still needs to be expanded.