Is it possible to grow a plant outdoors in the winter? Better yet, is there a strain designed for low temperatures? Could i use a small greenhouse or something?
It is possible. If you live where it snows it becomes more difficult of course. You would need to supplement heat. Growing in a greenhouse in the winter takes a inside nursery or vegg room. You would have to vegg them to 2-3 ft plus before you put them in natural sunlight as they will go straight to flower in a couple of weeks with how many hours of sun there is or you will need to supplement light too. Depending on how much sun your area will get will determine the density and extra length of flowering time.
It is possible to veg and flower using only Winter sunlight(obviously with modified temps), I did so last Winter indoors. However, without supplemental lighting you will most likely have stretch issues and fluffy bud.
At least that was my experience, now I supplement lighting b/c Winter sun isn't really good for vegging to begin with. I think it's the wrong spectrum.