Many of my plants spend the winter in unheated rooms. The temp stays above freezing in those rooms, but some mornings I can see my breath. Various plants react to this in various ways. The only generalization I can make is that most of them stay alive. That doesn't tell you anything because you don't know what plants they are, and I can't tell you the exact temps.
These kinds of observations are interesting, but because there are so many variables, and sooooooo many plants being cultivated as houseplants/permanent potted plants, they aren't useful for making generalizations about plants in general, or even the same kind of plant. For example, a tiny specimen in a giant pot next to another specimen of the same type of plant that is much bigger and in a smaller pot can't be compared to each other even under identical care and conditions because it's not an apples-to-apples comparison if the plant-to-soil ratio is so uneven.
Nothing wrong with any experiment, IMVHO, I do a lot of them. Just don't be too bummed-out if you kill your only copy of something, if you are experimenting that way.
Begonias don't stay alive for long if the soil dries out.
