Well, I have not tried the tea-light trick. Some prepper forums even suggest this to keep your house warm if the power goes out (as in, above freezing, not comfortable warm). When I had a hoop-house for a greenhouse I did use a 100w incandescent lightbulb on a timer to keep the greenhouse above freezing. It extended the growing season by around 2 months even when we had a few inches of snow on the ground. I also didn't have to keep going out daily to set up new tea candles which was a plus. Archive: https://archive.today/mzBLg From the post: "It is a common suggestion amongst greenhouse people that a long burning tea light inside an upturned terracotta pot can be enough to keep frost away from plants. Is this possible?"