Tomatoes prefer nights above 55Â°, but nights in the 40s won't hurt them -- they just won't ripen fruit, or will ripen very slowly. So if you cover them, radiated heat from the earth will be held around the plants and they'll ripen sooner.
I've read that tomatoes won't set fruit at temps below 47. I'm sure some expert got paid a fortune to figure that one out However, I am babying one through winter in the greenhouse to see if I can get early fruit. Our coldest night so far has been 28 Frost outside, but I think not in the greenhouse.
If you are expecting another warmup, I'd say cover it with remay/leaves/straw or tent them with hot water bottles. Good luck!
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