Back in 1977 scientists noticed a few of their interspecies hybrid tomato plants survived a frost! Upstate Scientist Is Trying to Breed a Tomato That Can Stand the Cold - The New York Times (nytimes.com).
While I direct seed many tomatoes I also grow many from transplant. The last four years I have noticed that May 15th our average date of last frost has been the latest it froze. Not so this year (2021), it got down to 30F at the Ronan MT airport weather station at 6:15 A.M. on the morning of May 22nd. Notably only at 3:15 A.M. did the dewpoint match the temperature- this is a good thing this was brief because frost forms on the leaves when the dewpoint matches the temperature and is much more damaging to leaf tissue than dry cold.
Of course I had already planted hundreds of tomato plants and many of those froze to the ground! However a few did not! Why not?
Some of my tomatoes are about 1/4 wild hairy tomato (Solanum habrochaites) the same wild species used by the 1977 researchers (who never actually managed to make the tomatoes they hoped for). Could this be a factor? Possibly however there are confounding variables!
In my gardens I have been adding sand to the soil, sand improves the drainage and causes the soil to be less wet, it may also absorb and radiate more heat. Some of the tomatoes that survived were growing in this added sand. Others may have had small bowl shaped depressions left around them after planting. I noticed that some of the survivors were in sand and some were very short. Taller plants were almost universally frozen in the lower gardens.
Notably only at 6:15 A.M. did the dewpoint match the temperature- this is a good thing this was brief because frost forms on the leaves when the dewpoint matches the temperature and is much more damaging to leaf tissue than dry cold.
More of the wild hairy tomato (S. habrochaites) descended tomatoes survived but they are a large portion of my garden and they occupy a isolation garden that seems favorably situated for frosts- less likely to freeze than some of the other isolation gardens.
I also covered about 35 or so of the most important tomatoes and in consequence those survived. Notably many of the lower gardens succumbed two days prior, on a night I did not think it would get cold enough to freeze.
Do I really think therefore that any of my tomatoes may have this near legendary frost tolerance? Not at all certain, but further investigations may be warranted. Stay observant!