A lot of people have been asking about the Northeastern United States upcoming November lows. Should you be worried about your fig trees?
Personally I think these temperatures are IDEAL because that will quickly send our fig trees into full dormancy. Especially when combined with a hard freeze. It's not until you get below 17 that you should even consider worrying. I'm expecting after these lows that I'll be able to prune, root prune and put them away for good. If you prune or root prune before the sap flow completely returns back to the roots, you're in a sense hurting your tree and losing some benefits of the dormancy process, which by cause and effect should get you off to a weaker start in the spring due to less carbohydrates stored in the roots (at least that is my theory and I'm sure it could be debated, but I don't think we'll ever really know for sure). People can talk all about figs not needing a dormancy period (which they don't), but we are lucky to have such a process. Putting them away early is likely not going to hurt anything, but I feel like you're babying your trees. Let them get stressed and withstand the elements. They adapt, become stronger and the fruits taste better that way. At least not in this sense, but the fruits will taste better when your tree is deficit irrigated and slightly stressed.
My pruned Smith and 20+ other pruned potted trees survived Thanksgiving night last year with absolutely no damage. It was 14 that night. I even had thermometers out there to document. Aaron Delmanto and Mario have experimented with these lows quite a bit. I know Aaron has killed quite a few trees pushing the limits and came to the conclusion that 17 was the safe point. The roots around 12-15 start to take damage and well... if the roots die, the top follows. The roots of fig trees are a lot hardier than we think. Another example... last winter I planted two trees with their root balls above grade in a 1 ft high raised bed. I think we reached somewhere around 0-2F last winter at the lowest. Both of these trees took some top damage, but are now back in full swing. I don't imagine that the root zones of these trees got too low because I had insulated them the best I could, but it does add to the argument.
Here's where some of you may differ from myself: What you should be worried about is unlignified green growth. That new growth is gonna get toasted and some of your hardened, but not fully lignified green wood may take some damage as well. Who can say at what temperature that wood will be affected because it depends on the variety, how far along the wood is in the lignification process, and probably a few other minor things. This is where people with big beautiful overfed trees really struggle. This is something you should have taken care of 3+ months ago by slowing down the growth. IF you're one of those people with big beautiful overfed and babied trees, I would probably not let them go below 20. I really couldn't say, but your trees probably will not be able to withstand what mine can. I did have a very large Moscatel Preto (in fact it was the largest tree in my collection), which I had semi-buried in the ground. This tree was overwatered and was overfed for pretty much the entire season. I don't remember exact temperatures from that year, but it certainly wasn't below 20. The following season.. my Moscatel Preto was now my smallest tree. That frost I suspect (I don't know for sure) killed my tree all the way down to the soil level and while Moscatel Preto is known to be one of the least hardy varieties (like Smith), I believe the large contributing factor was the fact that it was a overwatered and overfed tree with growth that wasn't fully lignified. That frost I suspect ruptured the cells during the freeze thaw cycle, which usually isn't an issue if you have the right amount of water stored in the branches.