I have only four trees in the ground. Two are in a flower bed on the S. side of my house and benefit from the warmth radiated by the brick walls. Two more are on the S. side of my metal barn, which is as cold as a witches teat in the winter.
Those in front of the house are a Celeste and a Joe Morle Paradiso; the Celeste two years in the ground, the Paradiso three years. The Celeste was cut off to barrel height, a barrel put over it and the barrel packed with straw. The Paradiso was cut off as well, then packed with leaves raked off the lawn. Both trees survived the -15F temperature we endured this winter, but the Paradiso (that packed in leaves) is coming out more quickly and vigorously than the Celeste.
Out by the barn were a Hardy Chicago and a Pakistani Black, the UCD fig. The HC is going into its third season, the Pak is going into its second season in-ground. They are about the same size. The HC was packed in straw inside a barrel, the Pak Black was trimmed to half-barrel height, covered with soil and a half-barrel put over it. The unheated barn provided protection only from the wind. Both trees exhibit much freeze damage, some branches killed to the ground but some alive and sprouting. Interestingly, the Pakistani, that covered with soil, suffered more damage and is coming out more slowly than the HC.
I have to conclude that (1) older trees are more frost resistant, (2) Leaves are better insulation than straw, (3) HC is one tough little tree and (4) it takes a lot of dirt to cover a fig tree so that it will tolerate sub-zero weather.
Ox