I’ve lost almost all poncirus hybrids when temps reached 5 degrees F and below over several years. Also lost 10 ft tall dunstan and swingle citrumelos when temps never got above freezing, hovering at or just below 32 degrees F for a week. I lost hybrids when they just started putting out new growth in March, when we got a low of 14 degrees, and these were protected in a high tunnel with water barrels next to each tree. The only hybrids that have survived at my place outdoors without being covered and heated by space heaters for the past decade are Dunstan citrumelo, citradia, and Thomasville citrangequat, and they have died to ground and came back from roots several times. I’ve lost several Dunstan and citradia trees too, but these are the only three specimens that I have left. I’ve lost the following over the years: Dunstan, swingle, citradia, rusk, Changsha, mortan, Nansho dai dai, ichangensis, Ichang lemon, carizo, yuzu. I’ve even lost some potted flying dragon one-year seedlings when zero degrees F all night two nights in a row. The small cracks at base of the tree trunk in spring means the tree is going to die; I had a citradia leaf out in spring despite a crack in base of trunk bark and it died suddenly soon after.