A few updates since we have had low temperatures of 26°F. Some of the trees are planted in the lowest location of the property and suffered frozen newly emerged buds.
# 010 frozen buds at ground level, no damage higher on the plant.
#011 damage only at the lowest locations, hardiness essentially identical to #010.
#001 very little damage.
4 year old #128 no damage on own roots, slightly higher elevation (20"-24" higher). The majority of the survivors in the original test plot were severely damaged during the past Winter. This tree shows not damage and is clearly hardier that the others.
Poncirus in full bloom, higher elevation, no damage.
The most important determining factor appears to be elevation, in previous years Poncirus showed damage of about the same degree as the hybrids, determined by elevation on clear, wind free nights.