I have a 10-year old escallonia in my hedge (1), North facing, hillside, exposed, in Sheffield. I did a tidy-up three years ago and found it had produced several rooting stems which I cut off and potted. All did well except one which died, so I decided they were hardy, and planted three beside my garage to screen it (2,3,4), also North facing, one against my house front wall (5), East facing, and one against the same wall but in an angle caused by the porch, so it is East and North facing, but has no southerly aspect (6). All did well and grew vigorously until the recent snows. After that 1,2,3 & 6 are still fine, 4 & 5 have extensive die-back, 5 in particulars has branches broken by snow. Now the frost is gone I will cut out all the die-back and see how they fare, but clearly hardiness is variable, even amongst siblings. It is interesting that 6 is the least vigorous grower, maybe as it gets least light, but was totally unharmed.