Hello David,
ginger lilies, (Hedichium) do vary in hardiness. Cultivars from species that naturally grow at high elevations are likely to survive our winters best. I think that 'Tara' came from a Nepalese plant. Many plants in the UK fail to come through winter as a result of the damp as much as the cold. There is a theory that a blanket of snow does a good job of keeping damp away from plants and protecting them. As for mulching, the nursery folk do generally recommend this and I would follow their advice, as long as you don't get damp, sticky mulch stuck in the crown of the plant. We may get a damp and cold winter that is actually more damaging than the last. However, you've already had great success with growing these, so exercising your own judgment has worked well so far!
Emma
gardenersworld.com team