I move my citrus inside for the winter. It depends how cold your winters normally get, both in terms of the low temperature and the duration of time below freezing. I also do not consider Meyer lemons to be the most cold-hardy of citrus. They are not Key limes by any stretch of the imagination, but compared to the various cold-hardy citrus used by zone pushers (satsumas, citrumelos, etc.), they are cold-sensitive. Harvey lemons are more cold tolerant.