Sherry, I know what you mean by "cold sinks". I grow a lot of lantana (deer proof), and also pelargoniums (*not* deer proof
). Every winter they both take a hit, and if the winter is cold enough, I can lose the in-ground pelargoniums. Half a mile away, on a sunny, flat, and level street, the lantana is in bloom all year long, ditto the in-ground pelargoniums there. The only difference I can think of is that we are down in a dip, with hills rising on either side of us.