It dpends upon which rosemary's you have. Most of the tall upright types are very hardy, though if it snows alot you will need to clear it off the branches, several branches broke on my tall one when we had the heavy snow 2 winter ago. The low weeping or repens type - often called 'capri' is not particularly hardy, I keep it in a cool greenhouse over winter having lost it before. Possibly it will do with fleece and newspaper, tuck the pot near the house or uner a hedge. If in the ground, then peg some horticultural fleece over it when the weather demands.