I didn't cover my rosemary last year and it died. Of course, we also had a freak polar freeze where the temperature went to like 20 below zero. This year I purposely planted the rosemary in a pot instead of the ground so I could bring it inside if/when it gets too cold. Of course, I haven't yet determined what threshold is "too cold." It got into the low 20s at night at least 3 times this week. It was covered with a tree cover and seems fine. Since they are predicting a colder & snowier winter than usual, I probably need to figure out when to pull the trigger on moving it. Since I have the new gardening shed in place, Ive toyed with the idea of just moving it in there with a grow light on a timer for the winter. It will still get REALLY cold in there since it's not insulated but at least it will be safe from wind, snow, and frost....