All BrazelBerry® blueberries and blackberries are resistant to cold. However, just like other pot plants, the root ball needs protecting so it doesn't dry out in frosty conditions. So, at extreme temperatures it's a good idea to provide extra protection both for pot plants and exposed plants in beds. During long cold periods, you can generously cover the soil with bark mulch and add extra water. This helps prevent evaporation and drying out. If it gets extremely cold, you can move your pot plants into an unheated garage.
Also in spring, when your BrazelBerry® plants come out of their dormant state and start to produce new buds and shoots, you should protect them from late frosts. The easiest way to protect them from night frosts is to cover your plants e.g. with frost-protection matting. However, you must remove the covering during the frost-free daytime.