Cold-hardiness varies widely between blueberry cultivars, so it's difficult to tell how hardy the plants might be w/o that info. Even if the species is known, how hardy a plant might be depends on what was transmitted genetically from the parent plant and other cultural conditions. I've provided a link that will be helpful if you know the cultivar. Be sure to add at least 1 full zone number to the purported hardiness of the selected cultivar as a guide to likely hardiness when growing plants in containers that receive minimal additional protection.

If the container is not too large & unwieldy, burying it to the soil line and mulching is a good method of providing additional protection from freezing lows.

Al

Here is a link that might be useful: Some possible help