Here is what the care guide on the Empire says:

The pomegranate needs a warm sunny and airy place over the growing season. In hot and dry climates pomegranate bonsai in small pots should be protected from hot afternoon sun in summer. On the other hand they must also be protected from frost. A frost-free cold frame with temperatures between 2 and 8° C (35 – 46°F) is an ideal place in winter.