As well as plants, pots (especially terracotta) are prone to cracking and breaking during the cold. This is because water can enter cracks and gaps in the terracotta and freeze if temperatures are low enough. Upon freezing, expansion occurs which puts pressure on the pot. Repeated freezing and thawing of this water can eventually put too much stress on the pot and cause it to break. We recommend insulating your plant pots or bringing them into a conservatory or greenhouse during colder periods.