That depends on the type of cactus. Some cacti like the Prickly Pear can survive freezing temps and others suffer when temperatures go below 45 degrees. It also depends on how long the cacti has been able to become acclimated to the cold before a freeze hits. It is usually the wet rather than the cold that kills cacti outdoors so plant under the eaves of a house or in a pot that can be sheltered from winter rains. Keep growing, Marianne Binetti