With few exceptions, cacti are susceptible to freezing temperatures. Once exposed to frost, various parts of a cactus can begin to rot, which often is the first step toward the eventual death of the entire plant. If frost damage is caught in its early stages, steps can be taken to avoid losing the plant.
Things You'll Need
Inspect the plant. Damaged areas of cacti often begin turning yellow, followed by a blackened spot, after being hit with frost. Using either your fingers or a pair of tongs, physically test the plant by applying pressure to the exterior of the affected areas. Extremely soft or mushy areas are a sign that frost damage has occurred.
Wait until any danger of freezing temperatures has passed. Parts of the cactus that are already damaged can serve as a temporary protection for healthier parts until temperatures are warmer and more stable.
Clean a sharp knife with a solution of 10 percent household bleach. Make a cut in any overly soft or discolored area of the cactus and remove the frost damaged parts. Clean the knife in the bleach solution after each cut.
Sprinkle powdered sulphur on the exposed cuts. Keep the cactus out of high-moisture areas to help ward off the growth of bacteria or fungi, which are leading factors in the death of cacti. An area from which the damage has been correctly removed will begin growing a new outer skin.