Saving a Cactus After Frost and Stem Collapse

A foot-tall prickly cactus was repotted, placed outdoors, possibly hit by a cat, then brought in for frost. It fell over, was buried deeper, and the next day the top broke off, revealing a hollow stem—dry rot from the base, possibly triggered by frost.

If tissue above the break is healthy (white, green, firm), cut there, let callous, and re-root the top. Discard the base, soil, and sterilize the pot—fungus/bacteria contaminate everything. Do not compost. This is a standard re-rooting procedure detailed in other answers.

Act fast: rot spreads quickly once the vascular tissue is compromised.