This morning the thermometer indicated -5° C (23° F). That was under the eaves, so it was probably even colder in the garden. So, we have now involuntarily answered the question, “what happens when you freeze a five foot tall cactus?”.
First, it droops.
The next day, if there’s more frost, it cracks, splits, explodes into pieces.
The core of the plant stands for a time, surrounded by branches lying on the ground, until further frosts cause it too to shatter. We imagine that nothing will remain but a stump.
With warm weather in spring, perhaps it will re-sprout. Perhaps we’ll replace this variety of cactus with something more frost tolerant, maybe a variety with some kind of natural anti-freeze sap. We could also root a branch, assuming that it didn’t freeze solid into a dead, useless cactus-sickle.
It’s unlikely that this cactus will remain standing for long. The joints have cracks, the deep freeze is likely to continue, and the branches are still falling to the ground.
We’ve noticed other varieties of prickly pear (Opuntia) in the area have fared better than our plant. They tend to be either pricklier or greener. There are other varieties of cactus that tolerate low temperatures in case we decide to keep a cactus in this plant’s location.