Asked September 10, 2019, 8:53 PM EDT
Anoka County Minnesota
Thanks for the question.
I enjoyed the picture you sent as your cactus looks virtually identical to one that I have grown for over 15 years. I believe that it is some type of Euphorbiaceae although this group is extremely diverse. I see that you have some browning at the base of your plant. The same is true for the one I have. This browning (“corking”) is common at the base as a cactus ages. Presumably it has no effect upon the overall health of the cactus.
I have asked other Master Gardeners about splitting and the only information that I received was that it depends upon what the root system looks like. You only way that you will know something about the root system of your cactus is to remove it from its container. This will be no small feat for an eight-foot cactus! If each of the three stems has their own root system (which I doubt), then you should be able to divide things. If so, use a very sharp knife that you sterilize with a 10% bleach solution (1 part of commercial bleach to 9 parts of water). I would attempt to do this after the soil around the cactus has completely dried. If it appears that all stems join together at the base (crown) into a single root (more likely), then splitting would not be possible.
I completely understand your desire to share this plant with others. Perhaps you could experiment with making cuttings? This would certainly be less disruptive to the plant than dislodging it from the pot. It might be worth a try. Here is some information about doing this:
Good luck with your project!!