Question
Dear Greg,
A couple of months ago, I purchased a cactus from Wal-mart and I do not know which kind of cactus it is. It has a green stem which has three sides and on the the top there is a red/orange bulb that is spherical in shape and also has little spikes along the sides. There are 8 lines of these spikes going along the sides of the bulb and are evenly spaced out and on one of those lines, there is another smaller bulb that seems to have grown out of it. I just want to know what kind of cactus it is, so that I may take better care of it.
Also I have another question, will exposing this cactus to radiation damage the plant in any way? I sit this cactus in front of my computer because supposedly it sucks all the "bad" stuff away from my computer.
Thanks a bundle Greg Simpson!
sincerely,
michael

Answer
Michael,

You have a "moon cactus", which is normally a Gymnocalycium mihanovichii grafted onto a Hylocereus. In my experience they don't live very long. However, here is a web page that may help: http://www.cactuscollection.com/info/cacti/grafted.html

Hope this helps.

Sincerely,

Greg