Question
Hello!
We have three column shaped cactus that are about 3 feet tall in one container.  One of the cactus is starting to turn a black/brown in patches round the top.  Today I noticed that this particular cactus is also becoming very pale looking as well... and the patches are spreading.  We haven't watered it lately - and didn't think with this disease that it would be a good time to try.  The cactus is in our living room and wouldn't get a ton of light.  We normally water once a month, or less.
Is there anything we can do???

Answer
Dear Ann Marie,

I have answered a number of similar questions this month. Typically it is because the plant was exposed to extreme cold. Generally there are two reasons why a plant dies from the top down. Either the roots died a while ago (for whatever reason) or the plant was frozen as I mentioned. I can't tell without pictures what the base of the plant looks like, but if you know it was frost that did the damage, the plant may heal and branch from the base near the soil. Only then trim off the dead parts.

If you can send pictures, please send them to [email protected]. If the plant was not exposed to freezing temperatures, then I am afraid there's not much you can do. As far as watering goes, only water when the soil is dry, if it is too dry for too long, the roots will die back. In some plants this is not an issue.  Hopefully the remaining plants survive.

Sincerely,

Greg