Every fall, i bring my plants into my house including a large selection of cactii. I house them in my basement in an east facing room that gets decent indirect light but stays rather humid. Lately, my more mature and taller cactii have started to collapse. They dont rot at the bottom and they dont rot at the top. they rot from the middle. My latest victim, i sliced the top off, and there was another nub developing at the bottom.... I certainly dont water them all winter and they are several years old so they have survived the basement for several winters. It started a couple years ago with a madagascar palm. I had grown it to about 4 feet tall... it was beautiful.... it had survived one winter in my basement, but the second, it rotted near the base. i had two columnar cactii. the first was scraggly and ugly, but had budded off two more columns which were growing beautifully. suddenly, the original spire rotted and within days the whole thing was lost. the most recent column mentioned was about 7 years old and about 4 feet tall. it just started the budd at its base last summer. im really sad. they are like deaths in my family. I have a dehumidifier in the space now and am bringing everything out for the summer.... just looking for suggestions. I'm not quite sure to do with the cactus i just butchered. I can take pics of my space.... im just really bummed. LOL