Unknown columnar cactus rotted from the top

[silverman166]

This is a general question relating to the best way to treat a columnar cactus which has rotted from the top part-way down the stem.
Mine has five basal stems, the largest being ~6" tall x1.5" across. Three of the stems have rotted from the top, including the tallest. I have cut the damaged portions off, which were very mushy inside, back to what looks good ie solid, whitish,cut-cucumber-like (!).

What I want to know is what is the likelihood of any growth appearing from the cut stems, or would it be better to cut my losses and remove them entirely, leaving the two, hopefully unaffected, stems? If growth is possible, should the cuts be angled slightly, and dusted with flowers of sulphur or somesuch? I have brought the plant indoors now.

I'm also curious as to the possible cause. The plant was a Christmas present last year and was kept indoors until October, when I put it in the greenhouse with the rest of my collection. The minimum temperature was 5C. Whilst I appreciate that the cactus is not identified, how likely is it that the temperature change could have caused this problem?

I have been wary of overwatering, in fact if anything I've underwatered, although the plant looked healthy enough before going into the greenhouse.

Thanks for you interest.

[7george]

Excessive wetness in your greenhouse? Are there some black or rust spots over the cactus?
A picture would help for suggestions.

[esp_imaging]

Where in the world do you live? It really helps to know. Photos would help too.

If the stems were close to the glass they may have been colder than your general greenhouse temp.
No need to angle cuts. Most columnar cactus plants will send out new branches from below the cut. If it has a strong basal branching character, maybe it will just sprout from ground level.

[silverman166]

Thanks for your replies, 7george and esp_imaging. For the record, I'm in Yorkshire, England - I've updated my profile to show that.

There are no signs of fungus or other diseases, and unfortunately I didn't take photos before I did the surgery - the post was almost an afterthought!

I don't feel excessive damp is the problem, as there's no condensation anywhere within the bubble wrap 'tent' I've made , and what heat is applied is done by electric fan heater, giving a little air movement, and avoiding the damp from some other forms of heating. Other plants and cacti in there seem to be reasonably healthy.
The plant was not near the glass, which is insulated somewhat by bubble wrap, and the minimum temperature was from a thermometer located on the bench nearby. Presumably this cactus needs a higher minimum temperature?

It's good to know that there's a strong likelihood of further branching occurring in the future.

Thanks for your interest and informative replies.