Why did this cactus rot?

A month ago I wrote a post about one of my favorite succulent container combinations: Silver Torch cacti (Cleistocactus straussii) and Agave schidigera 'Shira ito no Ohi'. In addition to the Silver Torch cacti planted in that pot, I had two others in a separate terracotta pot. They had grown just as much and I had plans to transfer them to a larger container this spring.


Like all my cacti, they were protected from the winter rains (not like it’s been a wet winter anyway). Much to my surprise, I noticed yesterday that the tallest of these two Silver Torch cacti had flopped over due to rot toward the bottom of the stem, an inch or so above soil level.


The soil is bone dry and I have no explanation what might have happened here. Sure, it’s possible that a stray rain drop or two might have landed on it during a rain storm, but if it’s that sensitive to moisture, wouldn’t it have rotted at the soil level?


On Friday afternoon I decided to do a radical amputation to save the patient’s life. Out came a sharp fillet knife, and in a split second I had cut off the rotten parts. I then dunked the cut surface in 70% isopropyl alcohol to seal it…


…and I drizzled some alcohol on the cut off section still in the pot. I’m hoping it will heal so the pup originating from the rotten stem will survive.


I placed the cut segment in a dry and shady spot where I will let it callus over for a month before planting it in a new container.


With temperatures warming up, I have every hope that it will survive and eventually become as healthy as the ones in the other pot:

120106_Cleistocactus strausii   Agave Shira ito no Ohi_01
Silver Torch cacti (Cleistocactus straussii) and
Agave schidigera 'Shira ito no Ohi'


  1. No ones undefeated... Its always a bit frustrating when something goes wrong even after precautions have been made. Nice safe

    1. I wish I could say I learned something from this. But I still don't know what happened.

  2. How weird! I wonder if a weird bug poked a hole in it and then it started to rot. But then again it seems so uniform. The rot I mean. If it is outside then maybe it was just the moisture in the air that did it. It is a puzzle isn't it. I hope the new one grows. I bet under your care it will!

    1. Candy, anything is possible. No matter how careful we are, something always goes wrong. But I'm sure I'll get the stem to re-root. (By the way, this is the duo I was going to give to you!)

  3. Of course it was the one I was going to get! LOL And I know I wish there was something to learn from this! It's just weird!

  4. Gerhard,
    I just noticed my beautiful cleistocactus straussii is leaning and I think there is the start of rot similar to yours: should I wait and see, or lop it off and try to re-root it like you did yours? I live in Pleasanton and have only had this cactus for 6 weeks or so. It could be in shock from the transfer from the nursery, I suppose. Penny

    1. Penny, I would take action now while it's still warm. Make a clean cut with a disinfected knife and let the cut surface callus over. Then put in very dry soil. Keep warm even if it means putting the cactus inside for the winter. Hope this helps.


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