What to do about a rotting, 27-year old cactus

Discussion in 'Cacti and Succulents' started by MTThornhill, Feb 5, 2016.

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  1. MTThornhill

    MTThornhill Member

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    Hi,

    I have had the cactus pictured for 27 years. Last week, I noticed that the bottom had gone black. I would assume rotting, but it had not been watered in 3 weeks, and it was in a "cactus potting mix" in a clay pot which I thought provided adequate drainage.

    I re-potted with new mix, but as I hope you can see in the photos, it is keeled over, and the blackness is spreading.

    I have read about cutting off rotten parts and starting over. Is that what I should be doing? Any good places to find how-to guidance?

    Thank you very much,
    Mordechai
     

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  2. mandarin

    mandarin Active Member 10 Years

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    Yes, that looks like rot. You still water it? My cacti are dormant now and have not been watered since September. So-called "cactus potting mixes" are rarely suitable for cacti, they hold too much water. Manufacturers seem to believe that a good cactus soil is just ordinary potting soil but with less fertiliser.

    You need to cut away all the infected tissue, that is until there are no dark spots left on the cut surface. Rot spreads much faster on the inside, and judging from experience I guess you will have to cut off about 2/3 of the stem do get a healthy cutting. Then it needs to form new roots before it dies from dehydration, and I don't know if your plant is big enough to do that.

    The method depends on what type of cactus it is and your local climate. There are many descriptions, including many variants, on the Internet, some good and some bad. Here is a one worth reading (the title is wrong, it is not about grafting):
    Grafting Cacti Areoles - How to graft cactus Areoles
    I generally leave cuttings of cacti similar to yours in a cool place to callous over for at least two months. When (if) some small roots start to protrude I put it in a pot with a slightly damp, coarse medium, like crushed brick. They are easily attacked by mold, so I don't bury the cuttings, I just let them rest on the surface and support them with sticks or the egde of the pot.
     
  3. MTThornhill

    MTThornhill Member

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    Thank you very much. I read your link and looked around on-line, and cut it. Attached are two pictures. I know nothing about this, and so I am concerned about the darkness of the hole in the middle. Any thoughts from those who know (far) more than I do?

    (And yes, I was still watering - lightly, on a monthly basis. I need to learn more about taking care of a cactus.)
     

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  4. mandarin

    mandarin Active Member 10 Years

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    The vascular bundle (in the center of the stem) is gone, rotted away (and that is where new roots usually emerge from). All the discoloured tissue must be removed, and I think there will be too little left for your plant to survive. If this was my plant and it was valuable to me I would first scoop out all remaining brown tissue. Depending on how much plant I have left I would:
    • See if it is willing to grow roots from some of the areoles, many cacti do that.
    • Wake up one of my (dormant) plants that I use as grafting stock, cut off as much as needed to get clean vascular tissue, and make a graft.
    • Discard it.
     
    Last edited: Feb 6, 2016
  5. MTThornhill

    MTThornhill Member

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    Thank you, Mandarin; I appreciate your help and timely replies. I'm going to try carving away the discoloured tissue...
     

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